Thermoelectric conversion member, method for producing same, and thermoelectric conversion element

Abstract

Provided are: a thermoelectric conversion member that can maintain low contact resistance over a long period of time by suppressing Mg diffusion from an Mg3Sb2-based thermoelectric material; a method for producing the same; and a thermoelectric conversion element.　A thermoelectric conversion member according to the present invention comprises: a thermoelectric conversion layer comprising an n-type thermoelectric material including at least magnesium (Mg) and antimony (Sb) and / or bismuth (Bi); and an Mg layer located on at least one end surface of the thermoelectric conversion layer. A method for producing a thermoelectric conversion member according to the present invention includes: forming a laminate of a thermoelectric conversion layer that comprises an n-type thermoelectric material including at least magnesium (Mg) and antimony (Sb) and / or bismuth (Bi), and a raw material that includes Mg as a raw material for an Mg layer; and sintering the laminate.

Description

Thermoelectric conversion member, method for manufacturing the same, and thermoelectric conversion element

[0001] The present invention relates to a thermoelectric conversion member, a method for manufacturing the same, and a thermoelectric conversion element.

[0002] A thermoelectric conversion element that can directly convert heat into electric power and does not emit greenhouse gases is highly expected as a power generation device that can recover waste heat. In addition, thermoelectric conversion elements are also expected as self-powered sources for IoT devices, and improving the thermoelectric conversion efficiency near room temperature is widely desired as a technology to support the rapid development of the IoT society.

[0003] Magnesium antimonide (Mg ３ Sb ２ )-based materials exhibit high performance as n-type thermoelectric materials near room temperature and are expected to be alternative materials to conventional bismuth telluride (Bi ２ Te ３ )-based materials in recent years (see Patent Document 1).

[0004] However, when incorporating Mg ３ Sb ２ -based materials into thermoelectric conversion elements, there remains an issue with the long-term stability of the materials. With long-term use, Mg in the thermoelectric material diffuses into the electrode material or the metal layer or diffusion barrier layer inserted between the thermoelectric material and the electrode, resulting in a problem that the thermoelectric properties deteriorate.

[0005] In contrast, Non-Patent Document 1 discloses using Fe and 304 stainless steel as barrier layers in a thermoelectric conversion element using a Mg ３ Sb ２ -based thermoelectric material. However, in Non-Patent Document 1, the contact resistance between the barrier layer and the thermoelectric material continuously increases with long-term high-temperature holding, and finally a high resistance value exceeding 10 μΩcm ２ has been confirmed.

[0006] In Non-Patent Document 2, Mg ３ Sb ２In thermoelectric conversion elements using thermoelectric materials, the use of Fe foil as a diffusion barrier layer for Mg has been disclosed. While the Fe foil can suppress the diffusion of Mg, after long-term use of about 30 days, the thermoelectric properties still tend to deteriorate over time.

[0007] Thus, conventionally, Mg ３ Sb ２ In thermoelectric conversion elements using thermoelectric materials, there has been a need for an electrode interface design that can suppress Mg diffusion and maintain low contact resistance over the long term.

[0008] International Publication No. 2022 / 054577

[0009] Li Yin et al. , Reliable n-type Mg3.2Sb1.5Bi0.49Te0.01 / 304 stainless steel junction for thermoelectric applications, Acta Materialia 198 (2020) 25-34. Nuo Qu et al. ,Interfacial design contributing to high conversion efficiency in Mg3(Sb,Bi)2 / Bi2Te3 thermoelectric module with superior stability, Advanced Energy Materials (2023) 2302818.

[0010] From the above, the object of the present invention is Mg ３ Sb ２ The objective is to provide a thermoelectric conversion member, a method for manufacturing the same, and a thermoelectric conversion element that can suppress the diffusion of Mg from the thermoelectric material and maintain low contact resistance over the long term.

[0011] In embodiments of the present invention, according to one view, the thermoelectric conversion member may comprise a thermoelectric conversion layer made of an n-type thermoelectric material containing at least magnesium (Mg) and antimony (Sb) and / or bismuth (Bi), and an Mg layer located on at least one end face of the thermoelectric conversion layer. The above problems are solved. In any of the thermoelectric conversion members described above, the n-type thermoelectric material is Mgａ Sb ２－ｂ－ｃ Bi ｂ M ｃ Z d The thermoelectric conversion member contains an inorganic compound represented by , where M is selenium (Se) and / or tellurium (Te), Z is at least one element selected from the group consisting of indium (In), molybdenum (Mo), copper (Cu), cobalt (Co), and manganese (Mn), and parameters a, b, c, and d may satisfy 3 ≤ a ≤ 3.5, 0 ≤ b ≤ 2, 0 ≤ c ≤ 0.1, and 0 ≤ d ≤ 0.1. In any of the thermoelectric conversion members described above, the thickness of the Mg layer may be 1 μm or more and 1000 μm or less. In any of the thermoelectric conversion members described above, the thermoelectric conversion layer and the Mg layer may be sintered bodies. In any of the thermoelectric conversion members described above, the Mg layer is P6 ３It may belong to the space group / mmc. In any of the thermoelectric conversion members described above, the Mg layer may be located on both ends of the thermoelectric conversion member. In any of the thermoelectric conversion members described above, a metal layer may be further provided on the end face of the Mg layer that is not in contact with the n-type thermoelectric conversion layer. In any of the thermoelectric conversion members described above, the metal layer may consist of a Ni layer. In any of the thermoelectric conversion members described above, the Mg layer may further contain at least one element selected from the group consisting of iron (Fe), niobium (Nb), and molybdenum (Mo). In any of the thermoelectric conversion members described above, the content of the element added to the Mg layer may be less than 10 at%. In embodiments of the present invention, with respect to any of the thermoelectric conversion members described above, from another viewpoint, the method for manufacturing the thermoelectric conversion member may include forming a laminate of a thermoelectric conversion layer made of an n-type thermoelectric material containing magnesium (Mg) and antimony (Sb) and / or bismuth (Bi), and a raw material containing Mg as a raw material for the Mg layer, and sintering the laminate. The above problems are solved. In the method for manufacturing any of the thermoelectric conversion members described above, the sintering may include discharge plasma sintering. In the method for manufacturing any of the thermoelectric conversion members described above, the sintering may include sintering the laminate at a temperature range of 673K ​​to 973K and a pressure range of 40MPa to 80MPa. In the method for manufacturing any of the thermoelectric conversion members described above, the sintering may include sintering the laminate at a temperature range of 723K to 823K and a pressure range of 50MPa to 70MPa for a time of 5 minutes to 20 minutes. In any of the above-described methods for manufacturing thermoelectric conversion members, the sintering may include sintering the laminate at 773 K and 60 MPa for 10 minutes.In embodiments of the present invention, according to another view, a method for manufacturing any of the thermoelectric conversion members described above may include forming an Mg layer on at least one end face side of a thermoelectric conversion layer made of an n-type thermoelectric material containing magnesium (Mg) and antimony (Sb) and / or bismuth (Bi) by at least one method selected from the group consisting of physical vapor deposition, chemical plating, and electroplating. The above problems are solved. In a method for manufacturing any of the thermoelectric conversion members described above, the formation of the Mg layer may be performed by magnetron sputtering. In embodiments of the present invention, according to yet another view, a thermoelectric power generation element is a thermoelectric power generation element comprising at least an n-type thermoelectric conversion member, wherein the n-type thermoelectric conversion member may be any of the thermoelectric conversion members described above. The above problems are solved. Any of the thermoelectric conversion elements described above may further comprise p-type thermoelectric conversion members alternately connected in series with the n-type thermoelectric conversion members. In any of the thermoelectric conversion elements described above, the p-type thermoelectric conversion member is MgAgSb-based, BiTeSe-based, GeTe-based, or AgSbTe. ２ CdSb system, CdSb system, and CoSb ３ It may include a p-type thermoelectric material selected from the group consisting of systems.

[0012] The thermoelectric conversion member of the present invention is Mg ３ Sb ２ By providing an Mg layer on at least one end face side of a thermoelectric conversion layer made of a thermoelectric material, ３ Sb ２ The diffusion of Mg from the thermoelectric material can be suppressed. Low contact resistance can be maintained over the long term. Furthermore, by using the thermoelectric conversion member of the present invention, electrode contact resistance can be reduced. A thermoelectric conversion element with improved thermoelectric conversion efficiency can be provided.

[0013] In the embodiments of the present invention, the manufacturing method is Mg ３ Sb ２ The process may include forming a laminate of a thermoelectric conversion layer made of a thermoelectric material and a raw material for the Mg layer, and then sintering it. This allows for the production of a thermoelectric conversion element with high thermoelectric conversion efficiency through a simple process while suppressing the evaporation of Mg.

[0014] Schematic diagram showing the n-type thermoelectric conversion member according to this embodiment Schematic diagram showing the n-type thermoelectric conversion member according to this embodiment Schematic diagram showing another form of the n-type thermoelectric conversion member Schematic diagram showing another form of the n-type thermoelectric conversion member Flowchart showing an exemplary manufacturing process of the thermoelectric conversion member according to this embodiment Schematic diagram showing a sintering method for a laminate Schematic diagram showing a single-element thermoelectric conversion element Schematic diagram showing a π-type thermoelectric conversion element SEM image showing the interface of the thermoelectric conversion member in Example 1 Figure 7 showing the EDX mapping of Mg Figure 7 showing the EDX mapping of Sb Figure 7 showing the EDX mapping of Bi Figure 7 showing the EDX mapping of Ni Figure 7 showing the interface of the thermoelectric conversion member in Example 5 Figure 12 showing the EDX mapping of Mg Figure 12 showing the EDX mapping of Sb Figure 12 showing the EDX mapping of Bi Figure 12 showing the EDX mapping of Ni Figure 12 showing Mg ３ Sb ２ Figure 17A shows how the EDX line scan of Mg, Sb, Bi, and Ni in a thermoelectric material system / Mg layer / Ni layer was performed. Figure 5 shows the Mg layer. ３ Sb ２ Figures showing the annealing time dependence of contact resistivity in thermoelectric conversion members of Mg, Sb, Bi, and Ni in a thermoelectric material / Mg layer / Ni layer, for EDX line scan examples 1 to 5. ３ Sb ２ Figure 1 shows the position dependence of resistance in a thermoelectric material. Schematic Figure 5 shows a π-type two-pair thermoelectric element using the thermoelectric conversion member. Schematic Figure 1 shows a π-type two-pair thermoelectric element using the thermoelectric conversion member. Graph showing the thermoelectric conversion efficiency η of the π-type two-pair thermoelectric element (Example 6) using the thermoelectric conversion member in Example 1. Graph showing the thermoelectric conversion efficiency η of the π-type two-pair thermoelectric element (Example 7) using the thermoelectric conversion member in Example 5.

[0015] Embodiments of the present invention will be described below with reference to the drawings. Similar elements will be given the same number, and their descriptions will be omitted. Furthermore, the drawings only schematically show the shape, size, and arrangement of the components to the extent that the invention can be understood, and the present invention is not limited thereto.

[0016] <Regarding the power generation efficiency of thermoelectric elements and the contact resistance of the barrier layer> The power generation efficiency of thermoelectric elements is mainly determined by the dimensionless figure of merit ZT value of the material, and the dimensionless figure of merit ZT value of the material is shown in Equation 1. Here, S is the Seebeck coefficient, δ is the electrical conductivity, T is the absolute temperature, and k is the thermal conductivity.

[0017] Conventionally, to improve the bonding characteristics between thermoelectric materials and electrodes and reduce contact resistance, it has been considered to provide a barrier layer between the thermoelectric material and the electrode. This barrier layer is also sometimes referred to as a metallization layer, metallization layer, metal layer, thermoelectric interface material TeiM (Thermoelectric Interface Material), intermediate layer, or electrode bonding layer.

[0018] The barrier layer is also used to suppress elemental diffusion from the thermoelectric material and maintain low resistance during long-term power generation. In this case, the thermoelectric conversion element has a sandwich structure of "barrier layer / thermoelectric material / barrier layer," in which the thermoelectric material is sandwiched between two barrier layers.

[0019] Generally, the dimensionless figure of merit ZT is a characteristic factor of thermoelectric conversion elements. ｌｅｇ The value is given by Equation 2, using the dimensionless figure of merit ZT of the material. L is the length of the thermoelectric material, δ is the electrical conductivity, ρ ｃ This is the contact resistivity between the thermoelectric material and the barrier layer.

[0020] Therefore, one of the most important requirements for the barrier layer is a low contact resistivity ρ between it and the thermoelectric material. ｃ It will come to have.

[0021] Traditionally, generally, Mg ３ Sb ２ In thermoelectric conversion elements using thermoelectric materials, Fe is used as the barrier layer material. However, as mentioned above, there is a need to explore materials other than Fe in terms of long-term stability and suppression of Mg diffusion.

[0022] The inventor of this application, Mg ３ Sb ２In order to further improve the thermoelectric conversion efficiency (power generation efficiency) of thermoelectric conversion elements using thermoelectric materials, we sought a more suitable barrier layer material and devised and demonstrated a magnesium (Mg) barrier layer.

[0023] Mg is highly reactive and has a high vapor pressure, making it easily evaporate when heated, thus making it unsuitable for film formation by soldering or thermal spraying. Given this technical background, to the best of the inventors' knowledge, no one had previously conceived of using Mg as a barrier layer. In contrast, the inventors, through trial and error, conceived of a thermoelectric conversion member and its manufacturing method according to this embodiment, and confirmed the effects shown in the examples. Preferred embodiments are described below.

[0024] (First Embodiment) In the first embodiment, a thermoelectric conversion member and a method for manufacturing the same will be described.

[0025] <Thermoelectric Conversion Member> Figures 1A and 1B are schematic diagrams showing the n-type thermoelectric conversion member 100 according to this embodiment.

[0026] As shown in Figure 1A, the n-type thermoelectric conversion member 100 according to this embodiment comprises an n-type thermoelectric conversion layer 110 and an Mg layer 120 located on at least one end face side of the n-type thermoelectric conversion layer 110. The n-type thermoelectric conversion layer 110 is made of an n-type thermoelectric material containing at least magnesium (Mg) and antimony (Sb) and / or bismuth (Bi).

[0027] In this specification, an n-type thermoelectric material comprising at least magnesium (Mg) and antimony (Sb) and / or bismuth (Bi) contains at least an inorganic compound comprising Mg and Sb and / or Bi, and Mg ３ Sb ２ This is called a thermoelectric material.

[0028] Mg ３ Sb ２ Mg, which constitutes the thermoelectric material ３ Sb ２ The system crystal is preferably La ２ O ３It has a type structure and belongs to the P-3m1 space group (the 164th in the International Tables for Crystallography). In this specification, "-3" represents "3 with an overbar".

[0029] Mg ３ Sb ２ The thermoelectric material is not particularly limited as long as it has the elements, crystal structure, and space group described above. Mg ３ Sb ２ As an example of a thermoelectric material, a material may be used in which a portion of the Sb site is substituted with at least one element selected from the group consisting of bismuth (Bi), selenium (Se), and tellurium (Te) using a solid solution. Furthermore, Mg ３ Sb ２ As an example of a thermoelectric material, La ２ O ３ The mold structure may use a material in which at least one element selected from the group consisting of indium (In), molybdenum (Mo), copper (Cu), cobalt (Co), and manganese (Mn) is dissolved in solid solution.

[0030] The Mg layer 120 can reduce the contact resistance between the n-type thermoelectric conversion layer 110 and the electrodes (for example, electrodes 540 and 550, which will be described later in Figure 5). The Mg layer 120 can suppress the thermal diffusion of Mg from the n-type thermoelectric conversion layer 110 towards the electrodes. The Mg layer 120 is a barrier layer.

[0031] Preferably, the Mg layer 120 is a layer of pure Mg. Alternatively, the Mg layer 120 is a layer mainly composed of Mg. If the Mg layer 120 contains elements other than Mg, it is sufficient that the content of Mg is the highest among the components of the layer. Other components other than Mg may be, for example, unavoidable impurities that may be contained in the raw materials. Note that, as will be described later, Mg ３ Sb ２When the thermoelectric material and the Mg layer are formed as flexible layers, the Mg layer may be a mixture of a material mainly composed of Mg and an organic material. Here, "main component" may mean the main component (mol%) that makes up the object in question. Specifically, it may mean a component that makes up 50 mol% or more, or a component that has the highest mol% compared to others.

[0032] As shown in Figure 1A, the Mg layer 120 may be formed on one end face of the n-type thermoelectric conversion layer 110, or as shown in Figure 1B, it may be formed on both end faces of the n-type thermoelectric conversion layer 110. From the viewpoint of reducing contact resistance, a thermoelectric conversion member having Mg layers 120 on both end faces, as shown in Figure 1B, is preferred. Figures 1A and 1B show an example of a long member along the lamination direction, but the n-type thermoelectric conversion member 100 is not limited to this shape, and may be a large-area flat plate shape, for example, so that multiple thermoelectric conversion members can be manufactured at once and cut out for use.

[0033] As described above, the n-type thermoelectric conversion member 100 of this embodiment can suppress the diffusion of Mg from the n-type thermoelectric conversion layer 110 by providing an Mg layer 120 on at least one end face side of the n-type thermoelectric conversion layer 110 made of n-type thermoelectric material. This can maintain the stability of the constituent materials of the thermoelectric conversion element over a long period of time and keep the contact resistance low. Furthermore, because the contact resistance can be kept low, it is possible to maintain a high characteristic factor of the thermoelectric conversion element, as explained using Equation 2. This makes it possible to provide a thermoelectric conversion element that can maintain a high thermoelectric conversion efficiency over a long period of time.

[0034] More preferably, the n-type thermoelectric material used in the n-type thermoelectric conversion layer 110 is Mg ａ Sb ２－ｂ－ｃ Bi ｂ M ｃ Z dIt contains an inorganic compound represented by , where M is selenium (Se) and / or tellurium (Te). Z is at least one element selected from the group consisting of indium (In), molybdenum (Mo), copper (Cu), cobalt (Co), and manganese (Mn). Parameters a, b, c, and d preferably satisfy 3 ≤ a ≤ 3.5, 0 ≤ b ≤ 2, 0 ≤ c ≤ 0.1, and 0 ≤ d ≤ 0.1. For example, it may be 2.9 ≤ a, 3 ≤ a, or 3.1 ≤ a. Alternatively, it may be a ≤ 3.4, a ≤ 3.5, or a ≤ 3.6. Also, b = 0, 0.0001 ≤ b, or 0.001 ≤ b. Also, b ≤ 1.9, b ≤ 2, or b ≤ 2.1. Also, c = 0, 0.0001 ≤ c, or 0.001 ≤ c. Also, c ≤ 0.09, c ≤ 0.1, or c ≤ 0.11. Also, d = 0, 0.0001 ≤ d, or 0.001 ≤ d. Also, d ≤ 0.09, d ≤ 0.1, or d ≤ 0.11.

[0035] Having such a composition, the electrical conductivity and power factor of Mg are improved, particularly in the relatively low temperature range from near low temperatures (temperature range of 273K to 573K) to the medium temperature range (temperature range of 573K to approximately 723K). ３ Sb ２ We can provide thermoelectric materials.

[0036] Preferably, Te is used as the element M. This provides a thermoelectric material with improved electrical conductivity at room temperature and an improved power factor.

[0037] Furthermore, preferably, In is used as the element Z. This provides a thermoelectric material with improved electrical conductivity at room temperature and an improved power factor. ([Reference 1] Longquan Wang et al., High-performance Mg ３ Sb ２-based thermoelectrics with reduced structural disorder and microstructure evolution, Nature Communications (2024) 15:6800. )

[0038] More preferably, Te is used as element M and In as element Z. A suitable example is a = 3.2, b = 1.4, c = 0.005, and d = 0.02. This provides a thermoelectric material with improved electrical conductivity at room temperature and an improved power factor.

[0039] The Mg layer 120 may contain at least one element selected from the group consisting of iron (Fe), niobium (Nb), and molybdenum (Mo). By adding a metallic element that is considered to have high thermal stability at the interface and good electrical conductivity, contact resistance can be further reduced.

[0040] Preferably, the content of the element added to the Mg layer 120 should be greater than 0 at% and less than 10 at% relative to the Mg of the matrix phase. For example, it may be 0.0001 at% or more, 0.001 at% or more, or 0.01 at% or more. It may also be 15 at% or less, 10 at% or less, or 9 at% or less. This allows for a reduction in contact resistance while maintaining a high Mg diffusion prevention effect.

[0041] Preferably, the thickness of the Mg layer 120 is 1 μm or more and 1000 μm or less. More preferably, the thickness of the Mg layer 120 is 5 μm or more and 100 μm or less. For example, it may be 0.9 μm or more, 1 μm or more, or 5 μm or more. It may also be 2000 μm or less, 1000 μm or less, or 500 μm or less. It is possible to maintain stable low contact resistance even under long-term power generation conditions.

[0042] Preferably, the Mg layer 120 is P6 ３ It belongs to the space group / mmc (the 194th entry in the International Tables for Crystallography). It can maintain stable low contact resistance even under long-term power generation conditions.

[0043] Preferably, the n-type thermoelectric conversion layer 110 and the Mg layer 120 are sintered bodies. That is, the Mg layer 120 is preferably integrally molded with the n-type thermoelectric conversion layer 110 by sintering it in contact with the n-type thermoelectric conversion layer 110. This forms a good interface and can further reduce the interfacial contact resistance.

[0044] Figures 2A and 2B are schematic diagrams showing another form of the n-type thermoelectric conversion member 200.

[0045] The n-type thermoelectric conversion member 200 may further include a metal layer 130 on the end face of the Mg layer 120 that is not in contact with the n-type thermoelectric conversion layer 110. As an example, the metal layer 130 may be a single metal with high conductivity such as Ni or Cu. An alloy may also be used as the metal layer 130.

[0046] As shown in Figure 2A, when the Mg layer 120 is provided on one end face side of the n-type thermoelectric conversion layer 110, the n-type thermoelectric conversion member 200 has a three-layer structure of metal layer 130 / Mg layer 120 / n-type thermoelectric conversion layer 110. Also, as shown in Figure 2B, when the Mg layer 120 is provided on both end faces side of the n-type thermoelectric conversion layer 110, it has a five-layer structure of metal layer 130 / Mg layer 120 / n-type thermoelectric conversion layer 110 / Mg layer 120 / metal layer 130. Thus, the n-type thermoelectric conversion member 200 has a structure in which the Mg layer 120 is covered with the metal layer 130.

[0047] In this way, by coating the Mg layer 120 with the metal layer 130, exposure of the Mg layer 120 to the atmosphere is avoided, oxidation of Mg is suppressed, and the stability of the Mg layer 120 can be improved. As a result, the effect of preventing Mg diffusion can be provided stably over a long period of time.

[0048] In addition, as another configuration, the n-type thermoelectric conversion layer 110 is made of Mg ３ Sb ２ The system is composed of a mixture of a thermoelectric material and an organic material, and the Mg layer 120 may be composed of a mixture of a material mainly composed of Mg and an organic material. This allows both the n-type thermoelectric conversion layer 110 and the Mg layer 120 to be formed as flexible layers.

[0049] <Method for Manufacturing Thermoelectric Conversion Members> Figure 3 is a flowchart showing an exemplary manufacturing process for a thermoelectric conversion member according to this embodiment.

[0050] The method according to this embodiment includes steps S310 to S340. ３ Sb ２ When using commercially available thermoelectric materials, steps S310 and S320 may be omitted, and the commercially available Mg ３ Sb ２ The thermoelectric material can be used in step S330.

[0051] In step S310, the raw materials for the n-type thermoelectric conversion layer 110, which consist of an n-type thermoelectric material containing at least magnesium (Mg) and antimony (Sb) and / or bismuth (Bi), are mixed.

[0052] As raw materials for the n-type thermoelectric conversion layer 110, a raw material containing Mg, a raw material containing Sb, and / or a raw material containing Bi may be used. The raw material containing Mg may be powder of elemental Mg metal, or elemental Mg metal in any of the following forms: sheet, granules, or lumps. The raw material containing Sb may be powder of elemental Sb metal, or elemental Sb metal in any of the following forms: sheet, granules, or lumps. The raw material containing Bi may be powder of elemental Bi metal, or elemental Bi metal in any of the following forms: sheet, granules, or lumps.

[0053] The composition of the n-type thermoelectric material is explained with reference to Figures 1A and 1B, and includes Mg ３ Sb ２ Since it is the same as a thermoelectric material, the explanation will be omitted, but you may refer to, for example, Reference 1 mentioned above.

[0054] Raw materials containing Mg, raw materials containing Sb, raw materials containing Bi, and raw materials containing other additive elements, the amount of each element is as described above for Mg. ３ Sb ２ After being weighed to meet the composition ratio requirements for the thermoelectric material system, the materials are mixed, and then further mixed and pulverized by ball milling.

[0055] The raw material mixture for the n-type thermoelectric material may further contain at least one raw material selected from the group consisting of raw materials containing Se, raw materials containing Te, raw materials containing In, raw materials containing Mo, raw materials containing Cu, raw materials containing Co, and raw materials containing Mn as added elements. These added elemental raw materials may be powders of the respective metals, or metals in any of the following forms: sheet, granules, or lumps.

[0056] In step S320, the raw material mixture for the n-type thermoelectric conversion layer 110, which was mixed in step S310, is sintered.

[0057] The sintering in step S320 may be carried out by any method such as discharge plasma sintering (SPS), hot press sintering (HP), or hot isostatic press sintering (HIP). Preferably, it is carried out by discharge plasma sintering (SPS). This makes it possible to obtain a sintered body of thermoelectric material with suppressed grain growth in a short time without using a sintering aid.

[0058] Preferably, the sintering temperature in step S320 is between 900K and 1100K. Furthermore, preferably, SPS is performed within a temperature range of 900K to 1100K and a pressure range of 50MPa to 70MPa. This allows Mg ３ Sb ２ The sintering of the thermoelectric material is accelerated, allowing the n-type thermoelectric conversion layer 110 to be densified in a short time, while also suppressing the volatilization of Mg.

[0059] More preferably, the sintering in step S320 is carried out by SPS at 973K and 60MPa, and more preferably, the sintering time is within 10 minutes. This makes it possible to obtain a sintered body of n-type thermoelectric material with higher density and higher quality in a shorter time.

[0060] Furthermore, if a commercially available n-type thermoelectric material (sintered body) that has been pre-mixed in a predetermined component ratio is used, steps S310 and S320 may be omitted, and the commercially available n-type thermoelectric material may be used in the next step S330.

[0061] In step S330, a laminate is formed of the sintered body of the n-type thermoelectric material obtained in step S320 (i.e., the n-type thermoelectric conversion layer) and a raw material containing Mg as the raw material for the Mg layer.

[0062] In step S330, the raw material for the Mg layer may be a powder of elemental Mg metal, or it may be elemental Mg metal in the form of a sheet, granules, or lumps. The raw material for the Mg layer may also further contain at least one raw material selected from the group consisting of a raw material containing Fe, a raw material containing Nb, and a raw material containing Mo. These raw materials may also be powders of their respective elemental metals, or they may be elemental metals in the form of a sheet, granules, or lumps. It is preferable that the elements added to the Mg layer be in the range of 0.1 at% or more and less than 10 at%.

[0063] Preferably, in step S330, in addition to the two-layer structure of the raw materials for the n-type thermoelectric conversion layer 110 and the Mg layer 120, a three-layer laminate (see Figure 2A) or a five-layer laminate (see Figure 2B) is formed by further laminating the raw material for the metal layer 130. The raw material for the metal layer 130 may be any raw material containing the metal, for example, Ni and / or Cu powder, and may be in any of the following forms: sheet, granules, or lumps.

[0064] Figure 4 is a schematic diagram showing the sintering method of the laminate when manufacturing the n-type thermoelectric conversion member 200 shown in Figure 2B.

[0065] A preferred example of step S330 will be explained using Figure 4. First, the Ni layer material 430 is placed on the upper surface of the punch 440 fitted into the die 460 for pressure molding, and its surface is smoothed. Smoothing the surface of the Ni layer material 430 may mean that the layers to be further laminated on it will make surface contact with the Ni layer after molding, and that no significant irregularities or voids will occur between the layers. Hereafter, it can be understood that the same process of smoothing the material for each layer is performed. Smoothing the surface of the material before layer formation may include operations such as leveling the surface while observing it visually. Such smoothing may be a normal process operation that is generally performed when laminating layers such as barrier layers. The purpose may be to ensure uniform contact between layers and to facilitate pressing and sintering in subsequent processes. In this way, it may mean that after molding, each layer will make surface contact and that no significant irregularities or voids will occur between the layers. In the specification of this application, it is considered that contact electrical resistance and thermal resistance are mainly determined by the material, composition, and pressurization / sintering conditions of layers such as barrier layers. It is considered that smoothing itself does not directly define these properties. For example, it can be smoothed so that a good and clear bonding interface can be obtained as described later. On top of that, the raw material 420 for the Mg layer is added and its surface is smoothed. Furthermore, the n-type thermoelectric conversion layer 410 is placed on top of that so that its upper and lower end faces are parallel to the surface of the raw material 420 for the Mg layer. As the n-type thermoelectric conversion layer 410, a sintered body of the n-type thermoelectric conversion layer obtained in step S320 or a commercially available n-type thermoelectric conversion layer can be used. As shown in Figure 2A, when the Mg layer 120 is formed only on one end face of the n-type thermoelectric conversion layer 110, a laminate with a three-layer structure of the raw material 430 for the Ni layer, the raw material 420 for the Mg layer, and the n-type thermoelectric conversion layer 410 can be formed as described above. Generally speaking, if there are areas exceeding ±1% of the target layer thickness (e.g., the average value), it may be considered significant unevenness. If the tolerance is higher, it may be considered significant unevenness if it exceeds ±5%. Furthermore, if significant changes occur in contact electrical resistance or thermal resistance, it may be said that significant unevenness or voids are present.

[0066] As shown in Figure 2B, when forming Mg layers 120 on both end faces of the n-type thermoelectric conversion layer 110, the lamination of raw materials is continued. That is, as shown in Figure 4, the raw material 420 for the Mg layer is placed on the end face exposed above the n-type thermoelectric conversion layer 410, and its surface is smoothed. Then, the raw material 430 for the Ni layer is placed on top of that, and its surface is smoothed. This forms a five-layer laminate.

[0067] After forming the laminate, the punch 450 is fitted into the die 460, and the machine is set up to perform pressure molding.

[0068] Returning to Figure 3, in step S340, the laminate formed in S330 is sintered. The sintering in step S340 may be carried out by any method such as discharge plasma sintering (SPS), hot press sintering (HP), or hot isostatic press sintering (HIP). Preferably, it is carried out by discharge plasma sintering (SPS). This makes it possible to obtain a sintered body of thermoelectric material with suppressed grain growth in a short time without using a sintering aid, and to obtain an interface with good bonding characteristics.

[0069] Preferably, the sintering temperature in step S340 is in the temperature range of 673K ​​to 973K. The sintering in step S340 is preferably carried out in the pressure range of 40MPa to 80MPa. More preferably, it is carried out within these temperature and pressure ranges.

[0070] More preferably, the sintering in step S340 is carried out by SPS, at a temperature range of 723K to 823K, at a pressure range of 50MPa to 70MPa, for a time of 5 minutes to 20 minutes. In this way, Mg ３ Sb ２ A good interfacial bond can be formed between the thermoelectric conversion layer and the Mg layer.

[0071] More preferably, the sintering in step S340 is carried out by SPS at approximately 773 K and approximately 60 MPa for approximately 10 minutes. In this way, a good interfacial bond is formed between the n-type thermoelectric conversion layer and the Mg layer, and the evaporation of Mg is further suppressed, allowing for the efficient formation of a high-quality thermoelectric conversion element in a short time.

[0072] Mg ３ Sb ２ The optimal temperature for sintering the thermoelectric material is considered to be relatively high, between 900K and 1100K. Furthermore, within this temperature range, if the n-type thermoelectric conversion layer and the Mg layer are sintered in a single step, the Mg is likely to evaporate. In the manufacturing method of this embodiment described above, the raw materials for the Mg layer are laminated onto an already high-temperature sintered n-type thermoelectric conversion layer to form a laminate, which is then sintered at a relatively low temperature within the laminated container to obtain an n-type thermoelectric conversion member. This simple process of pre-sintering the n-type thermoelectric conversion layer suppresses Mg evaporation, allowing for the formation of a good bonding interface between the n-type thermoelectric conversion layer and the Mg layer.

[0073] Furthermore, by laminating the raw material for the metal layer onto the surface of the Mg layer, a metal layer that functions as both a protective layer for the Mg layer and an electrical junction layer with the electrode can be obtained in a single sintering process. In this way, the manufacturing process of the n-type thermoelectric conversion member 200 (see Figures 2A and 2B) can be simplified, and manufacturing costs can be reduced.

[0074] Furthermore, after step S340, the sintered body obtained by sintering the laminate may be annealed in a vacuum. The annealing temperature may be in the range of 500K to 700K, for a period of 5 minutes to 30 days. This may provide a more stable thermoelectric conversion member.

[0075] As described above, according to the manufacturing method of this embodiment, a thermoelectric conversion element with high thermoelectric conversion efficiency can be manufactured efficiently through a simple process.

[0076] Furthermore, the method for manufacturing an n-type thermoelectric conversion member with a bonded Mg layer is not limited to the method described above. Other examples include Mg ３ Sb ２ The above-mentioned Mg layer may be formed on at least one end face of the thermoelectric conversion layer by at least one method selected from the group consisting of physical vapor deposition, chemical plating, and electroplating. The physical vapor deposition method may be vapor deposition, sputtering, molecular beam epitaxy, ion plating, etc. Alternatively, the Mg layer may be formed on both end faces of the thermoelectric conversion layer.

[0077] Similarly, a metal layer (e.g., Ni layer) covering the Mg layer may be formed on the surface layer of the Mg layer by at least one method selected from the group consisting of physical vapor deposition, chemical plating, and electroplating. The physical vapor deposition method may be evaporation, sputtering, molecular beam epitaxy, ion plating, or the like. When the Mg layers are provided on both sides of the thermoelectric conversion layer, metal layers may be formed on the surface layer side of each Mg layer, i.e., on the end face side opposite to the thermoelectric conversion layer.

[0078] Preferably, the Mg layer and the metal layer may be formed by magnetron sputtering. In this way, the Mg layer and the metal layer with good smoothness can be efficiently formed.

[0079] In the above description, the n-type thermoelectric conversion layer is a sintered body, and the form of forming the Mg layer on the sintered body has been described. As another form, the n-type thermoelectric conversion layer, the Mg layer, and the metal layer may each be flexible.

[0080] That is, the n-type thermoelectric conversion layer may be composed of a mixture of an Mg ３ Sb ２ -based n-type thermoelectric conversion material and an organic material, and may be a flexible layer. Similarly, the Mg layer may be composed of a mixture of a material mainly composed of Mg and an organic material, and may be a flexible layer. In addition, the metal layer (e.g., Ni layer) may also be composed of a mixture of a material mainly composed of a metal (e.g., Ni and / or Cu) and an organic material, and may be a flexible layer.

[0081] [[ID=十六]] Here, the organic material may be at least one organic material selected from the group consisting of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT), polyaniline (PANI), tetrathiafulvalene (TTF), and benzodifurandione paraphenylenevinylene (BDPPV). These are organic materials that can provide a flexible layer. <00003 sixty]] <00003 sixty-one]] Note that Mg ３ Sb ２The thermoelectric material, the material mainly composed of Mg, and the material mainly composed of Ni and / or Cu are preferably present in amounts of 4 wt% to 80 wt% relative to the above-mentioned organic material. More preferably, they are present in amounts of 4 wt% to 50 wt%, even more preferably 4 wt% to 10 wt%, and even more preferably 4 wt% to 7 wt%. In this way, a film-type thermoelectric conversion member with more effective flexibility can be provided.

[0083] A flexible film-type n-type thermoelectric conversion member may be manufactured by simply laminating a flexible n-type thermoelectric conversion layer and a flexible Mg layer. Alternatively, a flexible film-type n-type thermoelectric conversion member may be manufactured by simply laminating a flexible n-type thermoelectric conversion layer, a flexible Mg layer, and a flexible metal layer (Ni and / or Cu).

[0084] (Second Embodiment) In the second embodiment, a thermoelectric conversion element using the n-type thermoelectric conversion member 200 of the first embodiment (see Figures 2A and 2B) will be described. In the following, examples of applying the n-type thermoelectric conversion member 200 to a single element or a π-type thermoelectric conversion element will be shown, but the embodiments are not limited to these examples, and the n-type thermoelectric conversion members 100 and 200 may be incorporated into other types of thermoelectric conversion elements.

[0085] Figure 5 is a schematic diagram showing a single-element thermoelectric conversion element 500.

[0086] As shown in Figure 5, the thermoelectric element 500 of this embodiment comprises at least one n-type thermoelectric member 200. The thermoelectric element 500 also comprises electrodes 540 and 550 on each end face of the n-type thermoelectric member 200, i.e., on the surface of the metal layer 130. The electrodes 540 and 550 may include general electrode materials, such as Fe, Ag, Al, Ni, Cu, etc. In the example in Figure 5, the electrode 550, which will be the low-temperature side, is joined to the first end face (the lower end face in the figure) of the n-type thermoelectric member 200 by solder or the like. The electrode 540, which will be the high-temperature side, is joined to the second end face (the upper end face in the figure) of the n-type thermoelectric member 200, which is opposite to the first end face, by solder or the like.

[0087] When the thermoelectric conversion element 500 is installed in an environment where electrode 540 is at a high temperature and electrode 550 is at a lower temperature than electrode 540, and electrodes 540 and 550 are connected to an external electric field circuit, a voltage is generated due to the Seebeck effect, and a current flows in the direction of electrode 550, the n-type thermoelectric conversion member 200, and electrode 540, as shown by the arrows in Figure 5. In detail, electrons in the n-type thermoelectric conversion layer 110 gain thermal energy from the high-temperature electrode 540 and move to the low-temperature electrode 550, releasing thermal energy, thereby generating a current in the n-type thermoelectric conversion layer 110.

[0088] In the thermoelectric conversion element 500, low contact resistance can be achieved between the n-type thermoelectric conversion member 200 and the electrode 540, and between the n-type thermoelectric conversion member 200 and 550, thereby providing a thermoelectric conversion element with an improved power factor. Furthermore, at the operating temperature, Mg ３ Sb ２ Since the diffusion of Mg from the thermoelectric material is suppressed, a stable and high thermoelectric conversion efficiency can be achieved over a long period of time.

[0089] In Figure 5, an example is shown in which an n-type thermoelectric conversion member 200 is used as the thermoelectric conversion element 500. However, instead of the n-type thermoelectric conversion member 200, the n-type thermoelectric conversion member 100 shown in Figure 1B may be used.

[0090] Figure 6 is a schematic diagram showing a π-type thermoelectric conversion element 600.

[0091] As shown in Figure 6, the thermoelectric conversion element 600 includes p-type thermoelectric conversion members 630 that are alternately connected in series with n-type thermoelectric conversion members 200. The n-type thermoelectric conversion members 200 and the p-type thermoelectric conversion members 630 are electrically connected in series with a low-temperature electrode 650 and a high-temperature electrode 640 in between. The p-type thermoelectric conversion member 630 includes a p-type thermoelectric conversion layer 610 made of p-type thermoelectric material, and metal layers (metallization layers) 620 are formed at both ends of the p-type thermoelectric conversion layer 610, and has a three-layer laminated structure similar to the n-type thermoelectric conversion member 100 (see Figure 1B).

[0092] The p-type thermoelectric material constituting the p-type thermoelectric conversion layer 610 is not particularly limited, but it preferably has high thermoelectric performance (for example, a ZT value of 0.4 to 1.6) at 600 K or lower, particularly near room temperature. Exemplarily, the p-type thermoelectric material may be a MgAgSb-based, BiTeSe-based, GeTe-based, AgSbTe ２ -based, CdSb-based, and CoSb ３ -based, etc.

[0093] An exemplary composition of the MgAgSb-based is Mg ０．９９ Cu ０．０１ Ag ０．９７ Sb ０．９９ . An exemplary composition of the BiTeSe-based is (Sb ０．７５ Bi ０．２５ ) ２ (Te ０．９７ Se ０．０３ ) ３ . An exemplary composition of the GeTe-based is Ge ０．８３ In ０．０１ Ti ０．０２ Sb ０．０９ Te. An exemplary composition of the CdSb-based is Cd ０．９９ Ag ０．０１ Sb. An exemplary composition of the CoSb ３ -based is Ce ０．９ Fe ３ CoSb １２ . These are just examples, and each composition ratio is not particularly limited.

[0094] The metal layer 620 is a layer that reduces the contact resistance between the p-type thermoelectric conversion member 630 and the electrodes 640 and 650. As the material of the metal layer 620, for example, Ag, Mg, Cu, and / or Sb may be used, but other materials may also be used.

[0095] A preferred example of the p-type thermoelectric conversion member 630 is one having Mg ｂ－ｅ B ｅ Ag ｃ Sb ｄIt is preferable to use an Sb layer as the metal layer 620. B is one element selected from the group consisting of copper (Cu), iron (Fe), zinc (Zn), ytterbium (Yb), and calcium (Ca). The parameters b, c, d, and e are preferably 0.95 ≤ b ≤ 1.05, 0.95 ≤ c ≤ 1.05, 0.95 ≤ d ≤ 1.05, and 0 ≤ e ≤ 0.1. Furthermore, when the metal layer 620 is an Sb layer, at least one element selected from the group consisting of Mg, Cu, and Bi may be added to the Sb layer.

[0096] By using such a p-type thermoelectric conversion element 630, it is possible to provide a thermoelectric conversion element with an improved power factor, particularly near room temperature.

[0097] Electrodes 640 and 650 can be made of general electrode materials, such as Fe, Ag, Al, Ni, Cu, etc.

[0098] As shown in Figure 6, when the thermoelectric conversion element 600 is installed in an environment where electrode 640 is at a high temperature and electrode 650 is at a lower temperature than electrode 640, and electrodes 640 and 650 are connected to an external electrical circuit, a voltage is generated due to the Seebeck effect, and current flows in the direction of electrode 650, n-type thermoelectric conversion member 200, electrode 640, and p-type thermoelectric conversion member 630, as indicated by the arrows in Figure 6.

[0099] Although Figure 6 shows an example of a π-type thermoelectric conversion element, a U-shaped thermoelectric power generation element (not shown) may also be used as the thermoelectric conversion element in this embodiment. In this case as well, the n-type thermoelectric conversion member 200 and the p-type thermoelectric conversion member 630 are connected alternately in series.

[0100] Thus, since the thermoelectric conversion element 600 uses the n-type thermoelectric conversion member 200 described above, low contact resistance can be achieved between it and the electrodes 640 and 650. Furthermore, since the diffusion of Mg can be suppressed in the power generation environment, low contact resistance can be maintained and high thermoelectric conversion efficiency can be maintained even under long-term power generation conditions.

[0101] Next, specific examples will be shown, but the present invention is not limited to these examples. [Examples 1 to 5: Thermoelectric conversion members] In general terms, in Examples 1 to 5, first, Mg ３ Sb ２ As an n-type thermoelectric material in the system, Mg ３．２ Sb ０．５９５ Bi １．４ Te ０．００５ In ０．０２ A sintered body was prepared. Next, using this sintered body, a laminate of a thermoelectric conversion member having a five-layer structure of Ni layer / Mg layer / sintered body of n-type thermoelectric material / Mg layer / Ni layer was formed, and the laminate was sintered to produce a thermoelectric conversion member. The manufacturing conditions are shown in Table 1. Details are explained below in [1] to [5]. Note that in Table 1, "-" indicates that measurement was not taken.

[0102]

[0103] [1] The raw materials used were Mg (powder, 99.99% purity, manufactured by Sigma-Aldrich Japan LLC), Sb (powder, 99.99% purity, manufactured by Sigma-Aldrich Japan LLC), Bi (powder, 99.99% purity, manufactured by Sigma-Aldrich Japan LLC), Te (powder, 99.99% purity, manufactured by Sigma-Aldrich Japan LLC), In (powder, 99.99% purity, manufactured by Sigma-Aldrich Japan LLC), and Ni (powder, 99.99% purity, manufactured by Sigma-Aldrich Japan LLC).

[0104] [2] As shown in the sintering table 1 of the n-type thermoelectric conversion layer, in Examples 1 to 5, Mg ３ Sb ２ As an n-type thermoelectric material in the system, Mg ３．２ Sb ０．５９５ Bi １．４ Te ０．００５ In ０．０２ A sintered body was fabricated using the above compositional formula Mg ａ Sb ２－ｂ－ｃ Bi ｂ M ｃ Z dIn this example, M=Te, Z=In, a=3.2, 2-b-c=0.595, b=1.4, c=0.005, and d=0.02. The raw materials from [1] above were weighed and mixed to satisfy this composition ratio to obtain a raw material mixture for the n-type thermoelectric material. Next, the raw material mixture for the n-type thermoelectric material (not shown) was placed on the upper surface of a punch 440 (Figure 4) fitted into a carbon die 460 (see Figure 4), and the punch 450 (Figure 4) was inserted. After that, pressure molding was performed by discharge plasma sintering (SPS, manufactured by Fuji Denpa Koki Co., Ltd., Doctor Lab Series 322La). In all examples (Examples 1 to 5), the heating and pressing conditions for SPS were a temperature of 973K, a pressure of 60MPa, and a sintering time of 10 minutes.

[0105] [3] Sintering of the Mg Layer Next, as shown in Figure 4, the raw material 430 for the Ni layer (metal layer), the raw material 420 for the Mg layer, and the sintered body 410 of the n-type thermoelectric conversion layer obtained in [2] were sequentially stacked on the upper surface of the punch 440 fitted into the die 460, and then the raw material 420 for the Mg layer and the raw material 430 for the Ni layer were stacked again in sequence. When adding the raw material for each layer, the surface of the added raw material was smoothed before adding the raw material for the next layer. After all the raw materials were stacked, the upper punch 450 was fitted in. Then, pressure molding was performed by discharge plasma sintering (SPS, manufactured by Fuji Denpa Koki Co., Ltd., Doctor Lab Series 322La). The sintering conditions for SPS in all examples (Examples 1 to 5) were a temperature of 773 K, a pressure of 60 MPa, and a sintering time of 10 minutes. The obtained samples are referred to as the thermoelectric conversion members of Examples 1 to 5, respectively.

[0106] [4] Annealing of Thermoelectric Conversion Members Next, the thermoelectric conversion members of Examples 1 to 5 were each subjected to annealing treatment under the conditions shown in Table 1. The annealing treatment was carried out in a vacuum (5 Pa) using a commercially available muffle furnace. Specifically, the sintered samples were removed from the SPS sintering furnace and placed in this muffle furnace for annealing. The temperature in the annealing conditions in Table 1 was set to 573 K, which can be considered to be around the actual operating temperature of the thermoelectric conversion element. This allowed for a simulated evaluation of the diffusion behavior of Mg and the thermoelectric characteristics when the thermoelectric conversion member is placed in a long-term power generation environment.

[0107] Furthermore, for the thermoelectric conversion component in Example 1, even if the cooling time after SPS is considered as annealing, it is less than 30 minutes, so it can be considered as not annealed (i.e., approximately as-annealed).

[0108] [5] Structural observation and compositional analysis of the interface of the thermoelectric conversion members in Examples 1 to 5 was observed using a scanning electron microscope (SEM, Hitachi, Ltd., model SU8000). In addition, the compositional analysis of the area near the interface between the n-type thermoelectric conversion layer and the Mg layer was performed using energy-dispersive X-ray spectroscopy (EDX) attached to the SEM. These results are shown in Figures 7 to 16 and Table 1 above.

[0109] Figure 7 is an SEM image showing the interface of the thermoelectric conversion member in Example 1. Figure 8 is a diagram showing the EDX mapping of Mg in Figure 7. Figure 9 is a diagram showing the EDX mapping of Sb in Figure 7. Figure 10 is a diagram showing the EDX mapping of Bi in Figure 7. Figure 11 is a diagram showing the EDX mapping of Ni in Figure 7. Figure 12 is an SEM image showing the interface of the thermoelectric conversion member in Example 5. Figure 13 is a diagram showing the EDX mapping of Mg in Figure 12. Figure 14 is a diagram showing the EDX mapping of Sb in Figure 12. Figure 15 is a diagram showing the EDX mapping of Bi in Figure 12. Figure 16 is a diagram showing the EDX mapping of Ni in Figure 12.

[0110] Note that Figures 8 to 11 and 13 to 16 are shown in grayscale, but the brightly lit areas indicate the presence of each element. As shown in Figures 7 to 11, the Ni layer / Mg layer / Mg of the thermoelectric conversion member in Example 1 ３ Sb ２ Each interface of the thermoelectric material system formed a good and clear bonding interface, and it was confirmed that no cracks or delaminations occurred. The thickness of the Mg layer was approximately 5 μm. Although not shown in the figures, similarly, the thermoelectric conversion members of Examples 2 to 4 also had Ni layer / Mg layer / Mg ３ Sb ２Each interface of the thermoelectric material system showed good and clear bonding interfaces, and it was confirmed that no cracks or delaminations occurred. Furthermore, no deposition layer formation was observed at the interfaces of each layer. Here, a good and clear bonding interface may mean a state in which the layer structure can be clearly identified visually, mainly based on SEM observation and elemental distribution images (EDS mapping), and a continuous bonding state can be confirmed along the interface. For example, Ni layer, Mg layer, and Mg ３ Sb ２ This may mean that each layer of the thermoelectric material is clearly distinguishable, no significant voids, cracks, or delamination are observed at the interface, and the layers are in continuous contact. Here, cracks may refer to cases where void-like defects that disrupt interlayer contact are observed near the interface in SEM observation. Delamination may refer to a state in which it is confirmed by SEM observation and elemental distribution images that the layers are not in continuous contact along the interface. Such a determination does not have to be based on specific magnification or numerical dimensional conditions. It may be based on whether the layer structure and interface state can be confirmed stably and reproducibly by normal SEM observation.

[0111] Therefore, according to the manufacturing method of this embodiment described above, Mg ３ Sb ２ It was confirmed that a thermoelectric conversion member can be provided in which an n-type thermoelectric conversion layer made of a thermoelectric material, an Mg layer, and a Ni layer are integrally molded, and that good bonding interfaces can be obtained between each layer.

[0112] As shown in Figures 12 to 16, even in the thermoelectric conversion member of Example 5 after long-term annealing treatment, Mg ３ Sb ２ The interface between the thermoelectric material and the Mg layer maintained a good and clear bonding interface, and no cracks or delamination were observed.

[0113] Furthermore, as shown in Figures 13 to 16, the Mg layer remained very stable even after long-term annealing, exhibiting high thermal stability at the annealing temperature (573 K). Also, as shown in Figure 13, Mg ３ Sb ２No diffusion of Mg elements from the thermoelectric material into the Ni metal layer was observed.

[0114] The thickness of the Mg layer was measured by observing the cross-section of the obtained thermoelectric conversion member with an electron microscope and based on the SEM image and elemental distribution image (EDS mapping). Measurements were taken at multiple randomly selected locations in areas where the Mg layer could be clearly identified in the SEM image, etc. For example, this might mean areas where the Mg layer can be distinguished from other layers with sufficient contrast in the SEM image, and where the boundary (or interface) where the Mg concentration distribution changes abruptly in the EDS mapping substantially coincides with the boundary (or interface) of the Mg layer in the SEM image. The distance between such boundaries (or interfaces) was measured as the thickness, and the thickness was evaluated by the arithmetic mean of these measurements. Specifically, the thickness was measured at five randomly selected points along the interface, and the arithmetic mean was taken as the thickness of the Mg layer. The SEM images shown in Figures 8 and 13 show the observation results for Example 1 and Example 5, respectively. Due to differences in observation positions, there may be positional (or spatial) variations in the local thickness of the Mg layer. Therefore, even if the thickness of the Mg layer appears visually slightly larger in Figure 13, this is thought to reflect local differences due to differences in observation positions. It is not considered to indicate that the Mg layer expanded or thickened at different locations on the interface due to the annealing treatment. As a result of evaluation using the above measurement method, the average thickness of the Mg layer was approximately 5 μm in all samples. No significant decrease in the average thickness of the Mg layer was observed due to the long annealing time. In other words, no signs of significant wear or thinning of the Mg layer were observed, and it was judged that the function as a barrier layer was maintained. From this, it is considered that the Mg layer according to the present invention can function as a substantially stable barrier layer even when long-term use is assumed. In particular, comparing Example 1 (see Figure 8) and Example 5 (see Figure 13), no significant decrease in the average thickness of the Mg layer was observed before and after long-term annealing, and it was confirmed that the Mg layer maintained high thermal stability in the environment. In other words, the n-type thermoelectric conversion member of this embodiment can be used stably for a long period of time in a high-temperature environment close to the actual power generation temperature of 573 K.

[0115] Figures 17A and 17C show the Mg of Example 1 and Example 5. ３ Sb ２ This is an EDX line scan of Mg, Sb, Bi, and Ni in a thermoelectric material system / Mg layer / Ni layer. The EDX line scan is Mg ３ Sb ２ This is the result of a one-dimensional scan in the normal direction from the thermoelectric material side through the Mg layer to the Ni layer.

[0116] Figure 17A shows the EDX line scan of the thermoelectric conversion member of Example 1. In Figure 17A, the gray shaded area indicates the region of the Mg layer, which is the barrier layer. The gray shaded area in the figure indicates the section on the line where the signal for the element Mg was clearly detected, and the length of this section reflects the local thickness of the Mg layer at the measurement location. Figure 17B shows the SEM image and the graph obtained from the EDX line scan side by side. This EDX line scan allows for evaluation of the layer thickness in the normal direction at a specific location. It is not an average thickness that takes into account the thickness distribution in the length direction along the interface. The region on the left side of the figure of the Mg layer is Mg ３ Sb ２ This is the region of the n-type thermoelectric conversion layer made of a thermoelectric material, and the region on the right side of the Mg layer in the figure is the region of the Ni layer, which is a metal layer. As shown in Figure 17A, Mg ３ Sb ２ It can be confirmed that a high-concentration Mg barrier was formed by creating an Mg layer on the end face of the thermoelectric material.

[0117] Furthermore, in Figure 17A, as shown in Figures 7 to 11, the thermoelectric conversion member of Example 1 is Mg ３ Sb ２ It can be seen that the regions of the thermoelectric material system, the Mg layer, and the Ni layer are clearly separated and formed. In other words, even after the SPS sintering process at 773K, the Mg in the Mg layer has not thermally diffused to other adjacent regions. Similarly, it can be seen that the constituent elements of each region have not thermally diffused to other adjacent regions. From this, it can be said that the SPS sintering conditions were appropriate and a high-quality thermoelectric conversion component was manufactured.

[0118] Figure 17C shows the EDX line scan of the thermoelectric conversion member of Example 5. As shown in Figure 17C, after a long-term annealing treatment at 573K for 30 days, Mg ３ Sb ２ No diffusion of Mg from the thermoelectric material (left side of the figure) into the Ni layer (right side of the figure) was observed. Furthermore, as is clear from comparing the gray shaded areas in both Figures 17A and 17C, there was virtually no change in the thickness of the Mg layer before and after annealing. The actual size equivalent of the section where the Mg signal was detected was approximately 5 μm in both cases, which may be considered almost the same within the range of measurement error. It is possible that the drawings attached to this application may have different scales. Generally, a measurement error of ±5% of the measured value is often estimated. A slightly wider margin of error, such as ±10% of the measured value, might be acceptable.

[0119] This demonstrated that even after a long annealing period of 30 days, the Mg element in the thermoelectric material could not diffuse across the Mg barrier layer to the Ni layer.

[0120] That is, Mg ３ Sb ２ By forming an Mg layer on the end face of the thermoelectric material, a high-concentration Mg barrier is created, allowing for long-term power generation environments to maintain Mg ３ Sb ２ We were able to demonstrate that the diffusion and departure of Mg from the thermoelectric material can be suppressed.

[0121] [6] Contact Resistivity The contact resistivity of the thermoelectric conversion materials in Examples 1 to 5 was measured using a biaxial resistance distribution measuring device (S1331, manufactured by Mottainai Energy Co., Ltd.). These results are shown in Figures 18 to 19 and in Table 1 above.

[0122] Figure 18 shows the contact resistivity ρ in the thermoelectric conversion members of Examples 1 to 5. ｃ This figure shows the annealing time dependence of the contact resistivity ρ. ｃ Mg ３ Sb ２ This is the contact resistivity at the interface between the thermoelectric material and the Mg layer.

[0123] As shown in Table 1 and Figure 18, even with increasing annealing time at 573K, the contact resistivity ρ remains the same throughout Examples 1 to 5. ｃ All values ​​are 10 μΩcm ２ The value remained below a certain level and no significant increase in resistance was observed. Furthermore, in Example 5, even after annealing at 573K for 30 days, the contact resistivity ρ ｃ It is 4.18 μΩcm ２ It remained at this level, and it was confirmed that low contact resistance could be maintained even after long-term heat treatment.

[0124] From this, Mg ３ Sb ２ In a thermoelectric conversion element using a thermoelectric material, it was demonstrated that the Mg layer functions as an excellent metal layer and diffusion barrier layer capable of maintaining low contact resistance.

[0125] Figure 19 shows the Mg layer / Mg in Examples 1 to 5. ３ Sb ２ This is the position dependence of the resistance value of a thermoelectric material.

[0126] In Figure 19, the gray-shaded area represents a region where Ni layers and Mg layers are stacked from left to right. Since both of these layers are metals, their electrical resistance is very low and no position dependence is observed. The area to the right of the gray-shaded area is Mg ３ Sb ２ This is a region of an n-type thermoelectric conversion layer made of a thermoelectric material. It was confirmed that the resistance of the n-type thermoelectric conversion layer increases linearly with increasing distance from the Mg layer / n-type thermoelectric conversion layer interface, but does not show a significant change with increasing annealing time.

[0127] In addition, as shown in Table 1, Mg is present in all of Examples 1 to 5. ３ Sb ２ The conductivity of thermoelectric materials is approximately 9 × 10⁻⁶. ４ Sm －１ It was confirmed that the degree and high value could be maintained. Under the condition of no annealing in Example 1, the conductivity of the thermoelectric material was 8.3 × 10⁻⁶. ４ Sm －１However, no decrease in conductivity was observed with increasing annealing time; on the contrary, a slight increase was confirmed. Furthermore, even after 30 days of annealing, the conductivity of the thermoelectric material in Example 5 was 8.6 × 10⁻⁶. ４ Sm －１ This showed a high value. This indicates that the performance of the thermoelectric material does not deteriorate even after high-temperature annealing. In other words, it indicates that the Mg layer effectively suppressed the diffusion of Mg in the thermoelectric material, resulting in the high maintenance of the thermoelectric material's properties.

[0128] [Examples 6-7: Thermoelectric Conversion Elements] Using the thermoelectric conversion members of Example 1 and Example 5, thermoelectric conversion elements shown in Figures 20A and 20B were manufactured and their thermoelectric conversion characteristics were evaluated (Examples 6 and 7).

[0129] Figure 20A is a top view of a π-type two-pair thermoelectric conversion element 700 using the thermoelectric conversion members of Example 1 and Example 5, and Figure 20B is a cross-sectional view along the line I-I.

[0130] In Examples 6 and 7, as shown in Figure 20A, a thermoelectric conversion element 700 was fabricated containing two pairs of n-type thermoelectric conversion members 200 and p-type thermoelectric conversion members 630, and the thermoelectric conversion efficiency was evaluated.

[0131] First, as preparation for the elements, two rectangular parallelepipeds measuring approximately 3.8 mm × 3.8 mm × 6 mm were cut from the n-type thermoelectric conversion members of Example 1 or Example 5, to produce a total of four n-type thermoelectric conversion members 200 (Example 6 or Example 7). On the other hand, for the p-type thermoelectric conversion member 630, MgAgSb was used as the p-type thermoelectric conversion layer 610 (see Figure 6), and MgCuSb was used as the metal layer 620 (see Figure 6). A three-layer structure of MgCuSb layer / MgAgSb thermoelectric material / MgCuSb layer was formed, and four p-type thermoelectric conversion members 630 of approximately the same size as the n-type thermoelectric conversion member 200 were produced.

[0132] The components fabricated in this manner were connected in series in the following order, as shown in Figures 20A and 20B or Figure 6: electrode 650 / n-type thermoelectric conversion member 200 of Example 1 or Example 5 / electrode 640 / p-type thermoelectric conversion member 630 / electrode 650 / n-type thermoelectric conversion member 200 of Example 1 or Example 5 / electrode 640 / p-type thermoelectric conversion member 630 / electrode 650, to fabricate two π-type 2-pair thermoelectric conversion elements 700 (Example 6 or Example 7).

[0133] The thermoelectric conversion efficiency of the thermoelectric conversion elements in Example 6 and Example 7 was measured using a Mini-PEM (manufactured by ADVANCE RIKO). The temperature on the low-temperature side was maintained at 293 K, and the temperature on the high-temperature side was varied from 373 K to 593 K, thereby varying the temperature difference between the electrodes from 78 K to 300 K, and measurements were taken under vacuum conditions (5 Pa). The results for Example 6 and Example 7 are shown in Figures 21 and 22, respectively.

[0134] Figure 21 is a graph showing the thermoelectric conversion efficiency η of a π-type two-pair thermoelectric conversion element (Example 6) using the thermoelectric conversion member of Example 1.

[0135] As shown in Figure 21, a maximum conversion efficiency of 8.1% was obtained at a temperature difference of 294 K, and the thermoelectric conversion element using the thermoelectric conversion material of Example 1 showed a sufficiently high thermoelectric conversion efficiency. As a result, the Mg layer was Mg ３ Sb ２ We were able to demonstrate that good electrical bonding was achieved with the thermoelectric material, keeping the contact resistivity low and consequently improving the thermoelectric conversion efficiency.

[0136] Figure 22 is a graph showing the thermoelectric conversion efficiency η of a π-type two-pair thermoelectric conversion element (Example 7) using the thermoelectric conversion member of Example 5.

[0137] As shown in Figure 22, the thermoelectric conversion efficiency η of the thermoelectric conversion element in Example 7, using the thermoelectric conversion member of Example 5 after 30 days of annealing, reached a maximum conversion efficiency of approximately 8.2% at a temperature difference of 275 K, maintaining a high efficiency comparable to that of the unannealed thermoelectric conversion efficiency of Example 6 shown in Figure 21. This demonstrates that the Mg layer effectively functions as an Mg diffusion barrier layer, effectively suppressing the increase in contact resistance and the decrease in thermoelectric performance, even after prolonged high-temperature conditions, and keeping the thermoelectric conversion element in a chemically stable state.

[0138] Thus, the Mg layer is Mg ３ Sb ２ It was demonstrated that it functions as an excellent Mg diffusion barrier layer for thermoelectric materials, maintaining low contact resistance and high thermoelectric conversion efficiency even after a long 30-day annealing period. According to this embodiment, the conventional problem of Mg ３ Sb ２ We were able to demonstrate that we can overcome the problem of reduced thermoelectric performance due to the diffusion of Mg from the thermoelectric material.

[0139] The thermoelectric material according to this embodiment can be used in power generation devices and thermoelectric cooling devices, particularly those used at or near room temperature. It is also useful as an IoT standalone power source.

[0140] 100, 200 n-type thermoelectric conversion component 110 n-type thermoelectric conversion layer 120 Mg layer 130 Metal layer (Ni layer) 410 n-type thermoelectric conversion layer 420 Raw material for Mg layer 430 Raw material for Ni layer 440, 450 Punch 460 Die 500, 600, 700 Thermoelectric conversion element 540, 550, 640, 650 Electrode 610 p-type thermoelectric conversion layer 620 Metal layer 630 p-type thermoelectric conversion component

Claims

1. A thermoelectric conversion member comprising a thermoelectric conversion layer made of an n-type thermoelectric material containing at least magnesium (Mg) and antimony (Sb) and / or bismuth (Bi), and an Mg layer located on at least one end face side of the thermoelectric conversion layer.

2. The n-type thermoelectric material is Mg ａ Sb ２－ｂ－ｃ Bi ｂ M ｃ Z d The thermoelectric conversion member according to claim 1, comprising an inorganic compound represented by , where M is selenium (Se) and / or tellurium (Te), Z is at least one element selected from the group consisting of indium (In), molybdenum (Mo), copper (Cu), cobalt (Co), and manganese (Mn), and parameters a, b, c, and d satisfying 3 ≤ a ≤ 3.5, 0 ≤ b ≤ 2, 0 ≤ c ≤ 0.1, and 0 ≤ d ≤ 0.

1.

3. The thermoelectric conversion member according to claim 1 or 2, wherein the thickness of the Mg layer is 1 μm or more and 1000 μm or less.

4. The thermoelectric conversion member according to any one of claims 1 to 3, wherein the thermoelectric conversion layer and the Mg layer are sintered bodies.

5. The Mg layer is P6 ３ A thermoelectric conversion member according to any one of claims 1 to 4, belonging to the space group / mmc.

6. The thermoelectric conversion member according to any one of claims 1 to 5, wherein the Mg layer is located on both end faces of the thermoelectric conversion member.

7. The thermoelectric conversion member according to any one of claims 1 to 6, further comprising a metal layer on the end face side of the Mg layer that is not in contact with the n-type thermoelectric conversion layer.

8. The thermoelectric conversion member according to claim 7, wherein the metal layer is made of a Ni layer.

9. The thermoelectric conversion member according to any one of claims 1 to 8, wherein the Mg layer further comprises at least one element selected from the group consisting of iron (Fe), niobium (Nb), and molybdenum (Mo).

10. The thermoelectric conversion member according to claim 9, wherein the content of the element added to the Mg layer is less than 10 at%.

11. A method for manufacturing a thermoelectric conversion member according to any one of claims 1 to 10, comprising forming a laminate of a thermoelectric conversion layer made of an n-type thermoelectric material comprising at least magnesium (Mg) and antimony (Sb) and / or bismuth (Bi), and a raw material containing Mg as a raw material for the Mg layer, and sintering the laminate.

12. The method according to claim 11, wherein the sintering includes discharge plasma sintering.

13. The method according to claim 12, wherein the sintering includes sintering the laminate at a temperature range of 673 K to 973 K and a pressure range of 40 MPa to 80 MPa.

14. The method according to claim 13, wherein the sintering includes sintering the laminate at a temperature range of 723 K to 823 K, at a pressure range of 50 MPa to 70 MPa, for a time of 5 minutes to 20 minutes.

15. The method according to claim 14, wherein the sintering includes sintering the laminate at 773 K and 60 MPa for 10 minutes.

16. A method for manufacturing a thermoelectric conversion member according to any one of claims 1 to 10, comprising forming an Mg layer on at least one end face side of a thermoelectric conversion layer made of an n-type thermoelectric material comprising at least magnesium (Mg) and antimony (Sb) and / or bismuth (Bi) by at least one method selected from the group consisting of physical vapor deposition, chemical plating, and electroplating.

17. The method according to claim 16, wherein the Mg layer is formed by magnetron sputtering.

18. A thermoelectric power generation element comprising at least one n-type thermoelectric conversion member, wherein the n-type thermoelectric conversion member is the thermoelectric conversion member described in any one of claims 1 to 10.

19. The thermoelectric element according to claim 18, further comprising p-type thermoelectric members alternately connected in series with the n-type thermoelectric members.

20. The p-type thermoelectric conversion member is MgAgSb-based, BiTeSe-based, GeTe-based, AgSbTe ２ CdSb system, CdSb system, and CoSb ３ A thermoelectric conversion element according to claim 19, comprising a p-type thermoelectric material selected from the group consisting of systems.

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