Thermoelectric materials, thermoelectric elements, and thermoelectric modules

Abstract

To provide a thermoelectric conversion material capable of improving the efficiency of thermoelectric conversion.SOLUTION: A thermoelectric conversion material includes a base material composed of SiGe, a first additive element functioning as a dopant, a second additive element different from the first additive element, and oxygen. The second additive element includes at least one of Mg, Ca, and Ti. A content ratio of the second additive element relative to the base material is 0.5 at% or more and 5 at% or less. In a field of view selected such that a grain boundary crosses opposite sides of the field of view to each other that is the field of view of a cross-section of the base material, distributions of the second additive element and oxygen have a positive correlation. A correlation coefficient of the correlation is in a range of 0.2 or more and less than 1.0.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] This disclosure relates to thermoelectric materials, thermoelectric elements, and thermoelectric modules. [Background technology]

[0002] SiGe-based thermoelectric conversion materials that convert temperature differences (thermal energy) into electricity have been disclosed (see, for example, Patent Documents 1, 2, 3, and Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2000-114606 [Patent Document 2] Special Publication No. 2011-527517 [Patent Document 3] Japanese Patent Publication No. 2013-157362 [Non-patent literature]

[0004] [Non-Patent Document 1] Tatsuhiko Aizawa et al., “Solid-State Synthesis of Thermoelectric Materials in Mg-Si-Ge System”, Material Transactions, Vol. 46, No. 7 (2005) pp. 1490 to 1496 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The efficiency of converting a temperature difference (thermal energy) into electrical energy using materials for thermoelectric conversion (thermoelectric conversion materials) is given by the following equation (1).

[0006] η = ΔT / T h·(M - 1) / (M + T c / T h )···(1)

[0007] η is the conversion efficiency, ΔT is the difference between T h and T c and, T h is the temperature on the high - temperature side, T c is the temperature on the low - temperature side, M is (1 + ZT) 1 / 2 , ZT = α 2 ST / κ, ZT is the dimensionless performance index, α is the Seebeck coefficient, S is the conductivity, and κ is the thermal conductivity. The conversion efficiency is a monotonic increasing function of ZT.

[0008] Also, the power factor (hereinafter sometimes abbreviated as "PF") corresponding to the power generation amount per unit temperature difference is shown by the following formula (2). Here, in formula (2), α is the Seebeck coefficient and S is the conductivity.

[0009] PF = α 2 ×S···(2)

[0010] In order to perform efficient thermoelectric conversion, it is important to increase PF. If PF can be increased, the efficiency of thermoelectric conversion can be improved.

[0011] Therefore, one of the objectives is to provide a thermoelectric conversion material that can improve the efficiency of thermoelectric conversion.

Means for Solving the Problems

[0012] The thermoelectric conversion material according to the present disclosure includes a base material composed of SiGe, a first additive element that functions as a dopant, a second additive element different from the first additive element, and oxygen. The second additive element includes at least one of Mg, Ca, and Ti. The content ratio of the second additive element with respect to the base material is 0.5 at% or more and 5 at% or less. In a view of the cross-section of the base material, in a view selected so that grain boundaries cross opposite sides of the view, the distributions of the second additive element and oxygen have a positive correlation. The correlation coefficient of the correlation is in the range of 0.2 or more and less than 1.0.

Advantages of the Invention

[0013] According to the above thermoelectric conversion material, the efficiency of thermoelectric conversion can be improved.

Brief Description of the Drawings

[0014] [Figure 1] FIG. 1 is a schematic diagram showing the state of the structure of the thermoelectric conversion material in Embodiment 1. [Figure 2] FIG. 2 is a TEM image showing a part of the obtained thermoelectric conversion material, which is a cross-section of the base material. [Figure 3] FIG. 3 is a diagram showing the distribution analysis result of O (oxygen) in TEM / EDX. [Figure 4] FIG. 4 is a diagram showing the distribution analysis result of Mg (magnesium) in TEM / EDX. [Figure 5] FIG. 5 is a TEM image showing a part of a thermoelectric conversion material that does not contain a second additive element, which is outside the scope of the present disclosure. [Figure 6] FIG. 6 is a diagram showing the distribution analysis result of O (oxygen) in TEM / EDX of a thermoelectric conversion material outside the scope of the present disclosure. [Figure 7] FIG. 7 is a graph showing the relationship between the content ratio and PF when the type of the second additive element and the content ratio of the second additive element are variously changed. [Figure 8] FIG. 8 is a graph showing the correlation coefficient in each region. [Figure 9]Figure 9 is a graph showing the relationship between oxygen concentration and magnesium concentration. [Figure 10] Figure 10 is a schematic diagram showing the structure of a π-type thermoelectric element (power generation element), which is a thermoelectric conversion element in this embodiment. [Figure 11] Figure 11 shows an example of the structure of a power generation module. [Modes for carrying out the invention]

[0015] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described. The thermoelectric conversion material according to this disclosure is (1) The material comprises a base material composed of SiGe, a first dopant element functioning as a dopant, a second dopant element different from the first dopant element, and oxygen (O). The second dopant element includes at least one of Mg (magnesium), Ca (calcium), and Ti (titanium). The content of the second dopant element relative to the base material is 0.5 at% or more and 5 at% or less. In a cross-sectional view of the base material, selected such that the grain boundaries intersect opposite sides of the view, the distribution of the second dopant element and oxygen has a positive correlation. The correlation coefficient is in the range of 0.2 or more and less than 1.0.

[0016] The inventors of this application considered using SiGe, which is suitable for use in thermoelectric conversion materials, as a base material and aiming to improve the efficiency of thermoelectric conversion by increasing the PF (Peristaltic Frequency). They believed that suppressing the decrease in conductivity was necessary to increase PF, and thus arrived at the construction of the thermoelectric conversion material according to this disclosure. Here, the inventors focused on the fact that Si in the base material oxidizes during the manufacturing process, resulting in a decrease in conductivity. Even if measures such as working in an inert gas atmosphere during the manufacturing process are taken, a certain amount of oxygen inevitably remains in the thermoelectric conversion material. The inventors then diligently investigated and attempted to suppress the decrease in conductivity of the thermoelectric conversion material and consequently increase PF by incorporating an element that adsorbs oxygen into the thermoelectric conversion material, thereby suppressing the oxidation of Si. Specifically, they attempted to suppress the decrease in conductivity by adding a second additive element that captures oxygen in addition to a first additive element that functions as a dopant, thereby creating a low-oxygen concentration region in the thermoelectric conversion material. In this case, the aggregation of a second additive element and oxygen at the grain boundaries generates an energy filtering effect, increasing the Seebeck coefficient and thus increasing the PF.

[0017] The thermoelectric conversion material of this disclosure contains a second additive element, unlike the first additive element, which includes at least one of Mg, Ca, and Ti. Such a second additive element is more easily oxidized than Si. Therefore, in the thermoelectric conversion material, the oxidation of the second additive element can be prioritized over the oxidation of Si. Furthermore, the content ratio of the second additive element to the base material is between 0.5 at% and 5 at%. By setting the content ratio of the second additive element to 0.5 at% or more, it is possible to sufficiently suppress the decrease in conductivity by prioritizing the oxidation of the second additive element over the oxidation of Si. Furthermore, by setting the content ratio of the second additive element to 5 at% or less, it is possible to suppress the significant deposition of oxides at the interface of the second additive element due to the addition of an excess amount of the second additive element, thereby suppressing the decrease in conductivity due to carrier scattering. Furthermore, in a field of view of the cross-section of the base material, selected such that grain boundaries intersect opposite edges of the field of view, the distribution of the second additive element and oxygen exhibits a positive correlation, and the correlation coefficient is in the range of 0.2 to less than 1.0. By doing so, the widespread distribution of uniform oxygen concentration in the distribution of the second additive element and oxygen is suppressed, and high-oxygen concentration regions and low-oxygen concentration regions appearing due to the inclusion of grain boundaries can be distributed. As a result, since conductivity is high in the low-oxygen concentration regions, the overall low-oxygen concentration region can be distributed to improve conductivity. Therefore, such a thermoelectric conversion material can improve the efficiency of thermoelectric conversion.

[0018] (2) In (1) above, the field of view of 100 nm square to 2 μm square may include a first region where the oxygen concentration is a first concentration and a second region where the oxygen concentration is a second concentration higher than the first concentration. The difference between the first concentration and the second concentration may be 10 at% or more. By doing so, the high oxygen concentration region and the low oxygen concentration region can be clearly defined, ensuring high conductivity in the low oxygen concentration region and increasing PF to improve the efficiency of thermoelectric conversion.

[0019] (3) In (1) or (2) above, the thermoelectric conversion material may contain nitrogen (N). By doing so, the energy filtering effect can be greatly increased, and thus the efficiency of thermoelectric conversion can be further improved.

[0020] (4) In any of (1) to (3) above, the base material may include an amorphous phase. By doing so, the efficiency of thermoelectric conversion can be further improved.

[0021] (5) In any of (1) to (4) above, the first additive element may be any of B (boron), Al (aluminum), Ga (gallium), P (phosphorus), As (arsenic), or Sb (antimony). Such a first additive element is preferably used in thermoelectric conversion materials in which the base material is composed of SiGe.

[0022] The thermoelectric conversion element of this disclosure comprises a thermoelectric conversion material portion, a first electrode disposed in contact with the thermoelectric conversion material portion, and a second electrode disposed in contact with the thermoelectric conversion material portion but separated from the first electrode. The material constituting the thermoelectric conversion material portion is a thermoelectric conversion material according to any one of (1) to (5) above, whose component composition is adjusted so that the conductivity type is p-type or n-type.

[0023] The thermoelectric conversion element of this disclosure is a thermoelectric conversion material whose component composition is adjusted so that the conductivity type is p-type or n-type, thereby improving the efficiency of the thermoelectric conversion. Therefore, the thermoelectric conversion element of this disclosure can provide a thermoelectric conversion element that improves the efficiency of the thermoelectric conversion.

[0024] The thermoelectric conversion module of this disclosure includes a plurality of the above-mentioned thermoelectric conversion elements. By including a plurality of the thermoelectric conversion elements of this disclosure, which are designed to improve the efficiency of thermoelectric conversion, a thermoelectric conversion module with improved thermoelectric conversion efficiency can be obtained.

[0025] [Details of the embodiments of this disclosure] Next, embodiments of the thermoelectric conversion material of this disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0026] (Embodiment 1) The structure of the thermoelectric conversion material in Embodiment 1 of this disclosure will now be described. Figure 1 is a schematic diagram showing the microstructure of the thermoelectric conversion material in Embodiment 1. Referring to Figure 1, the thermoelectric conversion material 11 according to Embodiment 1 of this disclosure includes a semiconductor base material 12, a first additive element that functions as a dopant, a second additive element different from the first additive element, and oxygen. In this embodiment, the semiconductor base material 12 is SiGe (silicon germanium). The base material 12 includes an amorphous phase. The illustration of the first additive element, the second additive element, O, and N (described later) in Figure 1 is omitted. Note that grain boundaries 13 are shown in Figure 1.

[0027] The first additive element functions as a dopant and is one of B, Al, Ga, P, As, or Sb. Such a first additive element is preferably used in thermoelectric conversion materials in which the base material is composed of SiGe. In this embodiment, it is P and Ge. The second additive element functions as an oxygen getter and contains at least one of Mg, Ca, or Ti. In this embodiment, Mg is used as the second additive element. The thermoelectric conversion material 11 also contains N.

[0028] Here, in a field of view of the cross-section of the base material 12, selected such that the grain boundaries 13 intersect opposite sides of the field of view, the distribution of the second additive element and oxygen have a positive correlation. The correlation coefficient is in the range of 0.2 or more and less than 1.0. Furthermore, the base material 12 includes a first region 16 where the oxygen concentration is a first concentration and a second region 17 where the oxygen concentration is a second concentration higher than the first concentration, in a field of view of 100 nm square to 2 μm square. These will be described in detail later. The difference between the first and second concentrations is 10 at% or more. These will be described in detail later.

[0029] Next, the method for manufacturing the thermoelectric conversion material 11 in Embodiment 1 will be briefly described. First, the raw materials to be prepared are Si and Ge, which are the matrix elements constituting the base material, P and Ge as the first additive elements, and Mg as the second additive element, all in powder form. Here, the second additive element is prepared as Mg-N powder. By doing so, oxidation of Mg during the material preparation stage can be prevented.

[0030] Next, the raw material powder, weighed to achieve the desired composition, is placed into the grinding container along with the milling ball. This process is carried out in a glove box with an inert gas atmosphere to suppress oxidation of the raw material powder. The grinding container is then set into the milling apparatus, and milling is performed. Milling is carried out, for example, at a rotation speed of 100 rpm to 700 rpm for 5 to 10 hours. This milling process mixes and finely grinds the raw material powder.

[0031] Next, the obtained fine powder is filled into a prepared mold (die). Then, the die is placed in a sintering apparatus and a sintered body is formed by the Spark Plasma Sintering method. The temperature at this time can be, for example, 500°C to 1000°C. These steps are also carried out in an inert gas atmosphere by replacing the atmosphere in a glove box or chamber. This yields the thermoelectric conversion material 11 in Embodiment 1. In this thermoelectric conversion material 11, Mg-N powder is used as the second additive element, so the thermoelectric conversion material 11 contains nitrogen. In the above example of manufacturing method, Mg-N powder is used as the second additive element, but the method is not limited to this, and Mg-Si powder may also be used as the second additive element.

[0032] The content of the added elements can be measured, for example, by EDX (Energy Dispersive X-ray Spectrometry). For EDX, a TEM (Transmission Electron Microscope) image of a portion of the thermoelectric conversion material 11 was taken and measured. For TEM image acquisition, a JEM-2800 (manufactured by JEOL Ltd.) was used, with the following measurement conditions: acceleration voltage of 200kV, probe size of 0.5nm, and CL aperture of 3. For atomic detection by EDX, an EDX (manufactured by Thermo Fisher Scientific Inc.) was used, with the following measurement conditions: spot size of 0.5nm, CL aperture of 3, analysis mode set to mapping, and analysis time of 20 minutes. Furthermore, the content of added elements of 0.1at% or less can be measured, for example, by SIMS (Secondary Ion Mass Spectrometry). For the specific measurement method, an ADEPT-1010 (manufactured by ULVAC, Inc.) was used, and the ion source used for measurement was CsR+ ions for the added element R.

[0033] Figure 2 is a TEM image showing a cross-section of the base material 12 and a portion of the obtained thermoelectric conversion material 11. Figure 2 shows the case where Mg is added and x = 3 at% for n-type SiGe. Figure 3 is a figure showing the distribution analysis results of O (oxygen) in TEM / EDX. Figure 4 is a figure showing the distribution analysis results of Mg (magnesium) in TEM / EDX. In Figures 3 and 4, the white areas indicate the state in which each element is present at a high concentration. Referring to Figures 2, 3 and 4 together, grain boundaries 13 can be seen in the base material 12 of the thermoelectric conversion material 11 in Embodiment 1. Referring particularly to Figure 3, a second region 17, which is a region of high oxygen concentration, is located near the grain boundary 13. The region avoiding this grain boundary 13 is the first region 16, which is a region of low oxygen concentration. Also, referring particularly to Figure 4, magnesium is also present at a high concentration near the grain boundary 13. That is, it can be seen that magnesium, which is more easily oxidized than Si, captures oxygen and oxidizes, appearing near the grain boundary 13. Region 18 is a second region 17, which is a region of high oxygen concentration, and is a 100 nm square region in which the grain boundaries 13 are selected to cross opposite edges of the field of view.

[0034] Examples of thermoelectric materials that are outside the scope of this disclosure are described below. Figure 5 is a TEM image showing a portion of a thermoelectric material that does not contain the second additive element, which is outside the scope of this disclosure. Figure 6 is a diagram showing the distribution analysis results of O (oxygen) in TEM / EDX of a thermoelectric material that is outside the scope of this disclosure. The thermoelectric materials shown in Figures 5 and 6 do not contain the second additive element (e.g., Mg), and are otherwise the same as in Embodiment 1. Referring to Figures 5 and 6, in the thermoelectric material that is outside the scope of this disclosure, although grain boundaries 13 exist, oxygen is not concentrated at the grain boundaries 13, and the oxygen concentration is uniformly distributed in all regions. In such a thermoelectric material, the oxygen content is uniformly contained at a ratio of 2.2 at or less. In the thermoelectric conversion material 11 in Embodiment 1 shown in Figures 2 to 4, the oxygen content is high at 15 at% in the second region 17, which is a high-concentration region, but in the first region 16, which is another region, the oxygen content is very low at 0.7 at% or less. This first region 16 with a low oxygen concentration helps to suppress the decrease in conductivity. In other words, in the manufacturing process of thermoelectric conversion materials, no matter how careful one is, oxidation of the fine powder raw material progresses due to oxygen on the order of ppb (parts per billion) contained in the inert gas and minute leaks in the grinding container, etc. However, with the thermoelectric conversion material 11 of this disclosure, the second additive element contained in the material adsorbs the trace amount of oxygen that has been mixed in, preventing oxidation of the base material SiGe itself.

[0035] Figure 7 is a graph showing the relationship between the content percentage and PF when the type and content percentage of the second additive element are varied. In Figure 7, the horizontal axis represents the content percentage x (at%), and the vertical axis represents PF (μW / cmK). 2 ) is shown. Also, Table 1 is a table showing the PF values ​​in Figure 7, along with the content ratio and type of the second additive element.

[0036] [Table 1]

[0037] Referring to Figure 7 and Table 1, for any second additive element, if the content is between 0.5 at% and 5 at%, then PF should be 26 (μW / cmK). 2 ) This allows for the maintenance of a high PF.

[0038] In the above embodiment, Mg was used as the second additive element, but the invention is not limited to Mg; Ca or Ti may also be used as the second additive element. In other words, the second additive element may contain at least one of Mg, Ca, and Ti. Furthermore, the content ratio of the second additive element to the base material may be set to 0.5 at or more and 5 at% or less.

[0039] Figure 8 is a graph showing the correlation coefficients in each region. In Figure 8, the horizontal axis represents each region, and the vertical axis represents the correlation coefficient. Regions 1, 2, 3, and 4 represent the case where Mg is added and n-type SiGe is x=3at% (Sample 1), while regions 5, 6, 7, and 8 represent the case where Mg is added and p-type SiGe is x=3at% (Sample 2). Regions 1, 2, 3, 5, 6, and 7 are the second region 17, which is a high-oxygen concentration region, as shown by region 18 in Figure 3, and are 100 nm square regions selected so that the grain boundaries 13 cross opposite edges of the field of view. Regions 4 and 8 are the first region 16, which avoids the grain boundaries 13, and are 100 nm square regions. Figure 9 is a graph showing the relationship between oxygen concentration and magnesium concentration. In Figure 9, the horizontal axis represents oxygen concentration, and the vertical axis represents magnesium concentration. Figure 9 shows the concentration within the 100 nm square range indicated by region 18 in Figure 3. Table 2 shows the correlation coefficient values ​​for each region of Sample 1 and Sample 2.

[0040] [Table 2]

[0041] The correlation coefficient r is calculated using the following formula (Equation 1), where xi and yi are the concentrations (detected amounts) of O and Mg, respectively, for pixel i.

[0042]

number

[0043] Referring to Figures 8 and 9 and Table 1, first, in Figure 9, it can be seen that the oxygen concentration and magnesium concentration are distributed similarly. That is, when the oxygen concentration is high, the magnesium concentration is also high, and when the oxygen concentration is low, the magnesium concentration is also low. From this, it can be seen that oxygen is adsorbed by magnesium.

[0044] Furthermore, regarding the correlation coefficient, in the field of view of the cross-section of the base material 12, selected such that the grain boundaries 13 cross opposite sides of the field of view (regions 1, 2, 3, 5, 6, and 7), the distribution of the second additive element and oxygen have a positive correlation. If the content of the second additive element is between 0.5 at% and 5 at%, the correlation coefficient of the correlation in the field of view of the cross-section of the base material 12, selected such that the grain boundaries cross opposite sides of the field of view, is in the range of 0.2 to less than 1.0. In fields of view that do not include grain boundaries, i.e., regions 4 and 8, the correlation coefficients are 0.11 and 0.10, respectively. In this way, the second additive element can suppress the widespread distribution of uniform oxygen concentration and concentrate oxygen at the grain boundaries 13. In other words, PF can be increased more reliably, and the efficiency of thermoelectric conversion can be improved.

[0045] (Embodiment 2) Next, a power generation element will be described as one embodiment of a thermoelectric conversion element using the thermoelectric conversion material according to this disclosure.

[0046] Figure 10 is a schematic diagram showing the structure of the π-type thermoelectric element (power generation element), which is the thermoelectric conversion element in this embodiment. For ease of understanding, some of the hatching indicating the cross-section has been omitted in Figure 10.

[0047] Referring to Figure 10, the π-type thermoelectric conversion element 21 comprises a p-type thermoelectric conversion material section 22, an n-type thermoelectric conversion material section 23, a high-temperature side electrode 24, a first low-temperature side electrode 25, a second low-temperature side electrode 26, and wiring 27. The high-temperature side electrode 24 is a first electrode positioned in contact with the thermoelectric conversion material sections 22 and 23. The first low-temperature side electrode 25 is a second electrode positioned in contact with the thermoelectric conversion material section 22 and away from the high-temperature side electrode 24. The second low-temperature side electrode 26 is a second electrode positioned in contact with the thermoelectric conversion material section 23 and away from the high-temperature side electrode 24.

[0048] The material constituting the p-type thermoelectric conversion material section 22 is, for example, the thermoelectric conversion material of Embodiment 1, whose component composition has been adjusted so that the conductivity type is p-type. The material constituting the n-type thermoelectric conversion material section 23 is, for example, the thermoelectric conversion material of Embodiment 1, whose component composition has been adjusted so that the conductivity type is n-type.

[0049] The p-type thermoelectric material section 22 and the n-type thermoelectric material section 23 are arranged side by side with a gap between them. The high-temperature side electrode 24 is positioned to extend from one end 31 of the p-type thermoelectric material section 22 to one end 32 of the n-type thermoelectric material section 23. The high-temperature side electrode 24 is positioned to contact both one end 31 of the p-type thermoelectric material section 22 and one end 32 of the n-type thermoelectric material section 23. The high-temperature side electrode 24 is positioned to connect one end 31 of the p-type thermoelectric material section 22 and one end 32 of the n-type thermoelectric material section 23. The high-temperature side electrode 24 is made of a conductive material, such as a metal. The high-temperature side electrode 24 is in ohmic contact with the p-type thermoelectric material section 22 and the n-type thermoelectric material section 23.

[0050] The thermoelectric conversion material section 22 or thermoelectric conversion material section 23 is preferably p-type or n-type, but either one may be a metal conductor.

[0051] The first low-temperature electrode 25 is positioned in contact with the other end 33 of the p-type thermoelectric conversion material portion 22. The first low-temperature electrode 25 is positioned away from the high-temperature electrode 24. The first low-temperature electrode 25 is made of a conductive material, such as a metal. The first low-temperature electrode 25 is in ohmic contact with the p-type thermoelectric conversion material portion 22.

[0052] The second low-temperature electrode 26 is positioned in contact with the other end 34 of the n-type thermoelectric material portion 23. The second low-temperature electrode 26 is positioned away from the high-temperature electrode 24 and the first low-temperature electrode 25. The second low-temperature electrode 26 is made of a conductive material, such as a metal. The second low-temperature electrode 26 is in ohmic contact with the n-type thermoelectric material portion 23.

[0053] The wiring 27 is made of a conductor such as metal. The wiring 27 electrically connects the first low-temperature electrode 25 and the second low-temperature electrode 26.

[0054] In the π-type thermoelectric conversion element 21, if a temperature difference is formed such that, for example, one end 31 of the p-type thermoelectric conversion material portion 22 and one end 32 of the n-type thermoelectric conversion material portion 23 are at a high temperature, and the other end 33 of the p-type thermoelectric conversion material portion 22 and the other end 34 of the n-type thermoelectric conversion material portion 23 are at a low temperature, then in the p-type thermoelectric conversion material portion 22, p-type carriers (holes) move from one end 31 to the other end 33. At the same time, in the n-type thermoelectric conversion material portion 23, n-type carriers (electrons) move from one end 32 to the other end 34. As a result, current flows through the wiring 27 in the direction of arrow I. In this way, power generation by thermoelectric conversion using the temperature difference is achieved in the π-type thermoelectric conversion element 21. In other words, the π-type thermoelectric conversion element 21 is a power generation element.

[0055] Furthermore, the thermoelectric conversion material 11 of Embodiment 1 is used as the material constituting the p-type thermoelectric conversion material section 22 and the n-type thermoelectric conversion material section 23. As a result, the π-type thermoelectric conversion element 21 becomes a highly efficient power generation element.

[0056] In the above embodiments, a π-type thermoelectric element was described as an example of the thermoelectric element of this disclosure, but the thermoelectric element of this disclosure is not limited to this. The thermoelectric element of this disclosure may be a thermoelectric element having another structure, such as an I-type (unireg-type) thermoelectric element.

[0057] Furthermore, in the above embodiment, the thermoelectric conversion material 11 of Embodiment 1 is used as the material constituting the p-type thermoelectric conversion material section 22 and the n-type thermoelectric conversion material section 23, but this is not limited to this. That is, the thermoelectric conversion material of Embodiment 2 or the thermoelectric conversion material of Embodiment 3 may be used as the material constituting the p-type thermoelectric conversion material section 22 and the n-type thermoelectric conversion material section 23. Note that the material constituting the p-type thermoelectric conversion material section 22 and the material constituting the n-type thermoelectric conversion material section 23 may be different materials.

[0058] (Embodiment 3) By electrically connecting multiple π-type thermoelectric conversion elements 21, a power generation module can be obtained as a thermoelectric conversion module. The power generation module 41, which is a thermoelectric conversion module in this embodiment, has a structure in which multiple π-type thermoelectric conversion elements 21 are connected in series.

[0059] Figure 11 shows an example of the structure of a power generation module. Referring to Figure 11, the power generation module 41 of this embodiment comprises a plurality of p-type thermoelectric conversion material parts 22, a plurality of n-type thermoelectric conversion material parts 23, low-temperature side electrodes 25 and 26 corresponding to the first low-temperature side electrode 25 and the second low-temperature side electrode 26, a high-temperature side electrode 24, a low-temperature side insulating substrate 28, and a high-temperature side insulating substrate 29. The low-temperature side insulating substrate 28 and the high-temperature side insulating substrate 29 are made of ceramic such as alumina. The p-type thermoelectric conversion material parts 22 and the n-type thermoelectric conversion material parts 23 are arranged alternately. The low-temperature side electrodes 25 and 26 are arranged in contact with the p-type thermoelectric conversion material parts 22 and the n-type thermoelectric conversion material parts 23, similar to the π-type thermoelectric conversion element 21 described above. The high-temperature side electrode 24 is arranged in contact with the p-type thermoelectric conversion material parts 22 and the n-type thermoelectric conversion material parts 23, similar to the π-type thermoelectric conversion element 21 described above. The p-type thermoelectric material section 22 is connected to an adjacent n-type thermoelectric material section 23 on one side by a common high-temperature side electrode 24. Furthermore, the p-type thermoelectric material section 22 is connected to an adjacent n-type thermoelectric material section 23 on a side other than the one described above by common low-temperature side electrodes 25 and 26. In this way, all the p-type thermoelectric material sections 22 and n-type thermoelectric material sections 23 are connected in series.

[0060] The low-temperature side insulating substrate 28 is positioned on the main surface side opposite to the side that contacts the p-type thermoelectric conversion material portion 22 and the n-type thermoelectric conversion material portion 23 of the plate-shaped low-temperature side electrodes 25 and 26. One low-temperature side insulating substrate 28 is provided for each of the multiple (all) low-temperature side electrodes 25 and 26. The high-temperature side insulating substrate 29 is positioned on the side opposite to the side that contacts the p-type thermoelectric conversion material portion 22 and the n-type thermoelectric conversion material portion 23 of the plate-shaped high-temperature side electrode 24. One high-temperature side insulating substrate 29 is provided for each of the multiple (all) high-temperature side electrodes 24.

[0061] Wirings 42 and 43 are connected to the high-temperature side electrode 24 or low-temperature side electrode 25, 26 that contact the p-type thermoelectric material section 22 or n-type thermoelectric material section 23 located at either end of the series-connected p-type thermoelectric material section 22 or n-type thermoelectric material section 23. When a temperature difference is formed such that the high-temperature side insulating substrate 29 is at a high temperature and the low-temperature side insulating substrate 28 is at a low temperature, current flows in the direction of arrow I through the series-connected p-type thermoelectric material section 22 and n-type thermoelectric material section 23, similar to the case of the π-type thermoelectric element 21. In this way, power generation by thermoelectric conversion using the temperature difference is achieved in the power generation module 41.

[0062] According to such a power generation module 41, high thermoelectric conversion efficiency can be achieved by including multiple thermoelectric conversion elements 21 of the present disclosure, which have improved thermoelectric conversion efficiency.

[0063] The embodiments disclosed herein should be understood to be illustrative in all respects and not restrictive in any way. The scope of the present invention is defined not by the foregoing description but by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0064] 11 Thermoelectric materials 12 Base materials 13 Grain boundaries 16 First area 17 Second area 18 areas 21 Thermoelectric conversion element 22,23 Thermoelectric Conversion Materials Section 24 High temperature side electrode 25,26 Low-temperature side electrode 27,42,43 Wiring 28 Low-temperature side insulating substrate 29 High-temperature side insulating substrate 31, 32, 33, 34 Ends 41 Power generation module I Arrow

Claims

1. A base material composed of SiGe, The first additive element functions as a dopant, A second additive element different from the first additive element, A thermoelectric conversion material containing oxygen, The second additive element comprises at least one of Mg, Ca, and Ti. The content ratio of the second additive element in the base material is 0.5 at% or more and 5 at% or less. In a field of view of the cross-section of the base material, selected such that the grain boundaries intersect opposite sides of the field of view, the distribution of the second additive element and the oxygen have a positive correlation. The correlation coefficient of the aforementioned correlation is in the range of 0.2 or more and less than 1.

0. A thermoelectric conversion material wherein the second additive element adsorbs the oxygen, and the second additive element and the oxygen aggregate at the grain boundaries, thereby distributing high oxygen concentration regions and low oxygen concentration regions, including the grain boundaries, within the thermoelectric conversion material.

2. In the field of view, which is 100 nm square or larger and 2 μm square or smaller, there is a first region where the oxygen concentration is a first concentration, and a second region where the oxygen concentration is a second concentration higher than the first concentration. The thermoelectric conversion material according to claim 1, wherein the difference between the first concentration and the second concentration is 10 at% or more.

3. The thermoelectric conversion material is the thermoelectric conversion material according to claim 1 or claim 2, wherein the thermoelectric conversion material contains nitrogen.

4. The thermoelectric conversion material according to claim 1 or claim 2, wherein the base material includes an amorphous phase.

5. The thermoelectric conversion material according to claim 1 or claim 2, wherein the first additive element is one of B, Al, Ga, P, As, or Sb.

6. Thermoelectric conversion material section, A first electrode is arranged in electrical contact with the thermoelectric conversion material portion, The thermoelectric conversion material portion is electrically in contact with the second electrode, which is positioned away from the first electrode, and the second electrode is also electrically in contact with the first electrode. A thermoelectric element in which the material constituting the thermoelectric conversion material portion is the thermoelectric conversion material according to claim 1 or claim 2, wherein the composition is adjusted so that the conductivity type is p-type or n-type.

7. A thermoelectric conversion module comprising a plurality of thermoelectric conversion elements as described in claim 6.

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