thermoelectric conversion module

Abstract

This thermoelectric conversion module is formed by electrically connecting, by a conductive member, one end of an n-type thermoelectric conversion element having a negative Seebeck coefficient and having a half-Heusler structure to one end of a p-type thermoelectric conversion element containing an oxide having a positive Seebeck coefficient at a temperature of 25°C or higher. The conductive member is connected to the n-type thermoelectric conversion element and the p-type thermoelectric conversion element through a connection layer containing a conductive metal comprising silver, and the connection layer is characterized by further containing an oxide to reduce the bond resistance between the n-type thermoelectric conversion element and / or the p-type thermoelectric conversion element.

Description

[Technical Field]

[0001] The present invention relates to a thermoelectric conversion module, and more particularly to a thermoelectric conversion module that operates over a wide temperature range from room temperature to approximately 500°C. [Background technology]

[0002] In Japan, the rate of useful energy obtained from primary energy supplies is around 30%, with approximately 70% of the energy being discarded into the atmosphere as heat. In addition, heat generated by combustion in factories, waste incinerators, etc. is discarded into the atmosphere without being converted into other energy sources. In this way, we humans waste a huge amount of thermal energy and obtain only a small amount of energy from activities such as burning fossil fuels.

[0003] To improve energy efficiency, it is effective to utilize the thermal energy that is discarded in the atmosphere. To achieve this, thermoelectric conversion, which converts thermal energy directly into electrical energy, is considered to be an effective means. Thermoelectric conversion utilizes the Seebeck effect, and is an energy conversion method that generates electricity by generating a potential difference by creating a temperature difference between both ends of a thermoelectric conversion material.

[0004] In this type of power generation using thermoelectric conversion, i.e., thermoelectric power generation, electricity is generated simply by placing one end of a thermoelectric conversion material in a high-temperature area generated by exhaust heat and the other end in the atmosphere or a water-cooled low-temperature area, and connecting an external resistor to both ends. This eliminates the need for moving devices such as motors or turbines required for general power generation. This makes it inexpensive, allows for long-term use, does not emit gases due to combustion, and can generate electricity continuously until the thermoelectric conversion module deteriorates. Furthermore, because thermoelectric power generation is capable of generating electricity at a high power density, the generator (module) itself can be made small and lightweight, making it possible to use it as a portable power source for devices such as mobile phones and laptops.

[0005] As such, thermoelectric power generation is expected to play a part in solving the energy problems that are looming in the future. However, to realize thermoelectric power generation, a thermoelectric conversion module with high conversion efficiency and made of thermoelectric conversion materials with excellent heat resistance and chemical durability is required. A thermoelectric conversion module is a power generator in which one or more p-type and n-type thermoelectric conversion materials are alternately connected in series. However, the development of thermoelectric conversion modules has currently lagged behind the development of thermoelectric conversion materials themselves, due to the difficulty of achieving good electrical, chemical, and mechanical bonding between the thermoelectric elements (p-type or n-type thermoelectric conversion elements) and electrodes.

[0006] CoO2-based layered oxides such as Ca3Co4O9 and Bi2Sr2Co2O9 have been reported to exhibit excellent thermoelectric performance in high-temperature air (see Non-Patent Documents 1 and 2). These materials are p-type thermoelectric conversion materials.

[0007] To improve the efficiency of thermoelectric conversion modules, not only p-type but also high-performance n-type thermoelectric conversion materials are required. Until now, thermoelectric conversion modules have been manufactured using CaMnO3 and LaNiO3, n-type thermoelectric conversion materials that are durable even at high temperatures (see Non-Patent Documents 3 and 4). In thermoelectric conversion modules that use oxides such as CaMnO3 and LaNiO3 as n-type thermoelectric conversion elements, the thermoelectric conversion elements and conductive members are joined using a conductive paste containing silver, gold, or platinum as conductive materials. However, the power generation performance of these n-type thermoelectric conversion materials is lower than that of p-type materials, resulting in low power generation efficiency of the modules.

[0008] Silicides such as Mn3Si4Al2 (see Patent Document 1) and half-Heusler alloys such as TiNiSn and ZrNiSn (see Non-Patent Document 5) have been reported as n-type thermoelectric conversion materials that exhibit good thermoelectric conversion performance in air from room temperature to high temperatures of about 600°C and also have excellent oxidation resistance.

[0009] Among the thermoelectric conversion materials mentioned above, half-Heusler alloy thermoelectric conversion materials made of TiNiSn or ZrNiSn exhibit good thermoelectric conversion performance and oxidation resistance even in air in the temperature range from room temperature to approximately 500°C.

[0010] In a thermoelectric module using these thermoelectric materials as n-type thermoelectric materials, the n-type thermoelectric elements and conductive members are joined by copper brazing in a vacuum. The output of this thermoelectric module measured in a vacuum was 2 W / cm. 2 is. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-124243 [Patent Document 2] International Publication No. 2005 / 036661 [Patent Document 3] International Publication No. 2015 / 174462 [Non-patent literature]

[0012] [Non-Patent Document 1] R. Funahashi et.al., Jpn. J. Appl. Phys. 39, L1127 (2000). [Non-patent document 2] R.Funahashi et.al.,Appl.Phys.Lett.,Vol.76,No.17,pp.2385(2000). [Non-patent document 3] R. Funahashi et.al.,Appl.Phys.Lett.,Vol.85,No.6,pp.1036(2004). [Non-patent document 4] S. Urata et.al.,Intl.J.Appl.Ceram.Tech.,Vol.4,No.6,pp.535(2007). [Non-patent document 5] S.Sakurada et.al.,Appl.Phys.Lett.,Vol.86,No.8,082105(2005). [Non-patent document 6] K. Bartholome et.al., J. Elec. Mater., Vol. 43, No. 6, pp. 1775 (2014). Summary of the Invention [Problem to be solved by the invention]

[0013] However, in conventional thermoelectric conversion modules, the thermoelectric conversion element and conductive member are joined using metal materials that melt, such as solder and brazing, as connection layers. Solder generally contains alloy materials that melt at temperatures below 450°C, so it cannot be used when using thermoelectric modules at 500°C because it will melt. Brazing also generally uses alloys known as "filler metals," which have a higher melting temperature than solder. The melting point of the filler metal must be lower than that of the materials being joined.

[0014] Oxide materials, half-Heusler alloys, and silicide materials are known to be thermoelectric conversion materials that are durable at temperatures up to 500°C. The electrode materials connecting p-type and n-type thermoelectric conversion elements made of such materials must also be resistant to oxidation and other degradation at high temperatures. While precious metals such as gold and platinum, or silver, are suitable for this purpose, silver is preferred for economic reasons. Consequently, when forming joints using silver solder, alloys with lower melting points than silver must be used. These alloys typically contain metals such as zinc, copper, and cadmium. Adding these metals increases the risk of oxidation at 500°C, making it difficult to generate thermoelectric power stably over long periods of time. Therefore, thermoelectric conversion modules must be used in a vacuum or inert gas atmosphere.

[0015] Furthermore, to achieve low joint resistance between the thermoelectric conversion material and the electrodes and high joint strength against thermal stress when a temperature difference occurs, it is effective to use a joint material with a composition that is appropriate for the components of the thermoelectric conversion material and the electrodes. Because brazing materials are alloys, only metals can be added to optimize the composition. Furthermore, it is difficult to create a uniform alloy within a desired solid solution range by adding additives, making it difficult to optimize the joint material. Furthermore, because brazing requires the use of a burner to form each joint, it is not suitable for mass production of thermoelectric conversion modules with multiple joints.

[0016] The present invention has been made in consideration of the above circumstances, and aims to provide a thermoelectric conversion module that uses a bonding material that can exhibit good thermoelectric conversion performance in a temperature range from about 50°C to about 500°C, and that can maintain excellent performance for a long period of time with almost no reduction in output. [Means for solving the problem]

[0017] The present invention provides a thermoelectric conversion module comprising an n-type thermoelectric conversion element having a half-Heusler structure with a negative Seebeck coefficient and a p-type thermoelectric conversion element containing an oxide with a positive Seebeck coefficient at a temperature of 25°C or higher, the ends of which are electrically connected to each other by a conductive member, wherein the conductive member is connected to the n-type thermoelectric conversion element and the p-type thermoelectric conversion element via a connection layer containing a conductive metal made of silver, and the connection layer further contains an oxide so as to reduce the junction resistance with the n-type thermoelectric conversion element and / or the p-type thermoelectric conversion element.

[0018] According to an embodiment of the present invention, (Configuration 1) a thermoelectric conversion module includes: x B yThe thermoelectric conversion element has a half-Heusler structure and a negative Seebeck coefficient, and is represented by NiSn (A is Ti or Zr, B is at least one of Hf and Zr when A is Ti, and at least one of Hf and Ti when A is Zr, and 0.5≦x≦1, 0≦y≦0.5). One end of the thermoelectric conversion element is connected to one end of the n-type thermoelectric conversion element, and Ca 3-j Bi j Co4O9(0≦j≦0.5) or Bi 2.0+k M 2.0+m The device comprises a p-type thermoelectric conversion element containing an oxide having a positive Seebeck coefficient at temperatures of 25°C or higher and represented by Co2O9 (where M is at least one of Ca and Sr, and -0.2≦k≦0.2, -0.2≦m≦0.2), and a conductive member connected to one end of an n-type thermoelectric conversion element and one end of the p-type thermoelectric conversion element by silver paste, and the resistivity of the silver paste measured by a four-probe method is 2.60 μΩcm to 13.0 μΩcm.

[0019] (Configuration 2) In configuration 1, the silver paste contains an additive made of at least one of silver oxide and titanium oxide, or an oxide used in p-type thermoelectric conversion elements.

[0020] (Configuration 3) In Configuration 1 or 2, the silver paste includes a first silver paste and a second silver paste. The first silver paste is disposed between one end of the n-type thermoelectric conversion element and the conductive member. The second silver paste is disposed between one end of the p-type thermoelectric conversion element and the conductive member. The first silver paste includes an additive made of at least one of titanium oxide and silver oxide. The second silver paste includes an additive made of at least one of titanium oxide and silver oxide, or an oxide used in the p-type thermoelectric conversion element.

[0021] (Configuration 4) In configuration 3, the second silver paste contains an additive different from that of the first silver paste. Also, (Configuration 5) In configuration 3, the second silver paste contains the same additive as that of the first silver paste.

[0022] (Configuration 6) In any one of configurations 3 to 5, the conductive member is made of any one of gold, silver, and platinum.

[0023] (Configuration 7) In any of configurations 1 to 6, the area of ​​the surface of the p-type thermoelectric conversion element parallel to the contact surface with the conductive member is larger than the area of ​​the surface of the n-type thermoelectric conversion element parallel to the contact surface with the conductive member.

[0024] According to the above, there is almost no decrease in output, and excellent performance can be maintained for a long period of time. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic diagram of a thermoelectric conversion module according to an embodiment of the present invention. [Figure 2] 2 is a top view of the thermoelectric conversion module as seen from a direction A shown in FIG. 1. FIG. [Figure 3] 2 is a side view of the thermoelectric conversion module as seen from direction B shown in FIG. 1. FIG. [Figure 4] 2 is a bottom view of the thermoelectric conversion module as seen from direction C shown in FIG. 1. FIG. [Figure 5] FIG. 2 is a process diagram showing a method for manufacturing an n-type thermoelectric conversion element. [Figure 6] FIG. 10 is an exploded perspective view of another thermoelectric conversion module according to an embodiment of the present invention. [Figure 7] FIG. 10 is an exploded perspective view of still another thermoelectric conversion module according to an embodiment of the present invention. [Figure 8] FIG. 2 is a graph showing the temperature dependence of the dimensionless figure of merit ZT in Example 1 and Comparative Example 1. [Figure 9] FIG. 1 is a diagram showing the relationship between the Seebeck coefficient and the thermal conductivity in the n-type thermoelectric conversion elements of Examples 1, 3 to 6, 7 to 10, 19 to 27, 28 to 31, and 32 to 37. [Figure 10] FIG. 2 is a diagram showing the relationship between voltage, power generation output, and current in a thermoelectric conversion module. [Figure 11]FIG. 10 is a graph showing the relationship between maximum output and heating temperature in Examples 38 and 39 and Comparative Example 2. [Figure 12] FIG. 10 is a diagram showing the relationship between the maximum output and the heating temperature in the thermoelectric conversion module of Example 294. [Figure 13] FIG. 10 is a diagram showing the relationship between power generation output and power generation time in the thermoelectric conversion modules of Examples 294 and 295. [Figure 14] FIG. 10 is a graph showing the relationship between the maximum output and the content of Ag 2 O added to the p-type silver paste and the n-type silver paste in the thermoelectric conversion modules of Examples 38 to 41, 47, and 48. [Figure 15] FIG. 10 is a graph showing the relationship between the maximum output and the content of TiO 2 added to the p-type silver paste and the n-type silver paste in the thermoelectric conversion modules of Examples 38, 49 to 51, 57, and 58. [Figure 16] FIG. 10 is a graph showing the relationship between the maximum output and the content of TiO2 added to the p-type silver paste in the thermoelectric conversion modules of Examples 38, 62, 63, and 69. [Figure 17] FIG. 10 is a graph showing the relationship between the maximum output and the content of Ca2.7Bi0.3Co4O9 added to the p-type silver paste in the thermoelectric conversion modules of Examples 38 and 72 to 75 and the thermoelectric conversion modules of Examples 38 and 86 to 89. [Figure 18] FIG. 10 is a graph showing the relationship between the maximum output and the content of Ag 2 O added to the n-type silver paste in the thermoelectric conversion modules of Examples 38 and 81 to 85. [Figure 19] FIG. 10 is a graph showing the relationship between the maximum output and the content of TiO 2 added to the n-type silver paste in the thermoelectric conversion modules of Examples 38, 90, 95 to 98 and Examples 271, 288 to 291. [Figure 20] FIG. 10 is a graph showing the relationship between the maximum output of the thermoelectric conversion modules of Examples 248 and 265 to 268 and the content of TiO 2 added to the n-type silver paste. DETAILED DESCRIPTION OF THE INVENTION

[0026] Fig. 1 is a schematic diagram of a thermoelectric conversion module according to an embodiment of the present invention. Fig. 2 is a top view of the thermoelectric conversion module as seen from direction A shown in Fig. 1. Fig. 3 is a side view of the thermoelectric conversion module as seen from direction B shown in Fig. 1. Fig. 4 is a bottom view of the thermoelectric conversion module as seen from direction C shown in Fig. 1.

[0027] 1 to 4, a thermoelectric conversion module 10 according to an embodiment of the present invention includes insulating substrates 1 and 12, conductive members 2, 3, and 11, connection layers (conductive pastes) 4, 5, 8, and 9, n-type thermoelectric conversion elements 6, and p-type thermoelectric conversion elements 7. Note that the insulating substrates 1 and 12 are electrically insulated (the same applies hereinafter).

[0028] The conductive members 2 and 3 are arranged on the insulating substrate 1 in contact with the insulating substrate 1. In this case, the conductive members 2 and 3 are arranged at a predetermined distance from each other. The connection layer (conductive paste) 4 is arranged in contact with the conductive member 2 and the n-type thermoelectric conversion element 6 and is disposed between the conductive member 2 and the n-type thermoelectric conversion element 6. The connection layer (conductive paste) 5 is arranged in contact with the conductive member 3 and the p-type thermoelectric conversion element 7 and is disposed between the conductive member 3 and the p-type thermoelectric conversion element 7.

[0029] The n-type thermoelectric conversion element 6 is in contact with the connection layers (conductive paste) 4 and 8 and is disposed between the connection layer (conductive paste) 4 and the connection layer (conductive paste) 8. The p-type thermoelectric conversion element 7 is in contact with the connection layers (conductive paste) 5 and 9 and is disposed between the connection layer (conductive paste) 5 and the connection layer (conductive paste) 9. The connection layer (conductive paste) 8 is in contact with the n-type thermoelectric conversion element 6 and the conductive member 11 and is disposed between the n-type thermoelectric conversion element 6 and the conductive member 11.

[0030] The connection layer (conductive paste) 9 is in contact with the p-type thermoelectric conversion element 7 and the conductive member 11 and is disposed between the p-type thermoelectric conversion element 7 and the conductive member 11. The conductive member 11 is in contact with the connection layers (conductive paste) 8, 9 and the insulating substrate 12 and is disposed between the connection layers (conductive paste) 8, 9 and the insulating substrate 12.

[0031] As a result of the conductive members 2, 3, and 11, the connection layers (conductive pastes) 4, 5, 8, and 9, the n-type thermoelectric conversion element 6, and the p-type thermoelectric conversion element 7 being arranged as described above, one ends of the n-type thermoelectric conversion element 6 and the p-type thermoelectric conversion element 7 are electrically connected to each other via the connection layers (conductive pastes) 8 and 9 and the conductive member 11, the other end of the n-type thermoelectric conversion element 6 is electrically connected to the conductive member 2 via the connection layer (conductive paste) 4, and the other end of the p-type thermoelectric conversion element 7 is electrically connected to the conductive member 3 via the connection layer (conductive paste) 5. In other words, the n-type thermoelectric conversion element 6 and the p-type thermoelectric conversion element 7 are electrically connected in series between the conductive member 2 and the conductive member 3.

[0032] Each of insulating substrates 1 and 12 is made of oxide ceramics, nitride ceramics, or carbide ceramics, such as aluminum oxide, zirconium oxide, titanium oxide, magnesium oxide, silicon oxide, silicon nitride, aluminum nitride, titanium nitride, and silicon carbide.

[0033] Furthermore, each of the insulating substrates 1, 12 is not limited to the above materials, and generally may be made of an insulating material with high thermal conductivity that does not melt or break at temperatures higher than the usable range of the thermoelectric conversion module 10 (for example, about 800°C when the upper limit of the usable range of the thermoelectric conversion module 10 is 500°C), is chemically stable, and does not react with the thermoelectric conversion elements and conductive members.

[0034] By using substrates with high thermal conductivity as the insulating substrates 1, 12, the temperature of the high-temperature parts of the n-type thermoelectric conversion element 6 and the p-type thermoelectric conversion element 7 can be brought closer to the temperature of the high-temperature heat source, and the temperature difference can be increased, thereby improving the power generation output of the thermoelectric conversion module 10.

[0035] The shape of the insulating substrates 1, 12 is not particularly limited and may be determined according to the shape and size of the high-temperature and low-temperature parts of the thermoelectric conversion module 10. However, taking into consideration heat transfer in the high-temperature parts and heat dissipation in the low-temperature parts of the thermoelectric conversion module 10, it is preferable that the thickness of the insulating substrates 1, 12 be as thin as possible, and for example, a thickness of approximately 0.1 to 5 mm is most preferable.

[0036] Furthermore, in the thermoelectric conversion module 10, instead of covering the n-type thermoelectric conversion elements 6 and the p-type thermoelectric conversion elements 7 with a single insulating substrate having an area larger than the area of ​​the arrangement region of the n-type thermoelectric conversion elements 6 and the p-type thermoelectric conversion elements 7, the n-type thermoelectric conversion elements 6 and the p-type thermoelectric conversion elements 7 may be covered with an insulating substrate 12 having the same dimensions as the conductive member 11.

[0037] Each of the connection layers (conductive paste) 4, 5, 8, and 9 is made of a conductive paste containing silver, a conductive paste containing silver and silver oxide, a conductive paste containing silver and titanium oxide, or a conductive paste containing silver, silver oxide, and titanium oxide.

[0038] Here, we explain the reasons for adding silver oxide or titanium oxide to the silver-containing conductive paste. First, when the silver-containing conductive paste is solidified to form a junction between a thermoelectric conversion element and silver, the electron energy states differ (the Fermi levels differ), resulting in the formation of a Schottky barrier. This increases the electrical resistance (junction resistance) at the junction interface, causing an increase in the internal resistance of the thermoelectric conversion module. Therefore, in order to reduce this difference in Fermi levels, we aim to reduce the junction resistance by moving the Fermi level of the conductive paste placed between the electrode and the thermoelectric conversion element closer to the thermoelectric conversion element. The surface of the half-Heusler alloy used in the thermoelectric conversion element is also covered with an oxide film. We have found that, in this case, the junction resistance can also be reduced by adding a specific metal oxide to the conductive paste. This is demonstrated in the examples described below.

[0039] In addition, when a conductive paste containing silver forms a bond with a thermoelectric conversion element, the conductive paste penetrates into the unevenness of the surface of the thermoelectric conversion element, providing a mechanical bond due to the anchor effect after solidification. At the same time, a chemical bond is also formed between the metal atoms in the thermoelectric conversion element and the silver atoms in the conductive paste via oxygen. To achieve this, we searched for oxide species and their composite amounts that form strong bonds between the metal elements in the thermoelectric conversion element and the silver in the conductive paste from transition metal oxides that can desorb oxygen by heating, etc. This is also shown in the examples below.

[0040] The connection layers (conductive paste) 4, 8 are made of a conductive paste for connecting the n-type thermoelectric conversion element 6 to the conductive members 2, 11, and the connection layers (conductive paste) 5, 9 are made of a conductive paste for connecting the p-type thermoelectric conversion element 7 to the conductive members 3, 11. Therefore, the connection layers (conductive paste) 4, 8 may be made of a conductive paste different from the connection layers (conductive paste) 5, 9. The connection layers (conductive paste) 5, 9 may be made of a conductive paste containing silver and an oxide powder having the same crystal structure as the p-type thermoelectric conversion element 7.

[0041] The conductive metal blended into the conductive paste is silver only, and is typically blended in powder form. The diameter of the silver powder is not particularly limited, but is typically 100 μm or less, preferably 50 μm or less, and more preferably 10 μm or less. Silver powder is generally sintered by heating at approximately 300°C to 600°C, resulting in a decrease in electrical resistance. When using a silver paste containing such silver powder in a thermoelectric conversion module, it is preferable to obtain low electrical resistance by sintering the silver powder. However, sintering the silver powder is not necessarily required as long as the required electrical resistance can be reduced without sintering the silver powder. The silver in the silver paste used in the following examples is sintered at 300°C or higher. However, the sintering start temperature of silver may vary depending on the additives and the amounts of the additives used in the embodiments of the present invention.

[0042] The silver oxide mixed into the conductive paste is disilver monoxide (Ag2O), and the titanium oxide mixed into the conductive paste is any one of titanium dioxide (TiO2), titanium trioxide (Ti2O3), and titanium monoxide (TiO).

[0043] Titanium oxide turns into titanium dioxide when heated in air, so it is preferable to use titanium dioxide at the stage of preparing the conductive paste.

[0044] The amount of titanium oxide, when used alone, is 0.1 to 10% by weight, more preferably 0.1 to 6% by weight, based on 100% by weight of the conductive paste when wet. The amount of silver oxide, when used alone, is 0.2 to 10% by weight, more preferably 0.2 to 8% by weight, based on 100% by weight of the conductive paste when wet. Furthermore, when both silver oxide and titanium oxide are added, the amounts of silver oxide and titanium oxide are each 0.5 to 5% by weight, more preferably 0.5 to 2% by weight.

[0045] The silver oxide is usually blended in the conductive paste in powder form. The particle size of the silver oxide is not particularly limited, but is 100 μm or less, preferably 50 μm or less, and more preferably 15 μm or less. The particle size of the titanium oxide is also not particularly limited, but is 100 μm or less, preferably 50 μm or less, and more preferably 15 μm or less.

[0046] The oxide powder to be mixed in the conductive paste used for connecting the p-type thermoelectric conversion elements 7 is not particularly limited as long as it has the same crystal structure as the p-type thermoelectric conversion elements 7. 3-j Bi j Co4O9(0≦j≦0.5), or Bi 2.0+k M 2.0+m It is sufficient that the material is Co2O9 (M is at least one of Ca and Sr, and -0.2≦k≦0.2, -0.2≦m≦0.2), and preferably has the same composition as the p-type thermoelectric conversion element 7.

[0047] Furthermore, the particle size of the oxide powder mixed into the conductive paste used to connect the p-type thermoelectric conversion elements 7 is not particularly limited, but is 100 μm or less, preferably 50 μm or less, and more preferably 30 μm or less.

[0048] The amount of oxide powder mixed into the conductive paste used to connect the p-type thermoelectric conversion element 7 is 0.1 to 10 wt %, preferably 1 to 8 wt %, and more preferably 3 to 6 wt %, relative to 100 wt % of the conductive paste when wet.

[0049] The connection layers (conductive pastes) 4, 5, 8, and 9 may contain, in addition to the above-mentioned silver, silver oxide, titanium oxide, and oxides having the same crystal structure as the p-type thermoelectric conversion element 7, glass powder (frit) components, resin components, solvent components, etc.

[0050] Glass powder is a component that primarily exerts bonding strength when the conductive paste is applied to a connection portion and heated. Glass powder generally softens at temperatures of approximately 450°C to 700°C, and then solidifies to exert bonding strength. Such glass powder may be appropriately selected from glass components blended into known conductive pastes. For example, borosilicate bismuth glass and borosilicate lead glass can be used. Considering environmental and health aspects, it is preferable to use lead-free glass components. The softening temperature of the glass powder in the silver paste used in the following examples is approximately 500°C. However, the softening temperature of the glass may vary depending on the additives and the amounts of the additives added.

[0051] The resin component provides the conductive paste with appropriate dispersibility, thixotropy, viscosity characteristics, etc. Examples of the resin component that can be used include ethyl cellulose, hydroxyethyl cellulose, methyl cellulose, nitrocellulose, ethyl cellulose derivatives, acrylic resins, butyral resins, alkyd phenolic resins, epoxy resins, and wood rosin.

[0052] The solvent component may be any substance that can uniformly disperse all of the above-mentioned components, has a suitable viscosity to prevent dripping during and after application, and is liquid at room temperature that decomposes or dissipates when heated. For example, toluene, cyclohexane, isopropyl alcohol, diethylene glycol monobutyl ether acetate (butyl carbitol acetate), terpineol, etc. may be used as the solvent component.

[0053] The blending ratio of these components is not limited and may be appropriately determined depending on the desired electrical conductivity, thermal expansion coefficient, bonding strength, viscosity characteristics, etc. The content of the glass component can be, for example, about 0.5 to 50% by weight relative to 100% by weight of silver, but may be outside this range.

[0054] The content of the resin component is not particularly limited and may be determined as appropriate within a range that allows for suitable workability or adhesiveness. For example, it may be approximately 0.5 to 50% by weight relative to 100% by weight of silver, but may be outside this range. The content of the solvent component may be approximately 10 to 100% by weight relative to 100% by weight of silver, but may be outside this range.

[0055] Furthermore, the connection layers (conductive pastes) 4, 5, 8, and 9 may contain plasticizers, lubricants, antioxidants, viscosity adjusters, and the like that are compounded in known conductive pastes.

[0056] There are no particular limitations on the method for preparing the connection layers (conductive pastes) 4, 5, 8, and 9. For example, silver, silver oxide, titanium oxide, and at least one oxide having the same crystal structure as the p-type thermoelectric conversion element 7 may be mixed, and then other components may be added and kneaded; alternatively, a commercially available paste containing silver may be kneaded with silver oxide, titanium oxide, and at least one oxide having the same crystal structure as the p-type thermoelectric conversion element 7.

[0057] The connecting layers (conductive pastes) 4, 5, 8, and 9 can be used to connect either an n-type thermoelectric conversion element made of an alloy with a half-Heusler structure or a p-type thermoelectric conversion element made of an oxide to a conductive member, except when they contain an oxide having the same crystal structure as the p-type thermoelectric conversion element 7.

[0058] On the other hand, the connection layers (conductive pastes) 4, 5, 8, and 9 containing an oxide having the same crystal structure as the p-type thermoelectric conversion element 7 can be used when connecting a p-type thermoelectric conversion element made of an oxide to a conductive member.

[0059] By joining the thermoelectric conversion element to the conductive member using the connection layers (conductive pastes) 4, 5, 8, and 9, it is possible to impart appropriate conductivity to the joint of the thermoelectric conversion element and provide sufficient joint strength. Furthermore, even when power generation is repeated at high temperatures, peeling or the components contained in the connection layers (conductive pastes) 4, 5, 8, and 9 do not diffuse widely into the thermoelectric conversion material, and good thermoelectric conversion performance can be maintained for a long period of time.

[0060] The conductive members 2, 3, and 11 may be made of a material having an electrical resistance value sufficiently lower than that of the n-type thermoelectric conversion elements 6 and the p-type thermoelectric conversion elements 7. The conductive members 2, 3, and 11 are preferably in a sheet shape, as they preferably have high thermal conductivity and cover the connection surfaces of the n-type thermoelectric conversion elements 6 and the p-type thermoelectric conversion elements 7. The conductive members 2, 3, and 11 may be made of a metal thin film (or metal layer) formed on one surface of an insulating ceramic substrate or the like, a conductive ceramic substrate, or a metal plate (or metal substrate).

[0061] Of these, the metal for the conductive metal layer or conductive metal substrate must be one that does not oxidize or melt at the operating temperature of the thermoelectric conversion module 10. Considering stability at high temperatures, for example, a metallic material made of a precious metal or an alloy containing about 30% by weight or more, preferably about 70% by weight or more, of a precious metal can be used. Examples of precious metals include silver, gold, platinum, and palladium. In addition to the above-mentioned precious metals, base metals can also be used as the conductive metal placed on the low-temperature side during thermoelectric power generation. Examples of base metals include copper, iron, titanium, and aluminum.

[0062] The conductive ceramic is preferably a material that does not deteriorate in air at high temperatures of about 500°C and can maintain low electrical resistance for a long period of time. For example, an oxide sintered body with low electrical resistivity can be used as the conductive ceramic. Examples of such oxide sintered bodies include LaNiO3 and RuO3.

[0063] The oxide sintered body is produced as follows. The raw materials are mixed so that the elemental component ratio is similar to that of the target oxide, and the mixture is fired to produce the oxide sintered body. In general, the oxide sintered body can be produced by a solid-state reaction method. The firing temperature and firing time are not particularly limited as long as they are conditions under which the desired oxide is formed, but for example, they are in the temperature range of about 700 to 1000° C. for about 10 to 40 hours.

[0064] When carbonates and organic compounds are used as raw materials, it is preferable to calcinate the raw materials in advance to decompose them, and then calcinate them to form the target oxide. For example, when carbonates are used as raw materials, they may be calcined at about 700 to 900°C for about 10 hours, and then calcined under the above-mentioned conditions.

[0065] The calcination means is not particularly limited, and any means such as an electric heating furnace or a gas heating furnace can be used. The calcination atmosphere is usually an oxidizing atmosphere. Examples of the oxidizing atmosphere include an oxygen stream and air. When the raw material contains a sufficient amount of oxygen, calcination can be performed in, for example, an inert atmosphere.

[0066] To produce the desired oxide by the solid-state reaction method, it is preferable to press-form the raw material powder into a compact and then sinter it in order to efficiently proceed with the solid-state reaction. The resulting sintered compact is then cut, ground, and polished to form a conductive member to be used in the thermoelectric conversion module 10.

[0067] The dimensions of the conductive members 2, 3, and 11 can be determined based on the thermoelectric conversion elements (n-type thermoelectric conversion elements 6 and p-type thermoelectric conversion elements 7) and the amount of power generation, but it is preferable for them to widely cover the connection surfaces of the thermoelectric conversion elements (n-type thermoelectric conversion elements 6 and p-type thermoelectric conversion elements 7).

[0068] To make the surface of insulating ceramics conductive, a conductive material is combined with insulating ceramics that do not oxidize even in air at high temperatures of around 500°C. For example, a substrate made of oxide ceramics such as alumina and nitride ceramics such as aluminum nitride can be used as the insulating ceramic. The metal coating formed on the insulating ceramic is, for example, a precious metal or precious metal alloy coating. Examples of precious metals include silver, gold, and platinum. The precious metal or precious metal alloy coating can be formed by vapor deposition or by applying a conductive paste containing the precious metal (or alloy coating).

[0069] As the conductive members 2, 3, and 11, a material with low electrical resistance is preferred to increase the output from the thermoelectric conversion module 10, and furthermore, from the viewpoint of processability, a sheet metal that is flexible and not easily broken is preferred, and in particular, a silver sheet is preferred from the viewpoints of price, electrical resistivity, and thermal conductivity.

[0070] The length, width, and thickness of the conductive members 2, 3, and 11 may be appropriately set according to the size, electrical resistivity, thermal conductivity, and other factors of the thermoelectric conversion elements (n-type thermoelectric conversion element 6 and p-type thermoelectric conversion element 7). Furthermore, high thermal conductivity is necessary to efficiently transfer heat from the heat source to the high-temperature portions of the thermoelectric conversion elements (n-type thermoelectric conversion element 6 and p-type thermoelectric conversion element 7) and to efficiently dissipate heat from the low-temperature portions. Therefore, it is desirable to make the thickness as thin as possible. For example, it is particularly preferable to use a silver sheet having a thickness of approximately 0.01 to 3 mm as the conductive members 2, 3, and 11.

[0071] The n-type thermoelectric conversion element 6 is made of an alloy having a half-Heusler structure represented by the following formula (1) and having a negative Seebeck coefficient. A x B y NiSn···(1) [In formula (1), A is Ti or Zr, and when A is Ti, B is at least one of Hf and Zr, and when A is Zr, B is at least one of Hf and Ti, and 0.5≦x≦1, 0.0≦y≦0.5.]

[0072] More specifically, the n-type thermoelectric conversion element 6 is made of an alloy represented by any one of the following formulas (2) to (7) and having a half-Heusler structure with a negative Seebeck coefficient. Ti 1-a Hf a NiSn···(2) [In formula (2), 0.0≦a≦0.5.] Ti 1-b Zr b NiSn···(3) [In formula (3), 0.0≦b≦0.5.] Zr 1-c Hf c NiSn···(4) [In formula (4), 0.0≦c≦0.5.] Zr 1-d Ti d NiSn···(5) [In formula (5), 0.0≦d≦0.5.] Zr 1-e-f Ti e Hf f NiSn···(6) [In formula (6), 0.0≦e≦0.25 and 0.0≦f≦0.25.] Ti 1-g-h Zr g Hf h NiSn···(7) [In formula (7), 0.0≦g≦0.25 and 0.0≦h≦0.25.]

[0073] All of the alloys having the half-Heusler structure represented by formulas (2) to (7) have a negative Seebeck coefficient in the temperature range of 25°C to 500°C, and have excellent oxidation resistance in air in the temperature range of 500°C or lower.

[0074] The alloys having the half-Heusler structure represented by formulas (2) to (7) have an electrical resistivity of 5 mΩ·cm or less in the temperature range of 100°C to 500°C.

[0075] Therefore, the alloys having the half-Heusler structure represented by formulas (2) to (7) can exhibit excellent thermoelectric conversion performance as materials for the n-type thermoelectric conversion element 6 in the above temperature range.

[0076] 5 is a process diagram showing a method for manufacturing an n-type thermoelectric conversion element 6. Referring to FIG. 5, when the manufacture of the n-type thermoelectric conversion element 6 starts, raw materials are blended so that the element ratio is the same as the element ratio of the target alloy (step S1). The raw materials can be a simple metal, an intermetallic compound or solid solution composed of multiple component elements, or a composite (such as an alloy) of an intermetallic compound (or solid solution).

[0077] After step S1, the blended raw materials are melted and then cooled to produce an alloy having a half-Heusler structure (step S2). The method for melting the raw materials is not particularly limited, but arc melting, induction heating, and the like can be used. The melting temperature is higher than the melting points of the raw material phase and the product phase. Furthermore, the melting atmosphere is preferably a non-oxidizing atmosphere such as an inert gas atmosphere, such as helium or argon, a reduced pressure atmosphere, or a vacuum, to avoid oxidation of the raw materials.

[0078] After step S2, the alloy having a half-Heusler structure is heat-treated (step S3). The heat-treatment conditions vary depending on the type and amount of metal elements contained in the alloy, but it is preferable to heat-treat at a temperature of, for example, about 1000 to 1300°C. By heat-treating the alloy having a half-Heusler structure, a more homogeneous alloy can be produced, and its performance as a thermoelectric conversion material can be improved.

[0079] Alternatively, after step S2, instead of step S3, the alloy having the half-Heusler structure is pulverized, and the powder is pressure-molded to produce an alloy of any shape, which is then sintered (step S4). During sintering, uniaxial pressure application during heating, such as hot pressing and electric current sintering (so-called SPS (Spark Plasma Sintering) sintering), can produce a sintered body with high sintering density, resulting in a sintered body with low electrical resistivity and high fracture strength. Furthermore, solid-phase reactions are promoted, allowing a more homogeneous sintered body to be obtained in a short time. The sintering atmosphere is preferably a non-oxidizing atmosphere to avoid oxidation of the alloy having the half-Heusler structure.

[0080] After step S3 or step S4, the molten solidified material or sintered body is cut, ground, and polished to produce n-type thermoelectric conversion elements 6 (step S5). The size of the n-type thermoelectric conversion elements 6 can be determined based on the size and power generation amount of the thermoelectric conversion module 10, but generally, they are in the form of a square pillar with a side length of about 0.5 to 30 mm and a length of about 0.5 to 100 mm, or a cylinder with a diameter of about 0.5 to 30 mm and a length of about 0.5 to 100 mm. The completion of step S5 completes the manufacture of the n-type thermoelectric conversion elements 6.

[0081] In the process diagram shown in FIG. 5, step S5 may not be performed after step S4, and instead, in step S4, the powder before sintering may be press-molded to obtain the final shape and dimensions of the n-type thermoelectric conversion element 6, and then sintered.

[0082] In the process diagram shown in FIG. 5, when the n-type thermoelectric conversion element 6 is manufactured by steps S1, S2, S3, and S5, step S3 does not have to be performed.

[0083] The p-type thermoelectric conversion element 7 is made of an oxide represented by the following formula (8) or (9) and has a positive Seebeck coefficient at temperatures of 25° C. or higher. Ca 3-j Bi j Co4O9 (8) [In formula (8), 0.0≦j≦0.5.] Bi 2.0+k M 2.0+m Co2O9 (9) [In formula (9), M is at least one element selected from Ca and Sr, and −0.2≦k≦0.2 and −0.2≦m≦0.2.]

[0084] The oxide represented by formula (8) has a structure in which six oxygen elements (O) are octahedrally coordinated to one cobalt element (Co), and the CoO2 layers, in which the octahedra are two-dimensionally arranged so that they share edges, and layers having a rock-salt structure composed of Ca, Bi, Co, and O and having a composition ratio of (Ca,Bi)2CoO3, are stacked alternately.

[0085] The oxide represented by formula (9) has a structure in which six oxygen elements (O) are octahedrally coordinated to one cobalt element (Co), and the CoO2 layers, in which the octahedra are two-dimensionally arranged so that they share edges, and layers having a rock-salt structure with a composition ratio of Bi2M2O4, which is composed of Bi, M, and O, are alternately stacked.

[0086] Both oxides have a positive Seebeck coefficient and excellent oxidation resistance in the air in the temperature range of 25°C to 700°C. Furthermore, these oxides have an electrical resistivity of 15 mΩ·cm or less in the temperature range of 100°C to 700°C. Therefore, the oxides represented by formula (8) or formula (9) can exhibit excellent thermoelectric conversion performance as materials for p-type thermoelectric conversion element 7 in the above temperature range.

[0087] The oxide represented by formula (8) or formula (9) can be produced by known methods such as a single crystal production method, a powder production method, or a thin film production method.

[0088] Single crystal manufacturing methods include the flux method, zone melting method, pulling method, and glass annealing method via glass precursor, while powder manufacturing methods include the solid-state reaction method and sol-gel method, and thin film manufacturing methods include the sputtering method, laser ablation method, and chemical vapor deposition method.

[0089] Among the above manufacturing methods, the manufacturing method of oxides by the solid-state reaction method will be explained in more detail. The oxides represented by formula (8) or formula (9) are manufactured by mixing raw materials so that the elemental component ratio is similar to that of the target oxide, and then calcining the mixture.

[0090] The firing temperature and firing time are not particularly limited as long as they are conditions under which the desired oxide is formed, but for example, firing may be carried out at a temperature range of about 700 to 1000° C. for about 10 to 40 hours.

[0091] When carbonates or organic compounds are used as raw materials, it is preferable to calcinate the raw materials in advance to decompose them, and then calcinate them to form the desired oxide. For example, when carbonates are used as raw materials, calcination can be carried out at about 700 to 900°C for about 10 hours, followed by calcination under the above conditions.

[0092] The firing atmosphere is usually an oxidizing atmosphere such as an oxygen stream or air, but if the raw materials contain a sufficient amount of oxygen, firing may be performed in an inert atmosphere, for example. The amount of oxygen in the oxide produced can be controlled by the oxygen partial pressure during firing, the firing temperature, the firing time, etc., and the higher the oxygen partial pressure, the higher the oxygen ratio in formula (8) or (9).

[0093] To produce the desired oxide by the solid-state reaction method, it is preferable to press-form the raw material powder and sinter it to efficiently proceed with the solid-state reaction. The resulting sintered body is then cut, ground, and polished to form the p-type thermoelectric conversion element 7 to be used in the thermoelectric conversion module 10.

[0094] The size of the p-type thermoelectric conversion element 7 can be determined depending on the size of the thermoelectric conversion module 10, the amount of power generation, etc., but generally, it is sufficient if it is a square prism with a cross-sectional side of about 0.5 to 30 mm and a length of about 0.5 to 100 mm, or a cylinder with a diameter of about 0.5 to 30 mm and a length of about 0.5 to 100 mm.

[0095] In addition, in order to obtain the required shape without undergoing processing and molding after firing, the powder before sintering may be pre-molded into a shape and dimensions that will result in the element shape after sintering, and then sintered.

[0096] The raw materials are not particularly limited as long as they can form oxides upon firing, and include elemental metals, oxides, and various compounds (carbonates, etc.). Alkoxide compounds can be used as the Ca source and Co source. Examples of alkoxide compounds used as the Ca source include calcium oxide (CaO), calcium chloride (CaCl2), calcium carbonate (CaCO3), calcium nitrate (Ca(NO3)2), calcium hydroxide (Ca(OH)2), dimethoxycalcium (Ca(OCH3)2), diethoxycalcium (Ca(OC2H5)2), and dipropoxycalcium (Ca(OC3H7)2).

[0097] Alkoxide compounds used as Co sources include cobalt oxide (CoO, Co2O3, Co3O4), cobalt chloride (CoCl2), cobalt carbonate (CoCO3), cobalt nitrate (Co(NO3)2), cobalt hydroxide (Co(OH)2), and dipropoxycobalt (Co(OC3H7)2).

[0098] Similarly, for the other elements of the p-type thermoelectric conversion element 7, simple elements, oxides, chlorides, carbonates, nitrates, hydroxides, alkoxide compounds, and the like can be used.

[0099] The Ca source and the Co source may be compounds containing two or more of the constituent elements of the complex oxide that constitutes the p-type thermoelectric conversion element 7. For other elements, compounds containing two or more of the constituent elements of the complex oxide that constitutes the p-type thermoelectric conversion element 7 may also be used.

[0100] 6 is an exploded perspective view of another thermoelectric conversion module according to an embodiment of the present invention, which may be a thermoelectric conversion module 100 shown in FIG.

[0101] 6, the thermoelectric conversion module 100 includes extraction electrodes 101 and 117, conductive members 102 to 116, and 271 to 286, and p-type thermoelectric conversion elements 121, 122, 125, 126, 129, 130, 133, 134, 137, 138, 141, 142, 145, 146, 149, 150, 153, 154, 157, 158, 161, 162, 165, 166, 169, 170, 173, 174, 177, 178, 179, 200, 201, 202, 203, 204, 205, 206, 207, 208, 209, 300, 310, 311, 312, 313, 314, 315, 316, 317, 318, 320, 321, 322, 323, 324, 325, 326, 327, 328, 329, 330, 331, 332, 333, 334, 335, 336, 337, 338, 340, 341, 342, 345, 346, 349, 150, 153, 154, 157, 158, 161, 162, 165, 166, 169, 170, 173, 174, 175, 176, 78, 181, and 182, n-type thermoelectric conversion elements 123, 124, 127, 128, 131, 132, 135, 136, 139, 140, 143, 144, 147, 148, 151, 152, 155, 156, 159, 160, 163, 164, 167, 168, 171, 172, 175, 176, 179, 180, 183, and 184, connection layers 191 to 222 and 231 to 262, and an insulating substrate 290. The insulating substrate 290 is electrically insulating (the same applies hereinafter).

[0102] Conductive members 102 to 116 are represented by "conductive member 101+i (i=1 to 15)", and conductive members 271 to 286 are represented by "conductive member 270+j (j=1 to 16)".

[0103] The p-type thermoelectric conversion elements 121, 122, 125, 126, 129, 130, 133, 134, 137, 138, 141, 142, 145, 146, 149, 150, 153, 154, 157, 158, 161, 162, 165, 166, 169, 170, 173, 174, 177, 178, 181, and 182 are represented by "p-type thermoelectric conversion elements 120+4k-3, 120+4k-2 (k=1 to 16)"; N-type thermoelectric conversion elements 123, 124, 127, 128, 131, 132, 135, 136, 139, 140, 143, 144, 147, 148, 151, 152, 155, 156, 159, 160, 163, 164, 167, 168, 171, 172, 175, 176, 179, 180, 183, and 184 are represented by "n-type thermoelectric conversion elements 122+4k-3, 122+4k-2 (k=1 to 16)".

[0104] The connection layers 191 to 222 are expressed as "connection layers 190+2k-1, 190+2k (k=1 to 16)", and the connection layers 231 to 262 are expressed as "connection layers 230+2k-1, 230+2k (k=1 to 16)".

[0105] The p-type thermoelectric conversion elements 120+4k-3 and 120+4k-2 (k=1 to 16) and the n-type thermoelectric conversion elements 122+4k-3 and 122+4k-2 (k=1 to 16) are arranged, for example, in a grid pattern.

[0106] In this case, p-type thermoelectric conversion elements 121, 122, 125, 126, 129, 130, 133, 134, 137, 138, 141, 142, 145, 146, 149, 150, 153, 154, 157, 158, 161, 162, 165, 166, 169, 170, 173, 174, 177, 178, 181, and 182 are each divided into two p-type thermoelectric conversion elements 120+4k-3 and 120+4k-2 (k=1 to 16).

[0107] Furthermore, n-type thermoelectric conversion elements 123, 124, 127, 128, 131, 132, 135, 136, 139, 140, 143, 144, 147, 148, 151, 152, 155, 156, 159, 160, 163, 164, 167, 168, 171, 172, 175, 176, 179, 180, 183, and 184 are divided into two n-type thermoelectric conversion elements 122+4k-3 and 122+4k-2 (k=1 to 16), respectively.

[0108] Then, two p-type thermoelectric conversion elements 120+4k-3, 120+4k-2 are considered as one set of p-type thermoelectric conversion elements, and two n-type thermoelectric conversion elements 122+4k-3, 122+4k-2 are considered as one set of n-type thermoelectric conversion elements. The p-type thermoelectric conversion elements 120+4k-3, 120+4k-2 (k=1 to 16) and the n-type thermoelectric conversion elements 122+4k-3, 122+4k-2 (k=1 to 16) are arranged so that one set of p-type thermoelectric conversion elements and one set of n-type thermoelectric conversion elements are arranged alternately in the xy plane.

[0109] The connection layers 190+2k-1 (k = 1 to 16) are provided corresponding to the two p-type thermoelectric conversion elements 120+4k-3, 120+4k-2 (k = 1 to 16), respectively, and are bonded to one end of the two p-type thermoelectric conversion elements 120+4k-3, 120+4k-2 (k = 1 to 16) in the longitudinal direction (z-axis direction).

[0110] The connection layers 190+2k (k = 1 to 16) are provided corresponding to the two n-type thermoelectric conversion elements 122+4k-3, 122+4k-2 (k = 1 to 16), respectively, and are bonded to one end of the two n-type thermoelectric conversion elements 122+4k-3, 122+4k-2 (k = 1 to 16) in the longitudinal direction (z-axis direction).

[0111] The connection layers 230+2k-1 (k=1 to 16) are provided corresponding to the two p-type thermoelectric conversion elements 120+4k-3, 120+4k-2, respectively, and are bonded to the other ends of the two p-type thermoelectric conversion elements 120+4k-3, 120+4k-2 in the longitudinal direction (z-axis direction).

[0112] The connection layers 230+2k (k = 1 to 16) are provided corresponding to the two n-type thermoelectric conversion elements 122+4k-3, 122+4k-2 (k = 1 to 16), respectively, and are bonded to the other ends in the longitudinal direction (z-axis direction) of the two n-type thermoelectric conversion elements 122+4k-3, 122+4k-2 (k = 1 to 16).

[0113] A portion of the extraction electrode 101 is bonded to the connection layer 191. The conductive members 101+k (k=1 to 15) are bonded to the connection layers 190+2k (k=1 to 15) and 190+2k-1 (k=2 to 16), respectively. The extraction electrode 117 is bonded to the connection layer 222.

[0114] Conductive members 270+k (k=1 to 16) are arranged, for example, in a grid pattern on the xy plane on insulating substrate 290. Conductive members 270+k (k=1 to 16) are bonded to connecting layers 230+2k-1, 230+2k (k=1 to 16), respectively.

[0115] In this way, the thermoelectric conversion module 100 is configured such that a thermoelectric conversion element unit Unit1 consisting of two p-type thermoelectric conversion elements electrically connected in parallel and a thermoelectric conversion element unit Unit2 consisting of two n-type thermoelectric conversion elements electrically connected in parallel are alternately arranged between the extraction electrode 101 and the extraction electrode 117 and electrically connected in series between the extraction electrode 101 and the extraction electrode 117.

[0116] Each of the conductive members 102 to 116 and 271 to 286 is made of the same material as the conductive members 2, 3, and 11 described above.

[0117] Each of n-type thermoelectric conversion elements 123, 124, 127, 128, 131, 132, 135, 136, 139, 140, 143, 144, 147, 148, 151, 152, 155, 156, 159, 160, 163, 164, 167, 168, 171, 172, 175, 176, 179, 180, 183, and 184 is made of the same material as n-type thermoelectric conversion element 6 described above and is manufactured by the same method as n-type thermoelectric conversion element 6.

[0118] Each of p-type thermoelectric conversion elements 121, 122, 125, 126, 129, 130, 133, 134, 137, 138, 141, 142, 145, 146, 149, 150, 153, 154, 157, 158, 161, 162, 165, 166, 169, 170, 173, 174, 177, 178, 181, and 182 is made of the same material as p-type thermoelectric conversion element 7 described above and is manufactured by the same method as p-type thermoelectric conversion element 7.

[0119] Each of the connecting layers 191, 193, 195, 197, 199, 201, 203, 205, 207, 209, 211, 213, 215, 217, 219, 221, 231, 233, 235, 237, 239, 241, 243, 245, 247, 249, 251, 253, 255, 257, 259, and 261 is made of the same material as the connecting layers 5 and 9 described above. Each of the connecting layers 192, 194, 196, 198, 200, 202, 204, 206, 208, 210, 212, 214, 216, 218, 220, 222, 232, 234, 236, 238, 240, 242, 244, 246, 248, 250, 252, 254, 256, 258, 260, and 262 is made of the same material as the connecting layers 4 and 8 described above.

[0120] 7 is an exploded perspective view of yet another thermoelectric conversion module according to an embodiment of the present invention, which may be a thermoelectric conversion module 300 shown in FIG.

[0121] 7, thermoelectric conversion module 300 includes conductive members 301-315, 412-425, p-type thermoelectric conversion elements 321, 323, 325, 327, 329, 331, 333, 335, 337, 339, 341, 343, 345, 347, and 349, n-type thermoelectric conversion elements 322, 324, 326, 328, 330, 332, 334, 336, 338, 340, 342, 344, 346, 348, and 350, connection layers 351-410, extraction electrodes 411 and 426, and an insulating substrate 430. The term insulating substrate 430 means that it is electrically insulated (the same applies hereinafter).

[0122] Conductive members 301 to 315 are represented by "conductive member 300+i (i=1 to 15)", and conductive members 412 to 425 are represented by "conductive member 411+j (j=1 to 14)". The p-type thermoelectric conversion elements 321, 323, 325, 327, 329, 331, 333, 335, 337, 339, 341, 343, 345, 347, and 349 are represented by "p-type thermoelectric conversion element 320+2m-1 (m=1 to 15)", and the n-type thermoelectric conversion elements 322, 324, 326, 328, 330, 332, 334, 336, 338, 340, 342, 344, 346, 348, and 350 are represented by "n-type thermoelectric conversion element 320+2m (m=1 to 15)".

[0123] The connection layers 351 to 410 are represented by "connection layer 350+n (n=1 to 60)".

[0124] The p-type thermoelectric conversion elements 320+2m-1 (m = 1 to 15) and the n-type thermoelectric conversion elements 320+2m (m = 1 to 15) are arranged, for example, in a grid pattern on the xy plane. In this case, the p-type thermoelectric conversion elements 320+2m-1 (m = 1 to 15) and the n-type thermoelectric conversion elements 320+2m (m = 1 to 15) are arranged so that adjacent thermoelectric conversion elements have different conductivity types.

[0125] Connection layers 350+n (n = 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29) are provided corresponding to p-type thermoelectric conversion elements 320+2m-1 (m = 1 to 15), respectively, and are bonded to one end in the longitudinal direction (z-axis direction) of p-type thermoelectric conversion elements 320+2m-1 (m = 1, 3, 5, 7, 9, 11, 13, 15).

[0126] The connection layers 350+n (n=2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30) are provided corresponding to the n-type thermoelectric conversion elements 320+2m (m=1 to 15), respectively, and are bonded to one end in the longitudinal direction (z-axis direction) of the n-type thermoelectric conversion elements 320+2m (m=1 to 15).

[0127] Connection layers 350+n (n=31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59) are provided corresponding to p-type thermoelectric conversion elements 320+2m-1 (m=1 to 15), respectively, and are bonded to the other ends in the longitudinal direction (z-axis direction) of p-type thermoelectric conversion elements 320+2m-1 (m=1 to 15).

[0128] Connection layers 350+n (n=32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60) are provided corresponding to n-type thermoelectric conversion elements 320+2m (m=1 to 15), respectively, and are bonded to the other ends in the longitudinal direction (z-axis direction) of n-type thermoelectric conversion elements 320+2m (m=1 to 15).

[0129] The connection layers 300+i (i=1 to 15) are bonded to the connection layers 350+n and 351+n (n=1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, and 29), respectively.

[0130] The extraction electrodes 411 and 426 and the conductive members 412 to 425 are disposed on an insulating substrate 430. A portion of the extraction electrode 411 is adhered to the connection layer 381. The conductive members 411+j (j=1 to 14) are adhered to the connection layers 350+n and 351+n (n=32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58), respectively. The extraction electrode 426 is adhered to the connection layer 410.

[0131] Each of the conductive members 301 to 315 and 412 to 425 is made of the same material as the conductive members 2, 3 and 11 described above.

[0132] Each of n-type thermoelectric conversion elements 322, 324, 326, 328, 330, 332, 334, 336, 338, 340, 342, 344, 346, 348, and 350 is made of the same material as n-type thermoelectric conversion element 6 described above, and is manufactured by the same method as n-type thermoelectric conversion element 6.

[0133] Each of p-type thermoelectric conversion elements 321, 323, 325, 327, 329, 331, 333, 335, 337, 339, 341, 343, 345, 347, and 349 is made of the same material as p-type thermoelectric conversion element 7 described above, and is manufactured by the same method as p-type thermoelectric conversion element 7.

[0134] Each of the connecting layers 351, 353, 355, 357, 359, 361, 363, 365, 367, 369, 371, 373, 375, 377, 379, 381, 383, 385, 387, 389, 391, 393, 395, 397, 399, 401, 403, 405, 407, and 409 is made of the same material as the connecting layers 5 and 9 described above.

[0135] Each of the connecting layers 352, 354, 356, 358, 360, 362, 364, 366, 368, 370, 372, 374, 376, 378, 380, 382, ​​384, 386, 388, 390, 392, 394, 396, 398, 400, 402, 404, 406, 408, and 410 is made of the same material as the connecting layers 4 and 8 described above.

[0136] The thermoelectric conversion module 300 has a configuration in which p-type thermoelectric conversion elements 321, 323, 325, 327, 329, 331, 333, 335, 337, 339, 341, 343, 345, 347, 349 and n-type thermoelectric conversion elements 322, 324, 326, 328, 330, 332, 334, 336, 338, 340, 342, 344, 346, 348, 350 are electrically connected in series between the extraction electrodes 411, 426.

[0137] In the above, the method of applying the connecting layers 4, 5, 8, 9, 191 to 222, 231 to 262, and 351 to 310 is not particularly limited, but it is preferable to use a conventional printing technique such as screen printing to ensure a uniform thickness. Furthermore, the thickness of the applied layer is also not particularly limited, but to maintain good bonding strength, heat transfer, and electrical resistance, the applied thickness is preferably determined so that it is 5 to 80 μm after solidification, more preferably 10 to 50 μm after solidification.

[0138] As described above, the thermoelectric conversion module according to the embodiment of the present invention has a configuration in which p-type thermoelectric conversion elements and n-type thermoelectric conversion elements are electrically connected in series between two extraction electrodes by various methods. [Example]

[0139] Hereinafter, the thermoelectric conversion module according to the embodiment of the present invention will be described in detail using examples.

[0140] [Example of thermoelectric conversion element] (Examples 1 to 37) The composition formula is Ti 0.75 Hf 0.25 The n-type thermoelectric conversion material of Example 1, represented by NiSn, was prepared by the following method. First, granular titanium (Ti), hafnium (Hf), nickel (Ni), and tin (Sn) were weighed out so that the molar ratio of Ti:Hf:Ni:Sn was 0.75:0.25:1:1, and the mixture was completely melted by arc melting to obtain a master alloy. Next, the master alloy was pulverized into powder using a zirconia mortar and pestle.

[0141] 34 g of this powder was placed in a carbon mold with a diameter of 30 mm, and sintered in a vacuum at 1080°C for 5 minutes using an electric current sintering method under a uniaxial pressure of 30 MPa. The disc-shaped electric current sintered body with a diameter of approximately 30 mm was then polished to a thickness of 5 mm, and then cut so that the pressed surface was 3.5 mm x 3.5 mm, yielding a rectangular parallelepiped n-type thermoelectric conversion material with a length of 5 mm corresponding to the thickness direction of the disc.

[0142] In addition, for Examples 2 to 37, n-type thermoelectric conversion materials were obtained by manufacturing, processing and molding under the firing conditions and procedures described above, except that the element ratios were changed to obtain the compositions shown in Table 1-1 or Table 1-2.

[0143] (Comparative Example 1) The composition formula is CaMn 0.98 Mo 0.02An n-type thermoelectric conversion material represented by O3 was prepared by the following method: First, calcium carbonate (CaCO3), manganese oxide (Mn2O3), and molybdenum oxide (MoO3) were weighed out so that the molar ratio of Ca:Mn:Mo was 1:0.98:0.02, and then thoroughly mixed.

[0144] The resulting mixture was placed in an alumina crucible and fired at 800°C in air for 10 hours. The fired product was thoroughly mixed using an agate mortar and pestle. The powder was then molded into a disk approximately 20 mm in diameter and 2-10 mm thick. The molded body was placed on an alumina boat and fired at 1300°C in air for 20 hours. The resulting sintered body was then crushed using an agate mortar and pestle.

[0145] The obtained powder was processed and molded into a disk shape with a diameter of 40 mm and a thickness of 7 mm, and sintered in air at 1300°C for 20 hours. The obtained sintered body was ground and cut into a rectangular parallelepiped with a processed surface of 3.5 mm x 3.5 mm and a length corresponding to the thickness direction of 5 mm, to obtain an n-type thermoelectric conversion material.

[0146] [Test Example 1] For the n-type thermoelectric conversion elements obtained in Examples 1 to 37 and Comparative Example 1, the ZT values ​​were calculated by the following test.

[0147] The ZT value is calculated by the following formula: ZT=S 2 T / ρκ···(10) In equation (10), S is the Seebeck coefficient, T is the measurement temperature (absolute temperature), ρ is the electrical resistivity, and κ is the thermal conductivity.

[0148] The Seebeck coefficient Z was measured as follows. Two 0.1 mm diameter thermocouples (R-compatible thermocouples) made of a platinum-platinum-rhodium alloy were attached to both sides of an n-type thermoelectric material measuring 3.5 mm x 3.5 mm using silver paste. The n-type thermoelectric material was then placed in a tubular furnace and heated to temperatures between 100 and 700°C.

[0149] Then, one side of the n-type thermoelectric conversion element with the thermocouple attached was cooled by blowing air onto it, creating a temperature difference between the two sides of the n-type thermoelectric conversion element. This temperature difference and the thermoelectromotive force (voltage) generated at both ends of the n-type thermoelectric conversion element were then measured using the thermocouple. The thermoelectromotive force was measured using the platinum wire of the thermocouple.

[0150] The temperature difference was changed between approximately 1 and 7°C, and the temperature difference and thermoelectromotive force were measured at three to seven different points. The data consisting of the measured temperature difference and thermoelectromotive force were then plotted with the temperature difference on the horizontal axis and the thermoelectromotive force on the vertical axis, and a straight line was approximated using the least squares method. The slope of the straight line was calculated as the Seebeck coefficient S.

[0151] Electrical resistivity was measured using the DC four-terminal method. Platinum wires with a diameter of 0.05 mm were attached with silver paste to both sides of an n-type thermoelectric material with an area of ​​3.5 mm × 3.5 mm to serve as current leads for passing DC current during measurement. Two platinum wires with a diameter of 0.05 mm were also attached with silver paste to both sides of the n-type thermoelectric material with an area of ​​3.5 mm × 3.5 mm, parallel to each other and spaced approximately 2–3 mm apart, spanning the width (3.5 mm) of the n-type thermoelectric material. These served as voltage leads for measuring the voltage generated by passing current during measurement.

[0152] The sample was then placed in a tubular furnace, and while the temperature was raised in air, a current of approximately 0.05 to 100 mA was passed through the sample at regular time or temperature intervals, and the voltage at that time was measured. The electrical resistivity of the sample was calculated using the measured voltage, the current passed through the sample, and the sample shape using the following equation. ρ=(V×S S ) / (I×L) (11) In equation (11), V is the measured voltage and S S is the cross-sectional area of ​​the sample (3.5 mm × 3.5 mm in this test), I is the applied current, and L is the distance between the voltage leads (approximately 2 to 3 mm in this test).

[0153] The specific heat capacity C at room temperature in vacuum was measured using the laser flash method. p The thermal conductivity κ was calculated using the following equation: κ=C p ×α×d (12) After calculating the Seebeck coefficient S, the electrical resistivity ρ, and the thermal conductivity κ, the dimensionless figure of merit ZT was calculated by substituting the calculated Seebeck coefficient S, the electrical resistivity ρ, and the thermal conductivity κ, and the measurement temperature T (absolute temperature) into equation (10).

[0154] The Seebeck coefficient S, electrical resistivity ρ, thermal conductivity κ, and dimensionless figure of merit ZT at 500°C for Examples 1 to 31 are shown in Table 1-1. The Seebeck coefficient S, electrical resistivity ρ, thermal conductivity κ, and dimensionless figure of merit ZT at 500°C for Examples 32 to 37 are shown in Table 1-2. The Seebeck coefficient S, electrical resistivity ρ, thermal conductivity κ, and dimensionless figure of merit ZT at 500°C for Comparative Example 1 are shown in Table 1-3.

[0155] [Table 1-1]

[0156] [Table 1-2]

[0157] [Table 1-3]

[0158] In Table 1-1, the n-type thermoelectric conversion elements in Examples 1 to 6 have a half-Heusler structure represented by formula (2), the n-type thermoelectric conversion elements in Examples 7 to 10 have a half-Heusler structure represented by formula (3), the n-type thermoelectric conversion elements in Examples 11 to 14 have a half-Heusler structure represented by formula (4), the n-type thermoelectric conversion elements in Examples 15 to 18 have a half-Heusler structure represented by formula (5), and the n-type thermoelectric conversion elements in Examples 19 to 27 have a half-Heusler structure represented by formula (6). The n-type thermoelectric conversion elements in Examples 28 to 31 in Table 1-1 and Examples 32 to 37 in Table 1-2 have a half-Heusler structure represented by formula (7).

[0159] As shown in Tables 1-1 and 1-2, the n-type thermoelectric conversion elements in Examples 1 to 37 have a dimensionless figure of merit ZT greater than that of the n-type thermoelectric conversion element in Comparative Example 1 shown in Table 1-3. This is thought to be because the electrical resistivities of the n-type thermoelectric conversion elements in Examples 1 to 37 were 0.98 to 1.45 mΩcm, which was significantly lower (by one order of magnitude or more) than the electrical resistivity of 16.8 mΩcm in Comparative Example 1.

[0160] 8 is a graph showing the temperature dependence of the dimensionless figure of merit ZT in Example 1 and Comparative Example 1. In Fig. 8, the vertical axis represents the dimensionless figure of merit ZT, and the horizontal axis represents temperature. The black circles represent the relationship between the dimensionless figure of merit ZT and temperature for the n-type thermoelectric conversion element of Example 1, and the black triangles represent the relationship between the dimensionless figure of merit ZT and temperature for the n-type thermoelectric conversion element of Comparative Example 1.

[0161] 8, the dimensionless figure of merit ZT of the n-type thermoelectric conversion element in Example 1 increases with increasing temperature in the temperature range of 100 to 500° C. More specifically, the dimensionless figure of merit ZT of the n-type thermoelectric conversion element in Example 1 increases by about 2.7 times when the temperature increases from 100° C. to 300° C., and increases by about 3.6 times when the temperature increases from 100° C. to 500° C.

[0162] On the other hand, the rate of increase in the dimensionless figure of merit ZT of the n-type thermoelectric conversion element in Comparative Example 1 due to temperature increase is smaller in the temperature range of 100 to 500°C than the dimensionless figure of merit ZT of the n-type thermoelectric conversion element in Example 1. More specifically, the dimensionless figure of merit ZT of the n-type thermoelectric conversion element in Comparative Example 1 increases by about 1.3 times when the temperature increases from 100°C to 300°C, and increases by about 2.2 times when the temperature increases from 100°C to 500°C.

[0163] The dimensionless figure of merit ZT of the n-type thermoelectric conversion element in Example 1 is approximately 2.3 times the dimensionless figure of merit ZT of the n-type thermoelectric conversion element in Comparative Example 1 at a temperature of 100°C, approximately 4.9 times the dimensionless figure of merit ZT of the n-type thermoelectric conversion element in Comparative Example 1 at a temperature of 300°C, and approximately 3.7 times the dimensionless figure of merit ZT of the n-type thermoelectric conversion element in Comparative Example 1 at a temperature of 500°C.

[0164] As described above, the dimensionless figure of merit ZT of the n-type thermoelectric conversion element in Example 1 is 2.3 times or more the dimensionless figure of merit ZT of the n-type thermoelectric conversion element in Comparative Example 1 in the temperature range of 100 to 500°C. Therefore, it was found that the n-type thermoelectric conversion element in Example 1 has excellent thermoelectric conversion efficiency.

[0165] Fig. 9 is a diagram showing the relationship between the Seebeck coefficient and thermal conductivity for the n-type thermoelectric conversion elements of Examples 1, 3 to 6, 7 to 10, 19 to 27, 28 to 31, and 32 to 37. In Fig. 9, the vertical axis represents the absolute value of the Seebeck coefficient, and the horizontal axis represents thermal conductivity.

[0166] In FIG. 9, the line L1 is 1-a Hf a The figure shows the relationship between the Seebeck coefficient and the thermal conductivity in the n-type thermoelectric conversion elements of Examples 1 and 3 to 6, which are represented by the composition formula of NiSn (0.1≦a≦0.5). 1-b Zr b The figure shows the relationship between the Seebeck coefficient and the thermal conductivity in the n-type thermoelectric conversion elements of Examples 7 to 10, which are represented by the composition formula of NiSn (0.1≦b≦0.5). Line L3 indicates the relationship between the Seebeck coefficient and the thermal conductivity in the n-type thermoelectric conversion elements of Examples 7 to 10, which are represented by the composition formula of NiSn (0.1≦b≦0.5).1-e-f Ti e Hf f The figure shows the relationship between the Seebeck coefficient and the thermal conductivity in the n-type thermoelectric conversion elements of Examples 19 to 27, which are represented by the composition formula of NiSn (0.05≦e≦0.25, 0.05≦f≦0.25). Line L4 represents the relationship between the Seebeck coefficient and the thermal conductivity in the n-type thermoelectric conversion elements of Examples 19 to 27, which are represented by the composition formula of NiSn (0.05≦e≦0.25, 0.05≦f≦0.25). 1-e-f Zr e Hf f Line L5 shows the relationship between the Seebeck coefficient and the thermal conductivity in the n-type thermoelectric conversion elements of Examples 28 to 31, which are represented by the composition formula of NiSn (0.05≦e≦0.25, 0.05≦f≦0.25). 1-g-h Zr g Hf h 1 shows the relationship between the Seebeck coefficient and the thermal conductivity in the n-type thermoelectric conversion elements of Examples 32 to 37 represented by the composition formula NiSn (0.05≦g≦0.25, 0.05≦h≦0.25).

[0167] In the n-type thermoelectric conversion elements of Examples 1 and 3 to 6, the thermal conductivity tends to increase as the Ti content increases.

[0168] 9, the absolute value of the Seebeck coefficient increases with increasing thermal conductivity in the n-type thermoelectric conversion elements of Examples 1 and 3 to 6. When the absolute value of the Seebeck coefficient is y and the thermal conductivity is x, the relationship between x and y is expressed by the following equation. y=100x-361···(13)

[0169] The contribution ratio R of the regression line expressed by equation (13) 2 is 0.9381, and the correlation coefficient between x and y is (0.9381) 1 / 2 =0.97. As a result, the absolute value y of the Seebeck coefficient in the n-type thermoelectric conversion elements of Examples 1 and 3 to 6 has a strong correlation with the thermal conductivity x. Thus, the absolute value of the Seebeck coefficient in the n-type thermoelectric conversion elements of Examples 1 and 3 to 6 is characterized by increasing in proportion to the thermal conductivity.

[0170] The n-type thermoelectric conversion elements of Examples 1 and 3 to 6 were made of Ti 1-a Hf aSince it is expressed by the composition formula NiSn (0.1≦a≦0.5), Ti 1-a Hf a An n-type thermoelectric conversion element having a half-Heusler structure represented by the composition formula NiSn (0.1≦a≦0.5) is characterized in that the absolute value of the Seebeck coefficient increases in proportion to the thermal conductivity (see line L1).

[0171] The absolute value of the Seebeck coefficient increases with increasing thermal conductivity in the n-type thermoelectric conversion elements of Examples 7 to 10. Therefore, when the absolute value of the Seebeck coefficient is y and the thermal conductivity is x, the relationship between x and y is expressed by the following equation. y=112x-403···(14)

[0172] The contribution ratio R of the regression line expressed by equation (14) 2 is 0.6246, and the correlation coefficient between x and y is (0.6246) 1 / 2 =0.79. As a result, the absolute value y of the Seebeck coefficient in the n-type thermoelectric conversion elements of Examples 7 to 10 has a strong correlation with the thermal conductivity x. Therefore, the absolute value of the Seebeck coefficient in the n-type thermoelectric conversion elements of Examples 7 to 10 is characterized by increasing as the thermal conductivity increases.

[0173] The n-type thermoelectric conversion elements of Examples 7 to 10 were made of Ti 1-b Zr b Since it is expressed by the composition formula NiSn (0.1≦b≦0.5), Ti 1-b Zr b An n-type thermoelectric conversion element having a half-Heusler structure represented by the composition formula NiSn (0.1≦b≦0.5) is characterized in that the absolute value of the Seebeck coefficient increases with increasing thermal conductivity (see line L2).

[0174] The absolute value of the Seebeck coefficient decreases with increasing thermal conductivity in the n-type thermoelectric conversion elements of Examples 19 to 27. When the absolute value of the Seebeck coefficient is y and the thermal conductivity is x, the relationship between x and y is expressed by the following equation. y=-72x+475 (15)

[0175] The contribution ratio R of the regression line expressed by equation (15) 2 is 0.7091, and the correlation coefficient between x and y is (0.7091) 1 / 2 =0.84. As a result, the absolute value y of the Seebeck coefficient in the n-type thermoelectric conversion elements of Examples 19 to 27 correlates with the thermal conductivity x. Thus, the absolute value of the Seebeck coefficient in the n-type thermoelectric conversion elements of Examples 19 to 27 is characterized by decreasing as the thermal conductivity increases.

[0176] The n-type thermoelectric conversion elements of Examples 19 to 27 were made of Zr 1-e-f Ti e Hf f Since it is expressed by the composition formula NiSn (0.05≦e≦0.25, 0.05≦f≦0.25), Ti 1-e-f Zr e Hf f An n-type thermoelectric conversion element having a half-Heusler structure represented by the composition formula NiSn (0.05≦e≦0.25, 0.05≦f≦0.25) has the characteristic that the absolute value of the Seebeck coefficient decreases as the thermal conductivity increases (see line L3).

[0177] The absolute value of the Seebeck coefficient decreases with increasing thermal conductivity in the n-type thermoelectric conversion elements of Examples 28 to 31. When the absolute value of the Seebeck coefficient is y and the thermal conductivity is x, the relationship between x and y is expressed by the following equation. y=-71x+465 (16)

[0178] The contribution ratio R of the regression line expressed by equation (16) 2 is 0.9919, and the correlation coefficient between x and y is (0.9919) 1 / 2 =0.99. As a result, the absolute value y of the Seebeck coefficient in the n-type thermoelectric conversion elements of Examples 19 to 22 has a strong correlation with the thermal conductivity x.

[0179] Thus, the absolute value of the Seebeck coefficient in the n-type thermoelectric conversion elements of Examples 28 to 31 is characterized in that it decreases in proportion to the thermal conductivity.

[0180] The n-type thermoelectric conversion elements of Examples 28 to 31 were made of Ti 1-e-f Zr e Hf f Since it is expressed by the composition formula NiSn (0.05≦e≦0.25, 0.05≦f≦0.25), Ti 1-e-f Zr e Hf f An n-type thermoelectric conversion element having a half-Heusler structure represented by the composition formula NiSn (0.05≦e≦0.25, 0.05≦f≦0.25) has the characteristic that the absolute value of the Seebeck coefficient decreases in proportion to the thermal conductivity (see line L4).

[0181] The absolute value of the Seebeck coefficient decreases with increasing thermal conductivity in the n-type thermoelectric conversion elements of Examples 32 to 37. When the absolute value of the Seebeck coefficient is y and the thermal conductivity is x, the relationship between x and y is expressed by the following equation. y=-45x+356 (17)

[0182] The contribution ratio R of the regression line expressed by equation (17) 2 is 0.97, and the correlation coefficient between x and y is (0.97) 1 / 2 =0.98. As a result, the absolute value y of the Seebeck coefficient in the n-type thermoelectric conversion elements of Examples 32 to 37 has a strong correlation with the thermal conductivity x. Thus, the absolute value of the Seebeck coefficient in the n-type thermoelectric conversion elements of Examples 32 to 37 is characterized in that it decreases in proportion to the thermal conductivity.

[0183] The n-type thermoelectric conversion elements of Examples 32 to 37 were made of Ti 1-g-h Zr g Hf h Since it is expressed by the composition formula NiSn (0.05≦g≦0.25, 0.05≦h≦0.25), Ti 1-g-h Zr g Hf h An n-type thermoelectric conversion element having a half-Heusler structure represented by the composition formula NiSn (0.05≦g≦0.25, 0.05≦h≦0.25) has the characteristic that the absolute value of the Seebeck coefficient decreases in proportion to the thermal conductivity (see line L5).

[0184] [Example of thermoelectric conversion module] Example 38 The thermoelectric conversion module of Example 38 was produced by the following method.

[0185] [Fabrication of n-type thermoelectric conversion elements] Ti 0.75 Hf 0.25 An n-type thermoelectric conversion element represented by the composition formula NiSn was fabricated by the following method.

[0186] First, granular titanium (Ti), hafnium (Hf), nickel (Ni), and tin (Sn) were weighed out so that the molar ratio of Ti:Hf:Ni:Sn was 0.75:0.25:1:1, and then completely melted by arc melting to obtain a master alloy. The master alloy was then crushed into powder using a zirconia mortar and pestle.

[0187] 34 g of this powder was placed in a 30 mm diameter carbon mold and sintered in a vacuum at 1080°C for 5 minutes using an electric current sintering method under a uniaxial pressure of 30 MPa. The 30 mm diameter disk-shaped sintered body was then polished to a thickness of 5 mm, and the pressed surface was cut to 3.5 mm x 3.5 mm to obtain a rectangular n-type thermoelectric conversion element with a length corresponding to the thickness of 5 mm. The bonding surface with the conductive member was then made to have a size of 3.5 mm x 3.5 mm.

[0188] [Fabrication of p-type thermoelectric conversion elements] Ca 2.7 Bi 0.3 A p-type thermoelectric conversion element represented by the composition formula Co4O9 was fabricated by the following method.

[0189] First, calcium carbonate (CaCO3), bismuth oxide (Bi2O3), and cobalt oxide (Co3O4) were weighed and thoroughly mixed so that the molar ratio was Ca:Bi:Co = 2.7:0.3:4. The resulting mixture was then placed in an alumina crucible and fired at 800°C in air for 10 hours. The fired product was then thoroughly mixed using an agate mortar and pestle. This powder was then pressed into a disk approximately 20 mm in diameter and 2-10 mm thick. A gold sheet was placed on an alumina sheet, and the compact was then placed on top of that and fired at 860°C in air for 20 hours. The resulting sintered body was then crushed using an agate mortar and pestle.

[0190] The resulting powder was pressed into a disk shape with a diameter of 40 mm and a thickness of 5 mm, and hot-press sintered at 880°C for 20 hours in air under a uniaxial pressure of 10 MPa. The resulting hot-pressed sintered compact was polished and cut into a rectangular parallelepiped with a surface perpendicular to the pressing surface measuring 3.5 mm x 3.5 mm and a length of 5 mm, yielding a p-type thermoelectric conversion element. The bonding surface with the conductive member was then set to a surface measuring 3.5 mm x 3.5 mm.

[0191] [Preparation of silver paste] A commercially available silver paste (product name: MH-108A, silver content: 85 wt%) manufactured by Tanaka Kikinzoku Co., Ltd. was mixed with silver oxide (AgO), titanium oxide (TiO), and p-type thermoelectric oxide (Ca 2.7 Bi 0.3 The silver paste was prepared without adding any powder of Co4O9.

[0192] [Fabrication of thermoelectric conversion module] An aluminum oxide (alumina: Al2O3) plate measuring 3.5 mm x 7.5 mm and 0.8 mm thick was used as the insulating substrate, and a silver sheet measuring 3.2 mm x 7 mm and 0.1 mm thick was used as the conductive member.

[0193] Both junction surfaces of one p-type thermoelectric conversion element and both junction surfaces of one n-type thermoelectric conversion element were irradiated with ultraviolet light from a mercury lamp for 30 minutes.

[0194] The silver paste prepared by the above method was applied to the joining surface of the silver sheet. Here, the thickness of the conductive paste before solidification was adjusted using screen printing so that the thickness after solidification would be 10 μm.

[0195] The bonding surface of the silver sheet coated with silver paste was placed on one of the bonding surfaces of the p-type thermoelectric element and the n-type thermoelectric element, and the silver sheet was adhered to one of the bonding surfaces of the p-type thermoelectric element and the n-type thermoelectric element, thereby connecting one of the bonding surfaces of the p-type thermoelectric element and one of the bonding surfaces of the n-type thermoelectric element. In this case, the gap between the p-type thermoelectric element and the n-type thermoelectric element was set to 0.5 mm.

[0196] Two silver sheets measuring 3.2 mm x 20 mm and 0.1 mm thick were used, and the above silver paste was applied to a region 3.5 mm long from one end of the silver sheet using the above method.

[0197] One of the two silver sheets coated with silver paste was then bonded to the other joint surface of the p-type thermoelectric element, and the other silver sheet was bonded to the other joint surface of the n-type thermoelectric element, connecting the two extraction electrodes to the p-type and n-type thermoelectric elements. The two extraction electrodes were then placed on an insulating substrate to produce a precursor for the thermoelectric conversion module.

[0198] The thermoelectric conversion module precursor was then placed in a dryer and heated at 100°C for 30 minutes. It was then placed in a hot press furnace heated in air under uniaxial pressure. While applying a uniaxial pressure of 2.4 MPa to the bonding surface, the temperature was increased from room temperature to 200°C over 1 hour and held at 200°C for 1 hour. The pressure was then increased to 4.8 MPa, the temperature was increased to 450°C over 1 hour, held at 450°C for 1 hour and then raised to 800°C over 2 hours. In this case, the pressure was increased to 9.6 MPa when the temperature reached 625°C 1 hour after the start of the temperature increase. The pressure was then maintained while the mixture was fired at 800°C for 30 minutes. The pressure was then stopped and the mixture was allowed to cool naturally in the furnace, resulting in the thermoelectric conversion module of Example 38. This heat treatment bonded the silver sheet (extraction electrode) and the alumina substrate (insulating substrate) together.

[0199] Example 39 The thermoelectric conversion module of Example 39 was produced by the following method.

[0200] [Preparation of silver paste] A silver paste was prepared using a commercially available silver paste (product name: MH-108A, silver content: 85 wt%) manufactured by Tanaka Kikinzoku Co., Ltd. This silver paste consisted of 85 wt% silver powder (particle size: 0.1-5 μm), 1 wt% borosilicate bismuth glass, 5 wt% ethyl cellulose, 4 wt% terpineol, and 5 wt% butyl carbitol acetate. The wet silver paste was taken as 100 wt%. Silver oxide (AgO) powder was then sieved using a 38 μm (JIS standard 390 mesh) sieve. 0.5 wt% of the silver oxide (AgO) powder that passed through the sieve was added and thoroughly kneaded to obtain a silver paste.

[0201] A thermoelectric conversion module of Example 39 was produced in the same manner as in Example 38, except that the silver paste was prepared by the method described above.

[0202] (Examples 40 to 247) As shown in Tables 2-1 to 2-14, the thermoelectric conversion modules in Examples 40 to 247 were produced using the same junction forming method and manufacturing conditions as in Example 39, although the compositions, firing conditions, and shapes of the p-type and n-type thermoelectric conversion elements, the material and shape of the conductive members, and the compositions and amounts of additives added to the silver paste were different.

[0203] The thermoelectric conversion modules fabricated in Examples 38 to 247 have the same structure as the thermoelectric conversion module 10 shown in Figs. 1 to 4. In addition to silver oxide (AgO), titanium oxide (TiO) and p-type thermoelectric oxide (CaO) were also added as additives to the silver paste. 2.7 Bi 0.3 Titanium dioxide (TiO2) and p-type thermoelectric oxide (CaO) that had passed through a 38 μm sieve were used. 2.7Bi 0.3 Co4O9) powder was added in an amount of 0.5 to 10% by weight, with the wet state of the silver paste being 100% by weight, and the mixture was thoroughly kneaded.

[0204] (Comparative Example 2) As an n-type thermoelectric conversion element, CaMn 0.98 Mo 0.02 A thermoelectric conversion module in Comparative Example 2 was produced in the same manner as in Example 38, except that O3 was used.

[0205] (Comparative Examples 3 to 9) As an n-type thermoelectric conversion element, CaMn 0.98 Mo 0.02 Thermoelectric conversion modules in Comparative Examples 3 to 9 were produced in the same manner as in Example 39, except that O3 was used, as shown in Table 2-15.

[0206] [Test Example 2] For the thermoelectric conversion modules in Examples 38 to 247 and Comparative Examples 2 to 9, a plate-type electric furnace was used to heat the aluminum oxide substrate surface to which the thermoelectric conversion element was connected in air to 100 to 500°C, and the power extraction member (extraction electrode) on the opposite end was cooled in a copper jacket with its surface electrically insulated with polyimide tape and through which 20°C water was circulated, thereby creating a temperature difference.

[0207] The extraction electrodes placed on the low-temperature side of the p-type thermoelectric conversion element and the n-type thermoelectric conversion element were connected to an electrical load device, and the current and voltage were measured while changing the external load resistance, thereby obtaining the internal resistance and output of the thermoelectric conversion module.

[0208] Fig. 10 is a diagram showing the relationship between voltage, power generation output, and current in a thermoelectric conversion module. In Fig. 10, the vertical axis represents voltage and power generation output, and the horizontal axis represents current. Also, a straight line represents the relationship between voltage and current, and a curved line represents the relationship between power generation output and current.

[0209] 10, the voltage is proportional to the current, and the slope of the line showing the relationship between the voltage and the current indicates the internal resistance of the thermoelectric conversion module.

[0210] Power output is the product of voltage and current. As a result, the relationship between power output and current is expressed by an upwardly convex quadratic function. Therefore, a regression curve (quadratic curve) between power output and current was determined, and the maximum value of the quadratic curve was taken as the maximum power output.

[0211] The thermoelectric conversion module exhibits maximum output when the external load resistance matches the internal resistance, and when calculated using a regression curve, maximum output was also obtained at the point where the external load resistance matched the internal resistance.

[0212] 11 is a diagram showing the relationship between maximum output and heating temperature in Examples 38 and 39 and Comparative Example 2. In Fig. 11, the vertical axis represents maximum output, and the horizontal axis represents heating temperature. The black squares represent the relationship between maximum output and heating temperature in Example 38, the black circles represent the relationship between maximum output and heating temperature in Example 39, and the black triangles represent the relationship between maximum output and heating temperature in Comparative Example 2.

[0213] 11, the maximum output of the thermoelectric conversion module in Example 38 is greater than the maximum output of the thermoelectric conversion module in Comparative Example 2 in the temperature range of 100°C to 500°C. Moreover, the maximum output of the thermoelectric conversion module in Example 39 is greater than the maximum output of the thermoelectric conversion module in Example 38 in the temperature range of 100°C to 500°C.

[0214] The thermoelectric conversion module in Comparative Example 2 was made of CaMn 0.98 Mo 0.02 The thermoelectric conversion element is made of an n-type oxide represented by the composition formula O3, and the thermoelectric conversion element is made of silver oxide (Ag2O), titanium oxide (TiO2), and p-type thermoelectric oxide (Ca 2.7 Bi 0.3 This thermoelectric conversion module was fabricated using silver paste containing no Co4O9.

[0215] The thermoelectric conversion module in Example 38 is made of Ti 0.75 Hf 0.25The n-type thermoelectric conversion element with a half-Heusler structure represented by the composition formula of NiSn and the p-type thermoelectric oxides (Ca, Ag, Ti, and AgO) were used. 2.7 Bi 0.3 This thermoelectric conversion module was fabricated using silver paste containing no Co4O9.

[0216] The thermoelectric conversion module in Example 39 is made of Ti 0.75 Hf 0.25 This thermoelectric conversion module was fabricated using an n-type thermoelectric conversion element with a half-Heusler structure represented by the composition formula NiSn and silver paste with added silver oxide (Ag2O).

[0217] As a result, it was found that the use of n-type thermoelectric conversion elements with a half-Heusler structure improved the maximum output of the thermoelectric conversion module in the temperature range of 100°C to 500°C (see Example 38 and Comparative Example 2). It was also found that the use of silver paste containing silver oxide (AgO) further improved the maximum output of the thermoelectric conversion module in the temperature range of 100°C to 500°C (see Examples 38 and 39).

[0218] Therefore, the maximum output of a thermoelectric conversion module in which both the n-type and p-type thermoelectric conversion elements are made of thermoelectric oxide materials can be improved by changing the n-type thermoelectric conversion elements to n-type thermoelectric conversion elements with a half-Heusler structure, and the maximum output of a thermoelectric conversion module can be further improved by changing the silver paste of a thermoelectric conversion module equipped with n-type thermoelectric conversion elements with a half-Heusler structure to silver paste with added silver oxide (AgO).

[0219] The open circuit voltage, internal resistance and maximum output when the heating temperature of the thermoelectric conversion modules in Examples 38 to 247 and Comparative Examples 2 to 9 was 500° C. are shown in Tables 2-1 to 2-15.

[0220] [Table 2-1]

[0221]

Table 2-2

[0222]

Table 2-3

[0223]

Table 2-4

[0224]

Table 2-5

[0225]

Table 2-6

[0226]

Table 2-7

[0227]

Table 2-8

[0228]

Table 2-9

[0229]

Table 2-10

[0230]

Table 2-11

[0231] [Table 2-12]

[0232] [Table 2-13]

[0233] [Table 2-14]

[0234] [Table 2-15]

[0235] The thermoelectric conversion modules in Examples 38 to 123 are thermoelectric conversion modules equipped with n-type thermoelectric conversion elements having a half-Heusler structure represented by the composition formula of formula (2). The thermoelectric conversion modules in Examples 124 to 140 are thermoelectric conversion modules equipped with n-type thermoelectric conversion elements having a half-Heusler structure represented by the composition formula of formula (3). The thermoelectric conversion modules in Examples 141 to 150 are thermoelectric conversion modules equipped with n-type thermoelectric conversion elements having a half-Heusler structure represented by the composition formula of formula (4). The thermoelectric conversion modules in Examples 151 to 177 are thermoelectric conversion modules equipped with n-type thermoelectric conversion elements having a half-Heusler structure represented by the composition formula of formula (5). The thermoelectric conversion modules in Examples 178 to 212 are thermoelectric conversion modules equipped with n-type thermoelectric conversion elements having a half-Heusler structure represented by the composition formula of formula (6). Furthermore, the thermoelectric conversion modules in Examples 213 to 247 are thermoelectric conversion modules equipped with n-type thermoelectric conversion elements having a half-Heusler structure represented by the composition formula of formula (7).

[0236] In the thermoelectric conversion modules of Examples 39 to 247, the silver paste for connecting the n-type thermoelectric conversion element and the conductive member contains a component (additive) consisting of at least one of titanium oxide and silver oxide, and the silver paste for connecting the p-type thermoelectric conversion element and the conductive member contains a component (additive) consisting of at least one of titanium oxide and silver oxide, or an oxide used in the p-type thermoelectric conversion element.

[0237] Furthermore, in the thermoelectric conversion modules of Examples 62 to 98, 102 to 104, 107 to 112, 115 to 120, 126 to 130, 133 to 137, 144 to 148, 153 to 157, 160 to 164, 169 to 173, 182 to 186, 195 to 199, 205 to 209, 217 to 221, 230 to 234, and 240 to 244, the silver paste for connecting the n-type thermoelectric conversion element and the conductive member contains a component (additive) different from that of the silver paste for connecting the p-type thermoelectric conversion element and the conductive member.

[0238] Furthermore, in the thermoelectric conversion modules of Examples 39 to 61, 99 to 101, 105, 106, 113, 114, 121 to 125, 131, 132, 138 to 143, 149 to 152, 158, 159, 165 to 168, 174 to 181, 187 to 194, 200 to 204, 210 to 216, 222 to 229, 235 to 239, and 245 to 247, the silver paste for connecting the n-type thermoelectric conversion element and the conductive member is characterized by containing the same components (additives) as the silver paste for connecting the p-type thermoelectric conversion element and the conductive member.

[0239] The internal resistance of the thermoelectric conversion modules in Examples 38 to 247 is smaller than the internal resistance of the thermoelectric conversion modules in Comparative Examples 2 to 9. More specifically, the internal resistance of the thermoelectric conversion module in Example 38, 0.0510Ω, is smaller than the internal resistance of the thermoelectric conversion modules in Comparative Examples 2 to 9, 0.0996 to 0.194Ω, and the internal resistance of the thermoelectric conversion modules in Examples 39 to 247, 0.0284 to 0.0473Ω, is smaller than the internal resistance of the thermoelectric conversion module in Example 38, 0.0510Ω.

[0240] The silver paste of the thermoelectric conversion module in Example 38 was composed of silver oxide (Ag2O), titanium oxide (TiO2), and thermoelectric oxide (Ca 2.7 Bi 0.3 Since neither CaMnO nor CoO was added, the internal resistance of the thermoelectric conversion module in Example 38 was smaller than the internal resistance of the thermoelectric conversion modules in Comparative Examples 2 to 9. This is because the electrical resistivity of the n-type thermoelectric conversion element (n-type thermoelectric conversion element with a half-Heusler structure) used in the thermoelectric conversion module in Example 38 was CaMn 0.98 Mo 0.02 This is due to the fact that the electrical resistivity is lower than that of O3. Therefore, it was found that the characteristics of the thermoelectric conversion module in Example 38 made it possible to lower the internal resistance and improve the maximum output.

[0241] In addition, in the thermoelectric conversion modules in Examples 39 to 247, silver oxide (Ag2O), titanium oxide (TiO2), and thermoelectric oxide (Ca 2.7 Bi 0.3 Since silver paste containing additives such as silver oxide (AgO), titanium oxide (TiO), and thermoelectric oxide (CaO) was used, the internal resistance of the thermoelectric conversion modules in Examples 39 to 247 was smaller than that of the thermoelectric conversion module in Example 38. 2.7 Bi 0.3 This means that the problem is caused by using silver paste containing additives such as Co4O9.

[0242] Therefore, the properties of the thermoelectric conversion modules in Examples 39 to 247 indicate that silver oxide (AgO), titanium oxide (TiO), and thermoelectric oxide (Ca 2.7 Bi 0.3 It was found that the maximum output of the thermoelectric conversion module can be improved by using silver paste containing additives such as Co4O9.

[0243] The maximum outputs of the thermoelectric conversion modules in Comparative Examples 3 to 6, 8, and 9 were 64.8 mW, 50.0 mW, 74.6 mW, 52.1 mW, 58.0 mW, and 63.5 mW, respectively, and the maximum output of the thermoelectric conversion module in Comparative Example 2 was 64.2 mW. The thermoelectric conversion module in Comparative Example 2 used silver paste without additives, while the thermoelectric conversion modules in Comparative Examples 3 to 6, 8, and 9 used silver paste with additives. As a result, the maximum outputs of the thermoelectric conversion modules in Comparative Examples 3 to 6, 8, and 9, which were fabricated using silver paste with additives, were 1.01 times, 0.78 times, 1.16 times, 0.81 times, 0.90 times, and 0.99 times, respectively, of the maximum output of the thermoelectric conversion module in Comparative Example 2, which was fabricated using silver paste without additives.

[0244] On the other hand, the thermoelectric conversion modules in Examples 39, 41, 49, 51, 75, and 89 were made of the same silver paste (with the same additives (AgO, TiO, Ca)) as the silver paste in the thermoelectric conversion modules in Comparative Examples 3 to 6, 8, and 9, respectively. 2.7 Bi 0.3 The thermoelectric conversion modules were fabricated using a silver paste containing an equal amount of either Co4O9 or Co4O9. The maximum outputs of the thermoelectric conversion modules in Examples 39, 41, 49, 51, 75, and 89 were 135 mW, 126 mW, 135 mW, 139 mW, 141 mW, and 132 mW, respectively. The maximum output of the thermoelectric conversion module in Example 38, which was fabricated using a silver paste without an additive, was 99 mW. As a result, the maximum outputs of the thermoelectric conversion modules in Examples 39, 41, 49, 51, 75, and 89, which were fabricated using a silver paste with an additive, were 1.36 times, 1.27 times, 1.36 times, 1.40 times, 1.42 times, and 1.33 times, respectively, of the maximum output of the thermoelectric conversion module in Example 38, which was fabricated using a silver paste without an additive.

[0245] Thus, in Examples 39, 41, 49, 51, 75, and 89, Ti with a half-Heusler structure was used as a material for n-type thermoelectric conversion elements. 0.98 Hf 0.02The effect of combining NiSn and silver paste with additives was 1.27 to 1.42 times, whereas in Comparative Examples 3 to 6, 8, and 9, the effect of using the thermoelectric oxide material (CaMn 0.98 Mo 0.02 The effect of combining O3) with silver paste containing additives is 0.78 to 1.16 times.

[0246] Therefore, Ti with a half-Heusler structure is suitable as a material for n-type thermoelectric conversion elements. 0.98 Hf 0.02 It was found that the combination of NiSn and silver paste with additives is effective in improving the maximum output of thermoelectric conversion modules.

[0247] Thus, Ti with a half-Heusler structure is suitable as a material for n-type thermoelectric conversion elements. 0.98 Hf 0.02 The reason why the effect of combining NiSn and silver paste with additives is great is that, as shown in Tables 1-1 and 1-2, ZT of n-type thermoelectric conversion elements having a half-Heusler structure (n-type thermoelectric conversion elements of Examples 1 to 37) is higher than that of CaMn 0.98 Mo 0.02 This is because the ZT is higher than that of O3.

[0248] The thermoelectric conversion modules of Examples 42 to 44, 52 to 54, 64 to 66, 76 to 78, and 89, 91, and 92 are thermoelectric conversion modules that use silver, platinum, and gold as the conductive member, respectively, and the thermoelectric conversion modules of Examples 45, 46, 55, and 56, 67, 68, 79, 80, and 93, 94 are thermoelectric conversion modules that use LaNiO sintered body and RuO sintered body as the conductive member, respectively. The maximum output of the thermoelectric conversion modules of Examples 42 to 44, 52 to 54, 64 to 66, 76 to 78, and 89, 91, and 92 is greater than the maximum output of the thermoelectric conversion modules of Examples 45, 46, 55, and 56, 67, 68, 79, 80, and 93, 94, respectively.

[0249] Therefore, it is preferable to use any one of gold, silver and platinum as the conductive member.

[0250] The thermoelectric conversion modules of Examples 42, 52, 64, 76, and 90 are thermoelectric conversion modules in which the area of ​​the surface of the p-type thermoelectric conversion element parallel to the contact surface with the conductive member is larger than the area of ​​the surface of the n-type thermoelectric conversion element parallel to the contact surface with the conductive member. The thermoelectric conversion modules of Examples 41, 51, 63, 75, and 89 are thermoelectric conversion modules in which the area of ​​the surface of the p-type thermoelectric conversion element parallel to the contact surface with the conductive member is the same as the area of ​​the surface of the n-type thermoelectric conversion element parallel to the contact surface with the conductive member. The maximum output of the thermoelectric conversion modules of Examples 42, 52, 64, 76, and 90 is greater than the maximum output of the thermoelectric conversion modules of Examples 41, 51, 63, 75, and 89. Note that the comparison between the thermoelectric conversion modules of Examples 41, 51, 63, 75, and 89 and the thermoelectric conversion modules of Examples 42, 52, 64, 76, and 90 is between thermoelectric conversion modules using the same silver paste. Therefore, the area of ​​the surface of the p-type thermoelectric conversion element parallel to the contact surface with the conductive member is preferably larger than the area of ​​the surface of the n-type thermoelectric conversion element parallel to the contact surface with the conductive member.

[0251] As described above, the maximum output of the thermoelectric conversion module can be improved by using an n-type thermoelectric conversion element having a half-Heusler structure and a composition formula represented by any one of formulas (2) to (7).

[0252] Example 248 A thermoelectric conversion module of Example 248 was produced in the same manner as the thermoelectric conversion module of Example 38, except that the p-type thermoelectric conversion element was produced as follows.

[0253] [Fabrication of p-type thermoelectric conversion elements] A p-type thermoelectric conversion material with the composition formula Bi2Sr2Co2O9 was prepared by the following method: First, bismuth oxide (Bi2O3), strontium carbonate (SrCO3), and cobalt oxide (Co3O4) were weighed out so that the molar ratio of Bi:Sr:Co was 2:2:2, and then thoroughly mixed.

[0254] The resulting mixture was placed in an alumina crucible and fired at 800°C in air for 10 hours. The fired product was thoroughly mixed using an agate mortar and pestle. This powder was pressed into a disk approximately 20 mm in diameter and 2-10 mm thick. A gold sheet was placed in an alumina boat, and the molded body was placed on top of the gold sheet and fired at 840°C in air for 20 hours. The resulting sintered body was then crushed using an agate mortar and pestle.

[0255] The resulting powder was pressed into a disk shape with a diameter of 40 mm and a thickness of 5 mm, and hot-press sintered under a uniaxial pressure of 10 MPa at 860°C in air for 20 hours. The resulting hot-pressed sintered compact was ground and cut into a rectangular parallelepiped with a surface perpendicular to the pressed surface measuring 3.5 mm x 3.5 mm and a length of 5 mm, yielding a p-type thermoelectric conversion material. The joining surface was a 3.5 mm x 3.5 mm surface.

[0256] [Fabrication of thermoelectric conversion module] A thermoelectric conversion module of Example 248 was produced under the same conditions and by the same method as in Example 38, except that the material of the p-type thermoelectric conversion element was different.

[0257] (Example 249) A thermoelectric conversion module of Example 249 was produced in the same manner as in Example 248, except that a silver paste containing an additive was used.

[0258] (Examples 250 to 270) The composition, firing conditions, and shape of the thermoelectric conversion material, the composition and shape of the conductive member, and the composition and amount of additives added to the silver paste were different as shown in Table 3-1 or Table 3-2, but the junction formation method and manufacturing conditions were the same as those in Example 249, and thermoelectric conversion modules in Examples 250 to 270 were produced.

[0259] (Comparative Example 10) As an n-type thermoelectric conversion element, CaMn 0.98 Mo 0.02 A thermoelectric conversion module in Comparative Example 10 was produced in the same manner as in Example 248, except that O3 was used.

[0260] (Comparative Examples 11 to 17) CaMn 0.98 Mo 0.02 Thermoelectric conversion modules in Comparative Examples 11 to 17 were produced as shown in Table 3-3 in the same manner as in Example 249, except that an n-type thermoelectric conversion element made of O3 was used.

[0261] For the thermoelectric conversion modules of Examples 248 to 270 and Comparative Examples 10 to 17, the open circuit voltage, internal resistance, and maximum output were measured in accordance with Test Example 2 above.

[0262] The open circuit voltage, internal resistance and maximum output when the heating temperature of the thermoelectric conversion modules in Examples 248 to 270 and Comparative Examples 10 to 17 was 500° C. are shown in Tables 3-1 to 3-3.

[0263] [Table 3-1]

[0264] [Table 3-2]

[0265] [Table 3-3]

[0266] The thermoelectric conversion modules of Examples 248 to 270 are thermoelectric conversion modules equipped with n-type thermoelectric conversion elements having a half-Heusler structure represented by the composition formula of formula (2).

[0267] In the thermoelectric conversion modules of Example 248 and Comparative Example 10, the silver paste for connecting the n-type thermoelectric conversion elements and the conductive members does not contain any of titanium oxide, silver oxide, and oxides used in p-type thermoelectric conversion elements.

[0268] The maximum output of the thermoelectric conversion module of Example 248 is greater than the maximum output of the thermoelectric conversion module of Comparative Example 10.

[0269] Therefore, Bi is used as a material for p-type thermoelectric conversion elements. 2.2 Sr 2.2 Even when Co2O9 is used, Ti with a half-Heusler structure is used as the material for the n-type thermoelectric conversion element. 0.75 Hf 0.25 It was found that the use of NiSn can improve the maximum output of the thermoelectric conversion module.

[0270] In the thermoelectric conversion modules of Examples 249 to 270, the silver paste for connecting the n-type thermoelectric conversion element and the conductive member contains a component (additive) consisting of at least one of titanium oxide and silver oxide, and the silver paste for connecting the p-type thermoelectric conversion element and the conductive member contains a component (additive) consisting of at least one of titanium oxide and silver oxide, or an oxide used in the p-type thermoelectric conversion element.

[0271] Furthermore, in the thermoelectric conversion modules of Examples 257 to 268, the silver paste for connecting the n-type thermoelectric conversion element and the conductive member is characterized by containing a component (additive) different from that of the silver paste for connecting the p-type thermoelectric conversion element and the conductive member.

[0272] Furthermore, in the thermoelectric conversion modules of Examples 248 to 256, 269, and 270, the silver paste for connecting the n-type thermoelectric conversion element and the conductive member is characterized by containing the same components (additives) as the silver paste for connecting the p-type thermoelectric conversion element and the conductive member.

[0273] The maximum output of the thermoelectric conversion module of Example 248, 88.0 mW, is greater than the maximum outputs of the thermoelectric conversion modules of Comparative Examples 2 to 9, 50.0 to 74.6 mW, shown in Table 2-15. Therefore, even when a thermoelectric oxide material having the composition formula of Bi2Sr2Co2O9 is applied to a p-type thermoelectric conversion element, it is possible to obtain a p-type thermoelectric conversion element having a half-Heusler structure (Ti 0.75 Hf 0.25 It was found that the maximum output of the thermoelectric conversion module can be improved by using NiSn.

[0274] As shown in Tables 3-1 and 3-2, the maximum outputs of the thermoelectric conversion modules of Examples 249 to 270, 91.4 to 124 mW, were greater than the maximum output of 88.0 mW of the thermoelectric conversion module of Example 248. This is because the use of silver paste containing additives (Ag2O, TiO2, Bi2Sr2Co2O9, or a combination thereof) reduced the electrical resistance at the junctions between the n-type and p-type thermoelectric conversion elements and the conductive member (silver sheet). Therefore, it was found that the maximum output of the thermoelectric conversion module of Example 248 could be improved by changing the silver paste of the thermoelectric conversion module of Example 248 to silver paste containing additives (Ag2O, TiO2, Bi2Sr2Co2O9, or a combination thereof).

[0275] Furthermore, the maximum outputs of the thermoelectric conversion modules of Examples 249 to 270, 91.4 to 124 mW, are greater than the maximum outputs of the thermoelectric conversion modules of Comparative Examples 10 to 17, 31.0 to 49.9 mW. This is because the thermoelectric conversion modules of Examples 249 to 270 use n-type thermoelectric conversion elements (Ti 0.75 Hf 0.25 This is because the thermoelectric conversion modules of Comparative Examples 10 to 17 differ in that they use a p-type thermoelectric conversion element and silver paste. 0.75 Hf 0.25 It was found that the maximum output of the thermoelectric conversion module can be improved by constructing an n-type thermoelectric conversion element using NiSn. This is because the ZT of the n-type thermoelectric generation element with a half-Heusler structure is higher than that of CaMn 0.98Mo 0.02 This is because the ZT is higher than that of O3.

[0276] In Examples 248 to 270 described above, it was shown that the maximum output was improved for a thermoelectric conversion module using an n-type thermoelectric conversion element having a half-Heusler structure represented by the composition formula shown in Formula (2) above. However, similar improvements in maximum output can also be achieved for a thermoelectric conversion module using an n-type thermoelectric conversion element having a half-Heusler structure represented by any of the composition formulas shown in Formulas (3) to (7) above. This is because, as shown in Tables 1-1 to 1-3, the n-type thermoelectric conversion elements having a half-Heusler structure of Examples 1 to 37 have a larger ZT than the n-type thermoelectric conversion element of Comparative Example 1. Therefore, if experimental data are shown to demonstrate that the maximum output is improved for a thermoelectric conversion module using an n-type thermoelectric conversion element having a half-Heusler structure represented by the composition formula shown in Formula (2), those skilled in the art can understand, even without experimental data, that the maximum output is also improved for a thermoelectric conversion module using an n-type thermoelectric conversion element having a half-Heusler structure represented by any of the composition formulas shown in Formulas (3) to (7) above.

[0277] (Example 271) A thermoelectric conversion module of Example 271 was produced in the same manner as the thermoelectric conversion module of Example 38, except that the p-type thermoelectric conversion element was produced as follows.

[0278] [Fabrication of p-type thermoelectric conversion elements] A p-type thermoelectric conversion element with the composition formula Bi2Ca2Co2O9 was fabricated by the following method. First, bismuth oxide (Bi2O3), calcium carbonate (CaCO3), and cobalt oxide (Co3O4) were weighed and thoroughly mixed so that the molar ratio of Bi:Ca:Co was 2:2:2. The resulting mixture was placed in an alumina crucible and fired at 800°C in air for 10 hours. The fired product was then thoroughly mixed using an agate mortar and pestle. This powder was press-molded into a disk approximately 20 mm in diameter and 2 to 10 mm thick. A gold sheet was placed in an alumina boat, and the molded body was placed on top of the gold sheet and fired at 840°C in air for 20 hours. The resulting sintered body was then crushed using an agate mortar and pestle.

[0279] The resulting powder was pressed into a disk shape with a diameter of 40 mm and a thickness of 5 mm, and hot-press sintered under a uniaxial pressure of 10 MPa at 860°C in air for 20 hours. The resulting hot-pressed sintered compact was ground and cut so that the surface perpendicular to the pressed surface became a rectangular parallelepiped with a dimension of 3.5 mm x 3.5 mm and a length of 5 mm, yielding a p-type thermoelectric conversion material. The joining surface was the 3.5 mm x 3.5 mm surface cut from the surface perpendicular to the pressed surface.

[0280] [Fabrication of thermoelectric conversion module] As shown in Table 4-1, the thermoelectric conversion module of Example 271 was produced under the same conditions and by the same method as in Example 38, except that the material of the p-type thermoelectric conversion element was different.

[0281] Example 272 A thermoelectric conversion module of Example 272 was produced in the same manner as in Example 271, except that a silver paste containing an additive was used as shown in Table 4-1.

[0282] (Examples 273 to 293) The composition, firing conditions, and shape of the thermoelectric conversion material, the composition and shape of the conductive member, and the composition and amount of additives added to the silver paste were different as shown in Table 4-1 or Table 4-2, but the junction formation method and manufacturing conditions were the same as those in Example 272, and thermoelectric conversion modules in Examples 273 to 293 were produced.

[0283] For the thermoelectric conversion modules in Examples 271 to 293, the open circuit voltage, internal resistance, and maximum output were measured in accordance with Test Example 2 above.

[0284] The open circuit voltage, internal resistance and maximum output when the heating temperature of the thermoelectric conversion modules in Examples 271 to 293 was 500° C. are shown in Tables 4-1 and 4-2.

[0285] [Table 4-1]

[0286] [Table 4-2]

[0287] The thermoelectric conversion modules of Examples 271 to 293 are thermoelectric conversion modules equipped with n-type thermoelectric conversion elements having a half-Heusler structure represented by the composition formula of formula (2).

[0288] In the thermoelectric conversion modules of Examples 272 to 293, the silver paste for connecting the n-type thermoelectric conversion element and the conductive member contains a component (additive) consisting of at least one of titanium oxide and silver oxide, and the silver paste for connecting the p-type thermoelectric conversion element and the conductive member contains a component (additive) consisting of at least one of titanium oxide and silver oxide, or an oxide used in the p-type thermoelectric conversion element.

[0289] Furthermore, in the thermoelectric conversion modules of Examples 280 to 291, the silver paste for connecting the n-type thermoelectric conversion element and the conductive member is characterized by containing a component (additive) different from that of the silver paste for connecting the p-type thermoelectric conversion element and the conductive member.

[0290] Furthermore, in the thermoelectric conversion modules of Examples 271 to 279, 292, and 293, the silver paste for connecting the n-type thermoelectric conversion element and the conductive member is characterized by containing the same components (additives) as the silver paste for connecting the p-type thermoelectric conversion element and the conductive member.

[0291] The maximum output of the thermoelectric conversion module of Example 271, 84.9 mW, is greater than the maximum outputs of the thermoelectric conversion modules of Comparative Examples 2 to 9, 50.0 to 74.6 mW, shown in Table 2-15. Therefore, even when a thermoelectric oxide material having the composition formula of Bi2Ca2Co2O9 is applied to a p-type thermoelectric conversion element, it is possible to obtain a p-type thermoelectric conversion element having a half-Heusler structure (Ti 0.75 Hf 0.25 It was found that the maximum output of the thermoelectric conversion module can be improved by using NiSn.

[0292] As shown in Tables 4-1 and 4-2, the maximum outputs of the thermoelectric conversion modules of Examples 272 to 293, 102 to 141 mW, were greater than the maximum output of 84.9 mW of the thermoelectric conversion module of Example 271. This is because the use of silver paste containing additives (Ag2O, TiO2, Bi2Sr2Co2O9, or a combination thereof) reduced the electrical resistance at the junctions between the n-type and p-type thermoelectric conversion elements and the conductive member (silver sheet). Therefore, it was found that the maximum output of the thermoelectric conversion module of Example 271 could be improved by replacing the silver paste of the thermoelectric conversion module of Example 271 with silver paste containing additives (Ag2O, TiO2, Bi2Sr2Co2O9, or a combination thereof).

[0293] In Tables 4-1 and 4-2, both the n-type thermoelectric conversion element and the p-type thermoelectric conversion element are made of oxides, and the maximum output of the thermoelectric conversion module using silver paste without additives (Ag2O, TiO2, Bi2Sr2Co2O9 alone or a combination thereof) is not shown. However, since the Bi2Ca2Co2O9 (p-type thermoelectric conversion element) in Examples 271 to 293 has almost the same characteristics as the Bi2Sr2Co2O9 (p-type thermoelectric conversion element) in Examples 248 to 270, a comparison of the maximum output of the thermoelectric conversion module in Example 248 with the maximum output of the thermoelectric conversion module in Comparative Example 10 shows that the half-Heusler structure n-type thermoelectric conversion element (Ti 0.75 Hf 0.25 If it has been shown that the maximum output of a thermoelectric conversion module can be improved by using CaMn 0.98 Mo 0.02 It can be seen that the maximum output is greater than that of a thermoelectric conversion module using an n-type thermoelectric conversion element made of NiSn, a p-type thermoelectric conversion element made of Bi2Ca2Co2O9, and a silver paste without additives (Ag2O, TiO2, Bi2Sr2Co2O9 alone or a combination of these).

[0294] (Example 294) The thermoelectric conversion module in Example 294 was produced by the following method.

[0295] [Fabrication of n-type thermoelectric conversion elements] An n-type thermoelectric conversion element was produced in the same manner as in Example 38.

[0296] [Fabrication of p-type thermoelectric conversion elements] The composition formula is Ca 2.7 Bi 0.3A p-type thermoelectric conversion element represented by Co4O9 was fabricated by the following method. First, calcium carbonate (CaCO3), bismuth oxide (Bi2O3), and cobalt oxide (Co3O4) were weighed and thoroughly mixed so that the molar ratio of Ca:Bi:Co was 2.7:0.3:4. The resulting mixture was placed in an alumina crucible and fired at 800°C in air for 10 hours. The fired product was then thoroughly mixed using an agate mortar and pestle. This powder was press-molded into a disk approximately 20 mm in diameter and 2 to 10 mm thick. A gold sheet was placed in an alumina boat, and the molded body was placed on top of the gold sheet and fired at 860°C in air for 20 hours. The resulting sintered body was then pulverized using an agate mortar and pestle.

[0297] The resulting powder was pressed into a disk shape with a diameter of 40 mm and a thickness of 5 mm, and hot-press sintered under a uniaxial pressure of 10 MPa at 880°C in air for 20 hours. The resulting hot-pressed sintered compact was ground and cut into a rectangular parallelepiped with a surface perpendicular to the pressed surface measuring 3.5 mm x 3.5 mm and a length of 5 mm, yielding a p-type thermoelectric conversion material. The surface perpendicular to the pressed surface was the 3.5 mm x 3.5 mm joining surface.

[0298] [Preparation of silver paste] A silver paste was prepared using the same composition and method as the silver paste in Example 39.

[0299] [Fabrication of thermoelectric conversion module] A 3.2 mm × 7.5 mm, 0.1 mm thick silver sheet was used as the conductive member. Both junction surfaces of one p-type thermoelectric conversion element and both junction surfaces of one n-type thermoelectric conversion element were irradiated with ultraviolet light from a mercury lamp for 30 minutes.

[0300] The silver paste prepared by the above method was applied to the joining surface of the silver sheet. Here, the thickness of the silver paste before solidification was adjusted using screen printing so that the thickness after solidification would be 10 μm.

[0301] The bonding surface of the silver sheet coated with silver paste was placed on one of the bonding surfaces of the p-type thermoelectric element and the n-type thermoelectric element, and the silver sheet was pressed to bond it to one of the bonding surfaces of the p-type thermoelectric element and the n-type thermoelectric element, thereby connecting one of the bonding surfaces of the p-type thermoelectric element and one of the bonding surfaces of the n-type thermoelectric element. In this case, the distance between the p-type thermoelectric element and the n-type thermoelectric element was set to 0.5 mm.

[0302] The alumina insulating substrate described above was then placed on top of the silver sheet. Fifteen module precursors, each consisting of a pair of thermoelectric conversion elements, were fabricated and placed in a dryer at 100°C for approximately 30 minutes. The module precursors were then inverted and arranged in the positions of the elements in the thermoelectric conversion module. A 3.2 mm x 7 mm, 0.1 mm thick silver sheet, with silver paste applied to its joint surface as described above, was then placed on the joint surface to connect adjacent n-type and p-type thermoelectric conversion elements. This resulted in 15 pairs of n-type and p-type thermoelectric conversion elements connected alternately in series. A 3.2 mm x 30 mm, 0.1 mm thick silver sheet, with silver paste applied as described above, was placed on the joint surface between the n-type and p-type thermoelectric conversion elements at both ends of the 15 pairs of n-type and p-type thermoelectric conversion elements to serve as a power extraction member (extraction electrode).

[0303] Next, an insulating aluminum oxide (alumina: Al2O3) substrate measuring 35mm x 35mm and 0.8mm thick was placed on the silver sheet. This was then placed in a dryer again and heated at 100°C for approximately 30 minutes, after which it was placed in a hot press furnace where uniaxial pressure was applied to the bonding surface at 2.4MPa while the temperature was raised from room temperature to 200°C over one hour and then held at 200°C for one hour.

[0304] The pressure was then increased to 4.8 MPa, and the temperature was raised to 450°C over one hour. After holding at 450°C for one hour and a half, the temperature was raised to 800°C over two hours. One hour after the temperature began to rise, when the temperature reached 625°C, the pressure was increased to 9.6 MPa. While maintaining the pressure, the mixture was fired at 800°C for 30 minutes, after which the pressure was stopped and the mixture was allowed to cool naturally in the furnace, producing a thermoelectric conversion module with 15 pairs of n-type and p-type thermoelectric conversion elements. This heat treatment also bonded the silver sheet to the alumina substrate.

[0305] The thermoelectric conversion module in Example 294 has the same structure as the thermoelectric conversion module 300 shown in FIG.

[0306] (Example 295) The thermoelectric conversion module in Example 295 was fabricated by the following method, with the dimensions of the n-type thermoelectric conversion elements and p-type thermoelectric conversion elements, number of pairs, electrode members, dimensions of the electrode members, application of silver paste, and heat treatment conditions for junction formation being the same as in Example 294, except that the additives added to the silver paste were different.

[0307] [Preparation of silver paste] A silver paste was prepared using a commercially available silver paste (product name: MH-108A, silver content: 85 wt%) manufactured by Tanaka Kikinzoku Co., Ltd. This silver paste consisted of 75 wt% silver powder (particle size: 0.1-5 μm), 1 wt% borosilicate bismuth glass, 5 wt% ethyl cellulose, 4 wt% terpineol, and 5 wt% butyl carbitol acetate. The wet silver paste was taken as 100 wt%. Silver oxide (AgO) powder was then sieved using a 38 μm mesh sieve (JIS standard 390 mesh). 8 wt% of the sieved silver oxide (AgO) powder was added and thoroughly kneaded to obtain a silver paste. This silver paste was used as the silver paste for bonding n-type thermoelectric elements.

[0308] In addition, a commercially available silver paste (product name: MH-108A, silver content: 85 wt%) manufactured by Tanaka Kikinzoku Co., Ltd. was used in a wet state as 100 wt %. The oxide powder (Ca 2.7 Bi0.3 Ca 2.7 Co4O9) was classified and sieved to obtain oxide powder (Ca 2.7 Bi 0.3 Ca 2.7 Co4O9) was added at 6 wt % and thoroughly mixed to obtain a silver paste, which was used as the silver paste for bonding p-type thermoelectric conversion elements.

[0309] [Test Example 3] For the thermoelectric conversion module of Example 294, the aluminum oxide substrate surface was heated in air at 100 to 500°C using a plate-type electric furnace, and the opposite end was cooled with a copper jacket through which 20°C water was circulated to create a temperature difference.

[0310] The extraction electrodes (silver sheets) placed on the high-temperature sides of the p-type thermoelectric conversion element and n-type thermoelectric conversion element, which are at both ends of the thermoelectric conversion module, were connected to an electrical load device, and the current and voltage were measured while changing the external load resistance, thereby obtaining the internal resistance and output of the thermoelectric conversion module.

[0311] In this measurement, the current-voltage characteristic is obtained as a straight line, and the absolute value of the slope of the line (consisting of negative values) is the internal resistance of the thermoelectric conversion module.

[0312] The output is the product of the current and the voltage, and is a quadratic function of the current. The measured values ​​were regressed on the quadratic function, and the maximum value of the quadratic curve obtained from the function was taken as the maximum output. The thermoelectric conversion module exhibits maximum output when the external load resistance matches the internal resistance, and when calculated using a regression curve, the maximum output was also obtained at the point where they matched.

[0313] Fig. 12 is a diagram showing the relationship between the maximum output and the heating temperature in the thermoelectric conversion module of Example 294. In Fig. 12, the vertical axis represents the maximum output, and the horizontal axis represents the heating temperature.

[0314] Referring to Figure 12, the maximum output of the thermoelectric conversion module of Example 294 is approximately 15 times the maximum output of the thermoelectric conversion module of Example 39 in the temperature range of 100°C to 500°C, and even in a thermoelectric conversion module having multiple pairs of p-type thermoelectric conversion elements and n-type thermoelectric conversion elements, good joint characteristics (electrical resistance of the joint) can be obtained between the p-type thermoelectric conversion elements and n-type thermoelectric conversion elements and the conductive member.

[0315] In addition, while maintaining the heating temperature at 500°C, the external load resistance was adjusted so that a current of 1 A was output from the thermoelectric conversion module, and continuous power generation was performed in air for approximately 1,000 hours.

[0316] Fig. 13 is a diagram showing the relationship between power generation output and power generation time in the thermoelectric conversion modules of Examples 294 and 295. In Fig. 13, the vertical axis represents the ratio of power generation output (t) at time t to the power generation output at the start of power generation (0 hours) (power generation output (t) / power generation output (0 hours)), and the horizontal axis represents power generation time t. Fig. 13(b) shows the relationship between power generation output and power generation time, with the vertical axis of Fig. 13(a) enlarged.

[0317] 13, the ratio (power generation output (t) / power generation output (0 hours)) decreased by approximately 0.7% after 1000 hours in Example 294, but only decreased by 0.2% in Example 295. No significant deterioration was observed in either Example 294 or 295, but it was found that it is more preferable to use a silver paste with silver oxide added as the silver paste for n-type thermoelectric conversion elements and a silver paste with oxide powder added as the silver paste for p-type thermoelectric conversion elements.

[0318] Therefore, the thermoelectric conversion module according to the embodiment of the present invention has excellent durability at high temperatures in air, and has higher power generation efficiency than oxide thermoelectric modules, which have been proven to have high durability.

[0319] These results indicate that a thermoelectric conversion module using a silver paste containing specific amounts of additives (Ag2O, TiO2, thermoelectric conversion materials for p-type thermoelectric conversion elements) and an n-type thermoelectric conversion element with a half-Heusler structure has durability equivalent to that of an oxide thermoelectric conversion module, which has high durability, at high temperatures and in air, and also has superior power generation performance to that of an oxide thermoelectric conversion module. Therefore, the thermoelectric conversion module according to the embodiment of the present invention can effectively utilize high-temperature exhaust heat from factories, automobiles, and waste incineration plants.

[0320] In Examples 271 to 295 described above, it was shown that the maximum output was improved for a thermoelectric conversion module using an n-type thermoelectric conversion element having a half-Heusler structure represented by the composition formula shown in Formula (2) above. However, similar improvements in maximum output can also be achieved in a thermoelectric conversion module using an n-type thermoelectric conversion element having a half-Heusler structure represented by any of the composition formulas shown in Formulas (3) to (7) above. This is because, as shown in Tables 1-1 to 1-3, the n-type thermoelectric conversion elements of Examples 1 to 37 have a larger ZT than the n-type thermoelectric conversion element of Comparative Example 1. Therefore, if experimental data are shown to demonstrate that the maximum output is improved for a thermoelectric conversion module using an n-type thermoelectric conversion element having a half-Heusler structure represented by the composition formula shown in Formula (2), those skilled in the art can understand, even without experimental data, that the maximum output is also improved in a thermoelectric conversion module using an n-type thermoelectric conversion element having a half-Heusler structure represented by any of the composition formulas shown in Formulas (3) to (7) above.

[0321] Furthermore, since n-type thermoelectric conversion elements having a half-Heusler structure represented by the composition formulas of formulas (2) to (7) are generally represented by the composition formula of formula (1), those skilled in the art will understand that the maximum output of a thermoelectric conversion module including n-type thermoelectric conversion elements having a half-Heusler structure represented by the composition formula of formula (1) will be improved.

[0322] The content of additives added to the silver paste will be explained below. Hereinafter, the silver paste used to bond n-type thermoelectric conversion elements and conductive members will be referred to as "n-type silver paste," and the silver paste used to bond p-type thermoelectric conversion elements and conductive members will be referred to as "p-type silver paste."

[0323] Fig. 14 is a diagram showing the relationship between the maximum output and the AgO content added to the p-type silver paste and n-type silver paste in the thermoelectric conversion modules of Examples 38 to 41, 47, and 48. In Fig. 14, the vertical axis represents the maximum output of the thermoelectric conversion module, and the horizontal axis represents the AgO content in the p-type silver paste and n-type silver paste. Note that p-type silver paste refers to the silver paste that bonds the p-type thermoelectric conversion element and the conductive member, and n-type silver paste refers to the silver paste that bonds the n-type thermoelectric conversion element and the conductive member (the same applies hereinafter).

[0324] Referring to FIG. 14, the maximum output power is maintained at 126 mW or more when the AgO content is in the range of 0.5 wt % to 10 wt %. On the other hand, when the AgO content is 0.0 wt %, the maximum output power is 99 mW. Therefore, the maximum output power of the thermoelectric conversion module can be improved by using p-type silver paste and n-type silver paste containing 0.5 wt % to 10 wt % AgO. Therefore, when AgO is added to the p-type silver paste and n-type silver paste, the AgO content is preferably 0.5 wt % to 10 wt %.

[0325] Fig. 15 is a diagram showing the relationship between the maximum output and the TiO content added to the p-type silver paste and n-type silver paste in the thermoelectric conversion modules of Examples 38, 49 to 51, 57, and 58. In Fig. 15, the vertical axis represents the maximum output of the thermoelectric conversion module, and the horizontal axis represents the TiO content in the p-type silver paste and n-type silver paste.

[0326] Referring to Figure 15, the maximum output is maintained at 114 mW or more when the TiO2 content is in the range of 0.5 to 10 weight percent. On the other hand, when the TiO2 content is 0.0 weight percent, the maximum output is 99 mW. Therefore, the maximum output of the thermoelectric conversion module can be improved by using p-type silver paste and n-type silver paste to which 0.5 to 10 weight percent TiO2 is added. Therefore, when TiO2 is added to the p-type silver paste and n-type silver paste, the TiO2 content is preferably 0.5 to 10 weight percent.

[0327] Figure 16 shows the relationship between the maximum output power of the thermoelectric conversion modules of Examples 38, 62, 63, and 69 and the TiO content added to the p-type silver paste. In Figure 16, the vertical axis represents the maximum output power of the thermoelectric conversion modules, and the horizontal axis represents the TiO content in the p-type silver paste. 3 wt% AgO was added to the n-type silver paste.

[0328] Referring to FIG. 16, the maximum output power is maintained at 128 mW or more when the TiO content is in the range of 1.0 wt % to 6.0 wt %. On the other hand, when the TiO content is 0.0 wt %, the maximum output power is 99 mW. Therefore, the maximum output power of the thermoelectric conversion module can be improved by maintaining the AgO content of the n-type silver paste at 3.0 wt % and using a p-type silver paste to which TiO is added at 1.0 wt % to 6.0 wt %. Therefore, when the AgO content of the n-type silver paste is maintained at 3.0 wt % and TiO is added to the p-type silver paste, the TiO content is preferably 1.0 wt % to 6.0 wt %.

[0329] When the TiO2 content is 1.0 wt% to 6.0 wt%, the maximum output of the thermoelectric conversion module is 128 mW to 137 mW. As a result, the increase in maximum output due to the addition of 1.0 wt% TiO2 is 128 / 99 = 1.29 times, and the increase in maximum output due to the addition of 1.0 wt% TiO2 is 137 / 128 = 1.07 times. Therefore, the increase in maximum output when the TiO2 content is 1.0 wt% to 6.0 wt% is smaller and more nearly constant than when the TiO2 content is 1.0 wt% or less. Therefore, a TiO2 content of 1.0 wt% is critical for maintaining the maximum output of the thermoelectric conversion module at a constant value above 128 mW.

[0330] FIG. 17 shows the relationship between the maximum output and the amount of Ca added to the p-type silver paste in the thermoelectric conversion modules of Examples 38, 72 to 75 and the thermoelectric conversion modules of Examples 38, 86 to 89. 2.7 Bi 0.3 17 is a graph showing the relationship between the content of Ca and CoO in the p-type silver paste. 2.7 Bi 0.3 In Figure 17, the maximum output and Ca content are shown in the lower part. 2.7 Bi 0.3 The relationship between the content of Co4O9 and the maximum output of the thermoelectric conversion modules of Examples 38 and 72 to 75 was 2.7 Bi 0.3 The relationship between the Co4O9 content and the maximum output in the upper row is shown. 2.7 Bi 0.3 The relationship between the content of Co4O9 and the maximum output of the thermoelectric conversion modules of Examples 38, 86 to 89 and the amount of Ca added to the p-type silver paste was 2.7 Bi 0.3 The relationship between the content of Co4O9 and the Ca 2.7 Bi 0.3 Co4O9 is an oxide used in p-type thermoelectric conversion elements.

[0331] Referring to FIG. 17, the maximum outputs of the thermoelectric conversion modules of Examples 38 and 72 to 75 were 2.7 Bi 0.3 When the content of Co4O9 is in the range of 0.5 [wt%] to 6.0 [wt%], it maintains 133 [mW] or more. 2.7 Bi 0.3 When the content of Co4O9 is 0.0 [wt%], the maximum output is 99 [mW]. Therefore, the content of Ag2O added to the n-type silver paste is kept at 3.0 [wt%], and 0.5 [wt%] to 6.0 [wt%] of Ca is added. 2.7 Bi 0.3 By using p-type silver paste with Co4O9 added, the maximum output of the thermoelectric conversion module can be improved. Therefore, by keeping the content of Ag2O added to the n-type silver paste at 3.0 [wt%], Ca is added to the p-type silver paste. 2.7 Bi 0.3 When Co4O9 is added, Ca 2.7 Bi 0.3 The content of Co4O9 is preferably 0.5 [wt %] to 6.0 [wt %] (see the lower part of FIG. 17).

[0332] In addition, the maximum output of the thermoelectric conversion modules of Examples 38, 86 to 89 was 2.7 Bi 0.3 When the content of Co4O9 is in the range of 0.5 to 6.0 weight percent, it maintains 128 mW or more. 2.7 Bi 0.3 When the content of Co4O9 is 0.0 [wt%], the maximum output is 99 [mW]. Therefore, the content of TiO2 added to the n-type silver paste is kept at 3.0 [wt%], and 0.5 [wt%] to 6.0 [wt%] of Ca is added. 2.7 Bi 0.3 By using p-type silver paste with Co4O9 added, the maximum output of the thermoelectric conversion module can be improved. Therefore, the content of TiO2 added to the n-type silver paste is kept at 3.0 [wt%], and Ca is added to the p-type silver paste. 2.7 Bi 0.3 When Co4O9 is added, Ca 2.7 Bi 0.3The content of Co4O9 is preferably 0.5 [wt %] to 6 [wt %] (see the upper part of FIG. 17).

[0333] Fig. 18 is a diagram showing the relationship between the maximum output and the content of Ag2O added to the n-type silver paste in the thermoelectric conversion modules of Examples 38, 81 to 85. In Fig. 18, the vertical axis represents the maximum output of the thermoelectric conversion module, and the horizontal axis represents the content of Ag2O in the n-type silver paste. Note that the p-type silver paste contained 6 [wt %] of Ca. 2.7 Bi 0.3 Co4O9 was added.

[0334] Referring to FIG. 18, the maximum output is maintained at 119 mW or more when the Ag2O content is in the range of 0.5 wt % to 10 wt %. On the other hand, when the Ag2O content is 0.0 wt %, the maximum output is 99 mW. Therefore, the amount of Ca added to the p-type silver paste 2.7 Bi 0.3 The maximum output of the thermoelectric conversion module can be improved by using an n-type silver paste containing 0.5 to 10 weight percent of Ag2O while maintaining the Co4O9 content at 6.0 weight percent. 2.7 Bi 0.3 When the content of Co4O9 is kept at 6.0 [wt %] and Ag2O is added to the n-type silver paste, the content of Ag2O is preferably 0.5 [wt %] to 10 [wt %].

[0335] Fig. 19 is a diagram showing the relationship between the maximum output and the TiO2 content added to the n-type silver paste in the thermoelectric conversion modules of Examples 38, 90, 95 to 98 and Examples 271, 288 to 291. In Fig. 19, the vertical axis represents the maximum output of the thermoelectric conversion module, and the horizontal axis represents the TiO2 content in the n-type silver paste. The lower part of Fig. 19 shows the relationship between the maximum output of the thermoelectric conversion module and the TiO2 content in the n-type silver paste when 6 [wt %] of Ca was added to the p-type silver paste. 2.7 Bi 0.3The figure shows the relationship between the maximum output and the TiO content added to the n-type silver paste in the thermoelectric conversion modules of Examples 38, 90, and 95 to 98 when Co4O9 was added, and the upper part of Figure 19 shows the relationship between the maximum output and the TiO content added to the n-type silver paste in the thermoelectric conversion modules of Examples 271, 288 to 291 when 6 [wt %] Bi2Ca2Co4O9 was added to the p-type silver paste.

[0336] 19, the maximum output of the thermoelectric conversion modules of Examples 38, 90, 95 to 98 is maintained at 123 [mW] or more when the TiO2 content is in the range of 0.5 [wt %] to 10 [wt %]. On the other hand, when the TiO2 content is 0.0 [wt %], the maximum output is 99 [mW]. Therefore, the amount of Ca added to the p-type silver paste 2.7 Bi 0.3 By maintaining the Co4O9 content at 6.0 [wt%] and using n-type silver paste with 0.5 [wt%] to 10 [wt%] of TiO2 added, the maximum output of the thermoelectric conversion module can be improved. 2.7 Bi 0.3 When TiO2 is added to the n-type silver paste while the Co4O9 content is kept at 6.0 [wt %], the TiO2 content is preferably 0.5 [wt %] to 10 [wt %] (see the lower part of FIG. 19).

[0337] Furthermore, the maximum output of the thermoelectric conversion modules of Examples 271, 288 to 291 is maintained at 114 [mW] or more when the TiO2 content is in the range of 0.5 [wt %] to 5.0 [wt %]. On the other hand, when the TiO2 content is 0.0 [wt %], the maximum output is 84.9 [mW]. Therefore, the Bi added to the p-type silver paste 02 By maintaining the Ca2Co4O9 content at 6.0 [wt%] and using n-type silver paste with 0.5 [wt%] to 5.0 [wt%] TiO2 added, the maximum output of the thermoelectric conversion module can be improved. 02When TiO2 is added to the n-type silver paste while the Ca2Co4O9 content is kept at 6.0 [wt %], the TiO2 content is preferably 0.5 [wt %] to 5.0 [wt %] (see the upper part of FIG. 19).

[0338] Fig. 20 shows the relationship between the maximum output of the thermoelectric conversion modules of Examples 248, 265 to 268 and the TiO content added to the n-type silver paste. In Fig. 20, the vertical axis represents the maximum output of the thermoelectric conversion module, and the horizontal axis represents the TiO content in the n-type silver paste. Note that 6.0 wt% of BiSrCoO was added to the p-type silver paste.

[0339] Referring to FIG. 20, the maximum output is maintained at 114 mW or more when the TiO2 content is in the range of 0.5 wt % to 5.0 wt %. On the other hand, when the TiO2 content is 0.0 wt %, the maximum output is 88 mW. Therefore, the amount of Bi added to the p-type silver paste 02 By maintaining the Ca2Co4O9 content at 6.0 [wt%] and using n-type silver paste with 0.5 [wt%] to 5.0 [wt%] TiO2 added, the maximum output of the thermoelectric conversion module can be improved. 02 When TiO2 is added to the n-type silver paste while the Ca2Co4O9 content is kept at 6.0 [wt %], the TiO2 content is preferably 0.5 [wt %] to 5.0 [wt %].

[0340] 20, the rate of increase in the maximum output of the thermoelectric conversion module when the TiO2 content is 0.5 to 5.0 weight percent is smaller than the rate of increase in the maximum output of the thermoelectric conversion module when the TiO2 content is 0.5 weight percent or less, and is substantially constant. Therefore, a TiO2 content of 0.5 weight percent is critical for maintaining the maximum output of the thermoelectric conversion module substantially constant at 100 mW or more.

[0341] As shown in Figures 14 and 15, when the content of the additive (Ag2O or TiO2) added to the n-type silver paste and the p-type silver paste is changed simultaneously, the maximum output of the thermoelectric conversion module can be improved by setting the content of the additive (Ag2O or TiO2) within the above-mentioned range compared to when no additive is added to the silver paste.

[0342] Furthermore, as shown in Figures 16 to 20, by keeping the content of the additive added to either the n-type silver paste or the p-type silver paste constant and setting the content of the additive added to the other silver paste within the above-mentioned range, the maximum output of the thermoelectric conversion module can be improved compared to when no additive is added to the silver paste.

[0343] Therefore, Ag2O, TiO2 and Ca 2。7 Bi 0.3 The maximum output of the thermoelectric conversion module can be improved by adding either Co4O9 to the silver paste.

[0344] The resistivity of the silver paste used in the above-mentioned examples will now be described. The resistivity of the silver paste was measured by the following method. (1) Silver paste is applied to an alumina (Al2O3) substrate by screen printing. (2) Firing the silver paste at 860°C for 2 hours (3) Measure the resistivity of the silver paste using the four-probe method

[0345] In measuring resistivity using the four-probe method, four gold-plated probes with a diameter of 1 mm were prepared and arranged in a line on the silver paste at intervals of 2 mm. A constant current was applied using the two outer probes while changing the current value (including changing the polarity of the current), and the voltage between the two inner probes was measured. The slope of the relationship between current and voltage was measured as the resistivity of the silver paste.

[0346] Silver paste without additives (product name: MH-108A silver paste), silver paste with Ag2O added (product name: MH-108A silver paste with Ag2O added), silver paste with TiO2 added (product name: MH-108A silver paste with TiO2 added), Ca 2.7 Bi 0.3 Silver paste containing Co4O9 (product name: MH-108A silver paste containing Ca 2.7 Bi 0.3 The resistivity of the silver paste (silver paste with Co4O9 added) and the silver paste (silver paste with Ag2O and TiO2 added) was measured using the above measurement method. The results are shown in Table 5.

[0347] [Table 5]

[0348] The resistivity of the silver paste shown in Table 5 is 2.7 Bi 0.3 For each Co4O9 additive, the resistivity is the average of four samples prepared at 0, 0.5, and 10 wt% contents. For the TiO2 additive, the resistivity is the average of four samples prepared at 0, 0.5, and 8 wt% contents. For the Ag2O and TiO2 additives, the resistivity is the average of four samples prepared at (Ag2O, TiO2) = (0.5 wt%, 0.5 wt%), (1.5 wt%, 1.5 wt%), and (2.0 wt%, 1.0 wt%) contents. The thickness and width of the silver paste for each sample are shown in Table 5.

[0349] As shown in FIGS. 19 and 20, the preferred Ag2O content is 0.2 [wt %] to 10 [wt %], the preferred TiO2 content is 0.14 [wt %] to 10 [wt %], and as shown in FIG. 17, the preferred Ca 2.7 Bi 0.3The content of Co4O9 is 0.12 [wt%] to 6 [wt%], so in Table 5, when one additive is added, Ag2O and Ca 2.7 Bi 0.3 The amounts of Co4O9 added were 0.5 wt% and 10 wt%, and the amounts of TiO2 added were 0.5 wt% and 8 wt%. When two additives were added, the amounts of Ag2O and TiO2 added were (Ag2O, TiO2) = (0.5 wt%, 0.5 wt%), (1.5 wt%, 1.5 wt%), and (2.0 wt%, 1.0 wt%).

[0350] According to Table 5, the silver paste used in the examples has a resistivity in the range of 2.60 μΩcm to 13.0 μΩcm. The resistivity of the silver paste is reduced by adding Ag2O, but not by adding TiO2 or Ca. 2.7 Bi 0.3 The resistance increases with the addition of Co4O9, and decreases or increases with the addition of Ag2O and TiO2 depending on the Ag2O and TiO2 contents. However, according to the above-mentioned examples, it was found that the maximum output of the thermoelectric conversion module can be improved by using a silver paste with a resistivity in the range of 2.60 μΩcm to 13.0 μΩcm. Therefore, the silver paste used in the thermoelectric conversion module only needs to have a resistivity in the range of 2.60 μΩcm to 13.0 μΩcm. In the above-described examples, the silver paste placed between the n-type thermoelectric conversion element and the conductive member is the "first silver paste," and the silver paste placed between the p-type thermoelectric conversion element and the conductive member is the "second silver paste." [Explanation of symbols]

[0351] 1,12,290,430 Insulating substrate 2, 3, 11, 102~116, 271~286, 301~315, 412~425 Conductive materials 4,5,8,9,191~222,231~262,351~310 Connection layer 6,123,124,127,128,131,132,135,136,139,140,143,144,147,148,151,152,155,156,159,160,163,164,167,168,171,172,175,176,179,180,183,184,322,324,326,328,330,332,334,336,338,340,342,344,346,348,350 n-type thermoelectric conversion elements 7,121,122,125,126,129,130,133,134,137,138,141,142,145,146,149,150,153,154,157,158,161,162,165,166,169,170,173,174,177,178,181,182,321,323,325,327,329,331,333,335,337,339,341,343,345,347,349 p-type thermoelectric conversion element 10,100,300 Thermoelectric conversion module 101,117,411,426 Extraction electrode.

Claims

1. an n-type thermoelectric conversion element having a half-Heusler structure with a negative Seebeck coefficient; a p-type thermoelectric conversion element including an oxide having a positive Seebeck coefficient at a temperature of 25°C or higher; a conductive member that electrically connects one end of the n-type thermoelectric conversion element and one end of the p-type thermoelectric conversion element; a connection layer including a conductive metal made of silver and located between the n-type thermoelectric conversion element and the conductive member; a connection layer including a conductive metal made of silver and located between the p-type thermoelectric conversion element and the conductive member; A thermoelectric conversion module comprising: The n-type thermoelectric conversion element is represented by any one of the following formulas (2) to (7): Ti 1-a Hf a NiSn... (2) [In formula (2), 0.0≦a≦0.5.] Ti 1-b Zr b NiSn...(3) [In formula (3), 0.0≦b≦0.5.] Zr 1-c Hf c NiSn...(4) [In formula (4), 0.0≦c≦0.5.] Zr 1-d Ti d NiSn... (5) [In formula (5), 0.0≦d≦0.5.] Zr 1-ef Ti e Hf f NiSn...(6) [In formula (6), 0.0≦e≦0.25 and 0.0≦f≦0.25.] Ti 1-gh Zr g Hf h NiSn...(7) [In formula (7), 0.0≦g≦0.25 and 0.0≦h≦0.25.] the n-type thermoelectric conversion element is made of an alloy having a half-Heusler structure with a negative Seebeck coefficient, and has a negative Seebeck coefficient in a temperature range of 25°C to 500°C; The p-type thermoelectric conversion element is made of an oxide represented by the following formula (8) or formula (9) and has a positive Seebeck coefficient at a temperature of 25°C or higher: Ca 3-j Bi j Co 4 O 9 ・・・(8) [In formula (8), 0.0≦j≦0.5.] Bi 2.0+k M 2.0+m Co 2 O 9 ・・・(9) [In formula (9), M is at least one element selected from Ca and Sr, and −0.2≦k≦0.2 and −0.2≦m≦0.2.] the conductive member is connected to the n-type thermoelectric conversion element via the connection layer between the n-type thermoelectric conversion element and the conductive member, and is connected to the p-type thermoelectric conversion element via the connection layer between the p-type thermoelectric conversion element and the conductive member; the connection layer between the n-type thermoelectric conversion element and the conductive member further includes an oxide to reduce junction resistance between the n-type thermoelectric conversion element and the connection layer between the n-type thermoelectric conversion element and the conductive member; the connection layer between the p-type thermoelectric conversion element and the conductive member further includes an oxide to reduce junction resistance between the p-type thermoelectric conversion element and the connection layer between the p-type thermoelectric conversion element and the conductive member; A thermoelectric conversion module, wherein the oxide of the connection layer to the p-type thermoelectric conversion element is at least one of titanium oxide and silver oxide.

2. 2. The thermoelectric conversion module according to claim 1, wherein the oxide of the connection layer to the n-type thermoelectric conversion element is at least one of titanium oxide and silver oxide.

3. 3. The thermoelectric conversion module according to claim 1, wherein the connection layer includes a sintered body of silver powder.

4. 4. The thermoelectric conversion module according to claim 1, wherein the connection layer contains the oxide so as to have a resistivity of 2.60 μΩcm to 13.0 μΩcm as measured by a four-point probe method.

5. A thermoelectric conversion module described in any one of claims 1 to 4, characterized in that the area of ​​the surface of the p-type thermoelectric conversion element parallel to the contact surface with the conductive member is larger than the area of ​​the surface of the n-type thermoelectric conversion element parallel to the contact surface with the conductive member.

6. 6. The thermoelectric conversion module according to claim 1, wherein the conductive member is made of a metal substrate or a conductive ceramic substrate.

7. 7. The thermoelectric conversion module according to claim 6, wherein the metal substrate is made of any one of gold, silver, and platinum.

8. 8. The thermoelectric conversion module according to claim 1, wherein the oxide of the connection layer to the p-type thermoelectric conversion element is silver oxide.

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