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

Abstract

The present invention provides: a thermoelectric conversion member that makes it possible to reduce contact resistance between a MgAgSb-based thermoelectric material and an electrode; a production method for the same; and a thermoelectric conversion element.　A thermoelectric conversion member according to the present invention comprises at least: a thermoelectric conversion layer which comprises a p-type thermoelectric material that includes magnesium (Mg), silver (Ag), and antimony (Sb); and an Sb layer which is positioned on at least one end surface of the thermoelectric conversion layer. A production method for a thermoelectric conversion member according to the present invention comprises at least: forming a laminate of a raw material that includes Sb as a raw material for an Sb layer, and a p-type thermoelectric material or a raw material mixture for a p-type thermoelectric material that is obtained by mixing a raw material containing magnesium (Mg), a raw material containing silver (Ag), and a raw material containing antimony (Sb); 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] Thermoelectric conversion, which can directly convert heat into electricity without emitting greenhouse gases, is highly anticipated as a power generation device that can recover waste heat. Furthermore, thermoelectric elements are also expected to serve as independent power sources for IoT devices, and improving thermoelectric conversion efficiency near room temperature is widely desired as a technology that will support the rapid development of the IoT society.

[0003] In recent years, magnesium-silver-antimony (MgAgSb) materials have attracted attention as p-type thermoelectric materials that exhibit high thermoelectric conversion efficiency near room temperature (see Patent Document 1). However, when incorporating MgAgSb materials into thermoelectric conversion elements, techniques for reducing contact resistance between the material and electrodes are still under development, and there is a need for a technique that can maintain low contact resistance over a long period of time.

[0004] Non-patent document 1 describes the fabrication of a thermoelectric conversion element in which an MgAgSb-based thermoelectric material is sandwiched between silver (Ag) metallization layers (metal layers), with a resistance of 9.1 μΩcm. ２ It has been disclosed that an average contact resistance of 8.6% and a conversion efficiency of 8.6% were achieved. However, in a thermoelectric conversion element in which an MgAgSb-based thermoelectric material is sandwiched between Ag metallization layers, the contact resistance was 1000 μΩcm after 12 hours of annealing. ２ The increase is so significant that it exceeds a certain level, resulting in a drastic decrease in performance (see Non-Patent Document 2).

[0005] In contrast, Non-Patent Document 2 describes the fabrication of a thermoelectric conversion element in which an MgAgSb-based thermoelectric material is sandwiched between MgCuSb metallization layers instead of Ag, and the contact resistance remains at 1 μΩcm even after 16 days of annealing. ２The following disclosures show that the levels could be kept low. However, with this combination, the magnesium (Mg) contained in the MgSb material is unsuitable for brazing and plating, making the bonding between the MgSb material and the metal electrode a challenge. In addition, since the properties of MgAgSb thermoelectric materials change at high temperatures above 400°C, high-melting-point solders cannot be used.

[0006] Patent Document 2 discloses a method of forming an electrode bonding layer (metal layer) of about 100 to 200 μm thick by thermal spraying a metal (copper, nickel, molybdenum, etc.) onto an MgAgSb-based thermoelectric material. However, a simpler and lower-cost method is desired.

[0007] Thus, in conventional MgAgSb-based thermoelectric materials that exhibit highly efficient power generation characteristics near room temperature, there is a need for a technology that can reduce the contact resistance between the thermoelectric material and the electrode.

[0008] International Publication No. 2022 / 059443, Patent No. 7562115

[0009] Zihang Liu, et al. , “High thermoelectric performance of a-MgAgSb for power generation”, Energy Environmental Science, 11, 23, 2018. Liangjun Xie, et al. , “Screening strategy for developing thermoelectric interface materials”, Science, 382, ​​921-928, 2023.

[0010] Based on the above, the objective in the embodiments of the present invention is to provide a thermoelectric conversion member that can reduce the resistance between the MgAgSb-based thermoelectric material and the electrode, a method for manufacturing the same, and a thermoelectric conversion element.

[0011] In an embodiment of the present invention, the thermoelectric conversion member may include at least a thermoelectric conversion layer made of a p-type thermoelectric material containing magnesium (Mg), silver (Ag), and antimony (Sb), and an Sb layer located on at least one end surface of the thermoelectric conversion layer, so as to solve the above problems. In any of the above thermoelectric conversion members, the Sb layer may further contain at least one additive element selected from the group consisting of magnesium (Mg), copper (Cu), and bismuth (Bi). In any of the above thermoelectric conversion members, the content of the additive element added to the Sb layer may be 0.1 at% or more and 10 at% or less. In any of the above thermoelectric conversion members, the thickness of the Sb layer may be 50 μm or more and 1000 μm or less. In any of the above thermoelectric conversion members, the p-type thermoelectric material is Mg ｂ Ag ｃ Sb ｄ , Mg ｂ－ｅ B ｅ Ag ｃ Sb ｄ , Mg ｂ Ag ｃ Sb ｄ + fwt% Z, and Mg ｂ－ｅ B ｅ Ag ｃ Sb ｄ + fwt% Z may be one or more compounds selected from the group consisting of. In any of the above thermoelectric conversion members, B may be one or more elements selected from the group consisting of copper (Cu), iron (Fe), zinc (Zn), ytterbium (Yb), and calcium (Ca). In any of the above thermoelectric conversion members, Z is stearic acid (C １８ H ３６ O ２ ), palmitic acid (C １６ H ３２ O ２ ), icosanoic acid (C ２０ H ４０ O ２ ), zinc stearate (C ３６ H ７０ ZnO ４ ), magnesium stearate (C ３６ H７０ MgO ４ ), barium stearate (C ３６ H ７０ BaO ４ ), calcium stearate (C ３６ H ７０ CaO ４ ), sodium stearate (C １８ H ３５ NaO ２ ), and N,N'-ethylenedi(stearamide)(C ３８ H ７６ N ２ O ２ ) may be one or more fatty acids selected from the group consisting of ). In any of the thermoelectric conversion members described above, the parameters b, c, d, e, and f may satisfy 0.95 ≤ b ≤ 1.05, 0.95 ≤ c ≤ 1.05, 0.95 ≤ d ≤ 1.05, 0 < e ≤ 0.1, and 0 < f ≤ 1.0. In any of the thermoelectric conversion members described above, the thermoelectric conversion layer and the Sb layer may be sintered bodies. In any of the thermoelectric conversion members described above, at least Mg may be present between the thermoelectric conversion layer and the Sb layer. ３ Sb ２The thermoelectric conversion member may further have a precipitate layer containing the above. In any of the thermoelectric conversion members described above, the thickness of the precipitate layer may be in the range of 1 μm to 50 μm. In any of the thermoelectric conversion members described above, the Sb layer may contain a substance belonging to the R-3m space group. In any of the thermoelectric conversion members described above, the Sb layer may be located on both ends of the thermoelectric conversion layer. In embodiments of the present invention, the method for manufacturing the thermoelectric conversion member may include at least mixing a raw material containing magnesium (Mg), a raw material containing silver (Ag), and a raw material containing antimony (Sb) to form a raw material mixture for the p-type thermoelectric material, or forming a laminate of the p-type thermoelectric material and a raw material containing Sb as a raw material for the Sb layer, and in the method for manufacturing the thermoelectric conversion member described above, sintering the laminate. The above problems are solved. In the method for manufacturing the thermoelectric conversion member described above, the sintering may be performed by discharge plasma sintering. In any of the above-described methods for manufacturing a thermoelectric conversion member, the sintering may be performed by sintering the laminate at a temperature range of 500K to 600K and a pressure range of 50MPa to 70MPa. In any of the above-described methods for manufacturing a thermoelectric conversion member, the sintered body obtained by the sintering may further include annealing it in the atmosphere. In any of the above-described methods for manufacturing a thermoelectric conversion member, the annealing may be performed by annealing the sintered body at a temperature range of 500K to 600K for a period of 30 minutes to 50 days. In an embodiment of the present invention, the method for manufacturing a thermoelectric conversion member may include forming an Sb layer on at least one end face of a sintered body made of a p-type thermoelectric material containing at least magnesium (Mg), silver (Ag), and antimony (Sb) by one method selected from the group consisting of physical vapor deposition, chemical plating, and electroplating. The above problems are solved. In an embodiment of the present invention, the thermoelectric conversion element is a thermoelectric power generation element comprising at least a p-type thermoelectric conversion member, wherein the p-type thermoelectric conversion member may be any of the thermoelectric conversion members described above. The above problems are solved. In any of the thermoelectric conversion elements described above, an n-type thermoelectric conversion member may be provided, which is alternately connected in series with the p-type thermoelectric conversion member.In any of the thermoelectric conversion elements described above, the n-type thermoelectric conversion member is Mg. ２ Sb ３ system, BiTeSe system, CoSb ３ System, and Mg ２ It may include (Si,Sn)-based n-type thermoelectric materials. A layer for joining a thermoelectric element made of a p-type thermoelectric material containing at least magnesium (Mg), silver (Ag), and antimony (Sb) to an electrode, the layer containing 90 at% or more antimony (Sb). The joining layer further contains 0.1 at% to 10 at% of at least one selected from magnesium (Mg), copper (Cu), and bismuth (Bi), as described above. A method for forming a layer for joining a thermoelectric element made of a p-type thermoelectric material containing at least magnesium (Mg), silver (Ag), and antimony (Sb) to an electrode, comprising laminating a metal or metalloid containing 90 at% or more antimony (Sb) on the surface of the thermoelectric element, heating at a heating temperature of 500 K to 600 K, and applying a pressure of 50 MPa to 60 MPa to the thermoelectric element and the laminate on its surface.

[0012] In an embodiment of the present invention, the thermoelectric conversion member has an Sb layer provided on at least one end face of a thermoelectric conversion layer made of a p-type thermoelectric material. When electrodes are electrically connected to the p-type thermoelectric layer via the Sb layer, the electrode contact resistance can be reduced. Furthermore, in an embodiment of the present invention, using such a thermoelectric conversion member can reduce electrode contact resistance. A thermoelectric conversion element with high thermoelectric conversion efficiency can be provided.

[0013] In an embodiment of the present invention, the method for manufacturing the thermoelectric conversion member involves sintering a raw material mixture of p-type thermoelectric material or a laminate of p-type thermoelectric material and Sb layer raw material. The sintering process of the p-type thermoelectric material and the bonding of the p-type thermoelectric material and Sb layer can be carried out in the same process. This simplifies the manufacturing process and reduces manufacturing costs.

[0014] Schematic diagram showing a p-type thermoelectric conversion member according to this embodiment Schematic diagram showing a p-type thermoelectric conversion member according to this embodiment Schematic diagram showing a p-type thermoelectric conversion member according to this embodiment Diagram schematically showing an MgAgSb-based crystal having a characteristic structure of a half-Heusler compound Flowchart showing an exemplary manufacturing process of the thermoelectric conversion member according to this embodiment 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 of Example 1 Diagram showing the EDX mapping of Mg in Figure 6 Diagram showing the EDX mapping of Ag in Figure 6 Diagram showing the EDX mapping of Sb in Figure 6 SEM image showing the interface of the thermoelectric conversion member of Example 15 Diagram showing the EDX mapping of Mg in Figure 10 Figure 10 shows the EDX mapping of Ag, Figure 10 shows the EDX mapping of Sb, Figure 10 shows the EDX line scan of Mg, Ag, and Sb near the interface between the Sb layer of the thermoelectric conversion member in Example 1 and the MgAgSb-based thermoelectric material, Figure 15 shows the EDX line scan of Mg, Ag, and Sb near the interface between the Sb layer of the thermoelectric conversion member and the MgAgSb-based thermoelectric material, Figure 1 and Example 13 to Example 15 show the annealing time dependence of the contact resistivity of the thermoelectric conversion elements, Schematic diagram showing a thermoelectric conversion element, Graph showing the thermoelectric conversion efficiency η of a π-type 2-pair thermoelectric conversion element using the thermoelectric conversion member in Example 1, Graph showing the thermoelectric conversion efficiency η of a π-type 2-pair thermoelectric conversion element using the thermoelectric conversion member in Example 15

[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] <On the power generation efficiency of thermoelectric elements and the contact resistance of the metallization 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 metallization layer (sometimes called a metal layer, thermoelectric interface material TeiM (Thermoelectric Interface Material), or intermediate layer) between the thermoelectric material and the electrode. The metallization 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 "metallization layer / thermoelectric material / metallization layer," in which the thermoelectric material is sandwiched between two metallization layers.

[0018] 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 metallization layer.

[0019] Therefore, one of the most important requirements for the metallization layer is a low contact resistivity ρ between it and the thermoelectric material. ｃ This results in the following: Furthermore, during long-term use at power generation temperatures, elemental interdiffusion may occur at the interface between the thermoelectric material and the metallization layer, potentially leading to a gradual decrease in the performance of the thermoelectric conversion element. Thus, there were also challenges associated with changes at the interface. In response to this, modification of the metallization layer material was desired in order to obtain a power generation device with high efficiency and stable output.

[0020] To date, silver (Ag) has been widely used as the material for the metallization layer when fabricating thermoelectric elements using MgAgSb-based thermoelectric materials. Ag has high electrical and thermal conductivity, and is soft and easy to process, making it a suitable material for obtaining low contact resistance temporarily.

[0021] However, the contact resistivity between the MgAgSb-based thermoelectric material and the Ag layer was 1000 μΩcm after annealing at 553 K for 12 hours. ２As a result, the power generation characteristics decrease significantly (see Non-Patent Document 1). This degradation is due to the diffusion of antimony (Sb) from the MgAgSb-based thermoelectric material to the Ag layer, and an increase in cracks at the interface.

[0022] To overcome this degradation, for example, Non-Patent Document 2 describes the fabrication of a thermoelectric conversion element using the intermetallic compound MgCuSb as the metallization layer, with a configuration of MgCuSb layer / MgAgSb-based thermoelectric material / MgCuSb layer. By using the Sb-containing compound MgCuSb as the metallization layer, the diffusion of Sb was suppressed. As a result, even after annealing at 553K for 16 days, the resistance remained at 1 μΩcm. ２ A low contact resistivity of less than 100% was maintained (see Non-Patent Document 2).

[0023] However, the manufacturing process for thermoelectric conversion elements containing MgCuSb layers / MgAgSb-based thermoelectric materials / MgCuSb layers is relatively complicated, and the solderability (wettability) is poor. Therefore, there has been a demand for a metallization layer that can achieve low contact resistance through a simpler process.

[0024] The inventors of this application searched for a more suitable material for the metallization layer in order to further improve the conversion efficiency of thermoelectric conversion elements of MgAgSb-based thermoelectric materials, and devised and demonstrated an antimony (Sb) metallization layer.

[0025] Antimony (Sb) has a high vapor pressure and easily evaporates during heating, making it unsuitable for coating by thermal spraying, as described in Patent Document 2, for example. Given this technical background, no one had previously conceived of using antimony as a metallization layer. In contrast, the present inventors, through trial and error, conceived of a thermoelectric material and its manufacturing method according to this embodiment, and confirmed the effects shown in the examples. That is, this embodiment provides a simpler and more efficient thermoelectric conversion element. Preferred embodiments are described below.

[0026] (First Embodiment) In the first embodiment, a thermoelectric conversion member and a method for manufacturing the same will be described.

[0027] <Thermoelectric Conversion Member> Figures 1A to 1C are schematic diagrams showing a p-type thermoelectric conversion member 100 according to this embodiment.

[0028] The p-type thermoelectric conversion member 100 according to this embodiment comprises a p-type thermoelectric conversion layer 110 and an Sb layer 120 located on at least one end face of the p-type thermoelectric conversion layer 110, as shown in Figures 1A to 1C. The p-type thermoelectric conversion layer 110 is made of a p-type thermoelectric material containing at least magnesium (Mg), silver (Ag), and antimony (Sb). In the specification of this application, with respect to a thermoelectric conversion layer, the end face may mean the upper or lower surface, or the front or back surface of the layer. For example, in Figure 1B, the p-type thermoelectric conversion member 100 is composed of a central p-type thermoelectric conversion layer 110 and Sb layers 120 arranged on its upper and lower surfaces (upper and lower surfaces) in the figure. In such a configuration in which each layer is stacked, the portion that constitutes the interface between the layers can be called the end face.

[0029] In this specification, a p-type thermoelectric material containing at least Mg, Ag, and Sb contains at least an inorganic compound containing Mg, Ag, and Sb, and is referred to as an MgAgSb-based thermoelectric material.

[0030] The MgAgSb crystals constituting the MgAgSb-based thermoelectric material preferably have a half-Heusler α-phase and belong to the I-4c2 space group (the 120th in the International Tables for Crystallography). Such a crystal structure is schematically shown in Figure 1D. In this specification, "-4" represents "4 with an overbar". As an example of an MgAgSb-based thermoelectric material, Mg １ Ag １ Sb １ Mg ０．９８ Ag １．０２ Sb １ Mg １ Ag １．０１ Sb １．０２ These are some examples. In addition, examples of MgAgSb-based thermoelectric materials include materials in which part of the Mg site is replaced and solid-solved with copper (Cu), iron (Fe), etc., and mixtures with fatty acids such as stearic acid.

[0031] The Sb layer 120 is a metallization layer (metal phase) containing Sb, which reduces the resistance between the p-type thermoelectric conversion layer 110 and the electrodes (for example, electrodes 150 and 160, which will be described later in Figure 4), and suppresses thermal diffusion of Sb from the p-type thermoelectric conversion layer 110 to the electrodes. (Here, resistance is, for example, the resistance between the p-type thermoelectric conversion layer 110 and the electrodes (for example, 150 and 160) when the p-type thermoelectric conversion layer 110 is in contact with the electrodes (for example, 150 and 160) via the Sb layer 120.) The metallization layer is sometimes called an electrode junction layer or thermoelectric element interface material (TeiM). Antimony (Sb) has a melting point of 903.78 K (630.63 °C), a boiling point of 1860 K (1587 °C), a rhombohedral crystal structure, and a space group of R-3m.

[0032] Preferably, the Sb layer 120 may be a layer of Sb alone. More preferably, the Sb layer 120 is a layer mainly composed of Sb. For example, Sb may be the main component among the components constituting the Sb layer 120. The Sb content may be 50 wt% or more. If the Sb layer 120 contains elements other than Sb, it is sufficient that the Sb content is the highest among the components of the layer. Other components other than Sb may be, for example, unavoidable impurities that may be contained in the raw materials. Furthermore, as will be described later, when the MgAgSb-based thermoelectric material and the Sb layer are formed as flexible layers, the Sb layer may be a mixture of a material mainly composed of Sb and an organic material.

[0033] As shown in Figure 1A, the Sb layer 120 may be formed on one end face of the p-type thermoelectric conversion layer 110, or as shown in Figure 1B, it may be formed on both end faces of the p-type thermoelectric conversion layer 110. From the viewpoint of contact resistance, a thermoelectric conversion member having Sb layers 120 on both sides is preferred. Figures 1A to 1C show an example of a member with a long length along the lamination direction, but the p-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 element members can be cut out.

[0034] Thus, the p-type thermoelectric conversion member 100 of the present embodiment is provided with an Sb layer 120 on at least one end surface of a p-type thermoelectric conversion layer 110 made of a p-type thermoelectric material, so that when an electrode is electrically connected to the p-type thermoelectric conversion layer 110 through the Sb layer 120, the electrode contact resistance can be reduced. Further, by using the p-type thermoelectric conversion member 100 of the present embodiment as a thermoelectric conversion element, the electrode contact resistance can be reduced, so that a thermoelectric conversion element with high thermoelectric conversion efficiency can be provided.

[0035] Preferably, the p-type thermoelectric material used for the p-type thermoelectric conversion layer 110 is Mg ｂ Ag ｃ Sb ｄ , Mg ｂ－ｅ B ｅ Ag ｃ Sb ｄ , Mg ｂ Ag ｃ Sb ｄ + fwt% Z, and Mg ｂ－ｅ B ｅ Ag ｃ Sb ｄ + fwt% Z is one or more compounds selected from the group consisting of. B is one or more elements selected from the group consisting of copper (Cu), iron (Fe), zinc (Zn), ytterbium (Yb), and calcium (Ca). Z is stearic acid (C １８ H ３６ O ２ ), palmitic acid (C １６ H ３２ O ２ ), arachidic acid (C ２０ H ４０ O ２ ), zinc stearate (C ３６ H ７０ ZnO ４ ), magnesium stearate (C ３６ H ７０ MgO ４ ), barium stearate (C ３６ H ７０ BaO ４ ), calcium stearate (C ３６ H ７０ CaO ４ ), sodium stearate (C１８ H ３５ NaO ２ ), and N,N'-ethylenedi(stearamide)(C ３８ H ７６ N ２ O ２ It is one or more fatty acids selected from the group consisting of ). Parameters b, c, d, e, and f are preferably 0.95 ≤ b ≤ 1.05, 0.95 ≤ c ≤ 1.05, 0.95 ≤ d ≤ 1.05, 0 < e ≤ 0.1, and 0 < f ≤ 1.0. For example, Mg ｂ Ag ｃ Sb ｄ In a p-type thermoelectric material consisting of the above, 0.95 ≤ b ≤ 1.05, 0.95 ≤ c ≤ 1.05, and 0.95 ≤ d ≤ 1.05 may also be true. Mg ｂ－ｅ B ｅ Ag ｃ Sb ｄ In a p-type thermoelectric material consisting of the above, 0.95 ≤ b ≤ 1.05, 0.95 ≤ c ≤ 1.05, 0.95 ≤ d ≤ 1.05, and 0 < e ≤ 0.1 may also be true. Here, e may be greater than 0 and as small as technically possible. For example, e may be 0.00001 or greater. For example, Mg ｂ Ag ｃ Sb ｄ In a p-type thermoelectric material consisting of +fwt%Z, 0.95 ≤ b ≤ 1.05, 0.95 ≤ c ≤ 1.05, 0.95 ≤ d ≤ 1.05, and 0 < f ≤ 1.0 may also be true. Here, f may be greater than 0 and as small as technically possible. For example, f may be 0.00001 or greater. For example, Mg ｂ－ｅ B ｅ Ag ｃ Sb ｄIn a p-type thermoelectric material consisting of +fwt%Z, the following may be true: 0.95 ≤ b ≤ 1.05, 0.95 ≤ c ≤ 1.05, 0.95 ≤ d ≤ 1.05, 0 < e ≤ 0.1, and 0 < f ≤ 1.0. Here, f may be greater than 0 and technically as small as possible. For example, f may be 0.00001. The same conditions as above apply to e and f. Such a MgAgSb-based thermoelectric material constituting the p-type thermoelectric conversion layer 110 is preferred because it has high electrical conductivity and a high power factor near room temperature (temperature range of 273 K to 320 K).

[0036] More preferably, copper (Cu) and / or zinc (Zn) may be used as element B. This provides a thermoelectric material with improved electrical conductivity at room temperature and an improved power factor.

[0037] More preferably, stearic acid (C) as the fatty acid. １８ H ３６ O ２ It is preferable to use ). Adding fatty acids and / or derivatives of fatty acids to MgAgSb-based thermoelectric materials in this way is preferable because it lowers the thermal conductivity k and improves the dimensionless figure of merit ZT of the thermoelectric material (Reference 1: Energy and Environmental Science, Global Softening to manipulate sound velocity for reliable high-performance MgAgSb thermoelectrics, Airan Li et al., Open Access Article. Published on 18 October 2024).

[0038] The Sb layer 120 may further contain at least one additive element selected from the group consisting of magnesium (Mg), copper (Cu), and bismuth (Bi). This can further reduce the interface resistance (hereinafter referred to as contact resistance) between the MgAgSb-based thermoelectric material and the Sb layer 120. Herein, in the specification of this application, "addition" may mean adding or mixing another type of substance with a substance. The additive element may refer to another type of element (which may mean a different type of substance) that is added to or mixed with the substance. Any method of addition or mixing is acceptable.

[0039] Preferably, Mg is added to the Sb layer 120. As will be described later, elements contained in the MgAgSb thermoelectric material may diffuse from the MgAgSb thermoelectric material to the vicinity of the interface between the Sb layer 120 and the MgAgSb thermoelectric material, and a second phase may precipitate. This can further reduce the contact resistance. Therefore, similar effects can be expected if elements contained in the MgAgSb thermoelectric material are added to the Sb layer 120 as part of the initial composition.

[0040] When elements such as Mg are added in advance as part of the Sb layer's composition, the content of the added elements in the Sb layer 120 may preferably be 0.1 at% or more and 10 at% or less. For example, it may be 0.01 at% or more, 0.02 at% or more, or 0.05 at% or more. It may also be 20 at% or less, 15 at% or less, or 12 at% or less. The content of the added elements is more preferably in the range of 0.3 at% or more and 7 at% or less, and even more preferably in the range of 0.5 at% or more and 5 at% or less. This can further reduce the contact resistance.

[0041] The inventors of this application confirmed by EDX analysis in Examples 13 and 15 of the embodiments described later that Mg diffused from the MgAgSb-based thermoelectric material was added to the Sb layer 120 near the interface at a concentration of approximately 0.1 to 10%, and further confirmed that the contact resistance decreased in this case. Based on this, it can be expected that the contact resistance will be reduced by pre-adding approximately 0.1 to 10% of Mg to the Sb layer 120 and adding Mg to the Sb matrix.

[0042] Preferably, the thickness of the Sb layer 120 may be 50 μm or more and 1000 μm or less. More preferably, the thickness of the Sb layer 120 may be 100 μm or more and 600 μm or less. For example, it may be 10 μm or more, 20 μm or more, 40 μm or more, or 50 μm or more. It may also be 1500 μm or less, 1200 μm or less, or 1100 μm or less. It is possible to maintain stable low contact resistance even under long-term power generation conditions. The thickness of the Sb layer can be determined by observing it at 100x magnification with a scanning electron microscope (SEM) and taking the average value at any three points. For example, by observing at such high magnification, the boundary of the Sb layer is thought to become clear, and if there are fine irregularities, the boundary position can be determined by smoothing it out as is done in normal microscopic observation (for example, linear approximation). Furthermore, the precipitated layer described later here refers to a layer containing a substance produced by the reaction of elements in the thermoelectric conversion layer 110 with Sb, which is the main component of the Sb layer 120. Mainly, elements (e.g., Mg) in the thermoelectric conversion layer 110 may diffuse into the Sb layer, forming an element-rich precipitated phase on the Sb layer side. As shown in Figure 11, the thickness of the precipitated layer can be measured by approximating the boundary between the precipitated layer and the Sb layer or thermoelectric conversion layer with a straight line from a cross-sectional SEM image, and then measuring the thickness from this linearly approximated boundary. The linear approximation can be defined as the point where the median of the concentration difference occurs, by referring to EDX line scans of elements such as Mg, Ag, and Sb near the interface, as shown in Figures 14A and 14B.

[0043] Preferably, the Sb layer 120 has a space group R-3m (the 166th of the International Tables for Crystallography). In this specification, "-3" represents "3 with an overbar". This can further reduce contact resistance.

[0044] Preferably, the p-type thermoelectric conversion layer 110 and the Sb layer 120 are sintered bodies, and the Sb layer 120 is integrally molded with the p-type thermoelectric material by sintering it in contact with the raw material of the p-type thermoelectric material. This can further reduce contact resistance.

[0045] As shown in Figure 1C, the thermoelectric conversion member 100 may further include a precipitate layer 130 between the p-type thermoelectric conversion layer 110 and the Sb layer 120. The precipitate layer 130 contains a substance produced by the reaction of elements in the MgAgSb-based thermoelectric material constituting the p-type thermoelectric conversion layer 110 with Sb, which is the main component of the Sb layer 120. This allows for reduced contact resistance while maintaining thermoelectric conversion efficiency.

[0046] As the precipitate layer 130 may be provided in this manner, in this embodiment, "Sb layer located on at least one end face of the thermoelectric conversion layer" means that the Sb layer 120 may be located directly above the thermoelectric conversion layer 110, or the Sb layer 120 may be located on the thermoelectric conversion layer 110 via the precipitate layer 130.

[0047] The precipitate layer 130 contains at least Mg ３ Sb ２ It contains. Preferably, the precipitate layer 130 is Mg ３ Sb ２ , and / or, Ag ３ May contain Sb. Mg ３ Sb ２ La ２ O ３ It has a structure and belongs to the P-3m1 space group (the 164th in the International Tables for Crystallography). Here again, "-3" represents "3 with an overbar". Ag ３ Sb is Cu ３ It has an Au structure and belongs to the Pmm2 space group (the 25th in the International Tables for Crystallography).

[0048] The precipitate layer 130 is Mg ３ Sb ２ , and / or, Ag ３ It may be composed of Sb, or the Sb layer 120 may be used as the base material and Mg ３ Sb ２ Ag ３ Sb may be distributed in an island-like manner. For example, Sb may migrate from the Sb layer into the p-type thermoelectric conversion layer 110 to form a precipitate layer 130. Mg, Ag, and / or Sb may migrate into the Sb layer 120 to form a precipitate layer 130.

[0049] Furthermore, the precipitated layer 130 may have an Sb metal phase having an R-3m crystalline structure as the matrix phase, to which Mg and / or Ag may be added. Preferably, the concentration of Mg added to the precipitated layer 130 is 1 at% to 10 at%. More preferably, the concentration of Mg added to the precipitated layer 130 is 2 at% to 8 at%. Also, the concentration of Ag added to the precipitated layer 130 is 0.1 at% to 2 at%. More preferably, the concentration of Ag added to the precipitated layer 130 is 0.2 at% to 0.5%. This can further reduce the contact resistance.

[0050] The thickness of the precipitated layer 130 is preferably in the range of 1 μm to 100 μm, and more preferably in the range of 1 μm to 50 μm. This allows for a reduction in contact resistance while maintaining the thermoelectric conversion efficiency of the MgAgSb-based thermoelectric material.

[0051] Between the p-type thermoelectric conversion layer 110 and the Sb layer 120, under the heat treatment or power generation temperature described later, constituent elements within the p-type thermoelectric conversion layer 110 may undergo thermal diffusion. For example, Mg in the p-type thermoelectric conversion layer 110 may diffuse to the Sb layer 120, forming a precipitate layer containing Mg in the Sb matrix. Also, the diffused Mg may react with the Sb in the Sb layer 120, resulting in at least Mg ３ Sb ２ A precipitate layer containing Mg may be formed. The inventors of this application have confirmed that the formation of the precipitate layer does not result in deterioration of thermoelectric properties and that high thermoelectric conversion efficiency can be maintained. They have also confirmed that contact resistance can be further reduced with the formation of the precipitate layer. Therefore, a precipitate layer 130 containing Mg may be formed at the interface by annealing the p-type thermoelectric conversion member 100 of this application, as illustrated in Figures 1A to 1C, for a predetermined period of time or by using it for power generation for a certain period of time.

[0052] Mg diffuses from the MgAgSb-based thermoelectric material constituting the p-type thermoelectric conversion layer 110 to the Sb layer 120. ３ Sb ２While the Ag-rich phase is formed near the interface, the Ag-rich phase and Sb-rich phase may be formed near the interface on the MgAgSb thermoelectric material side. Therefore, the precipitated layer 130 contains the Ag-rich phase and Ag ３ The system may further include at least one phase selected from the group consisting of Sb and the Sb-rich phase.

[0053] Traditionally, Ag ３ Sb is known to adversely affect the performance of MgAgSb-based thermoelectric materials and increase contact resistance, but in experiments conducted by the present inventor, Ag formed near the interface ３ It was confirmed that Sb reduces contact resistance without increasing it. This is because a thin layer of Ag, about a few micrometers thick, is present near the interface. ３ It is believed that the formation of the Sb metallic phase increases the electron density near the interface, lowering the energy barrier between the MgAgSb-based thermoelectric material and leading to a decrease in contact resistance.

[0054] Furthermore, Mg ３ Sb ２ Ag ３ The precipitation of the second phase, such as Sb, occurs within a range of several tens of micrometers from the interface, for example, in a region of 1 μm to 100 μm. Therefore, it does not affect the performance of MgAgSb-based thermoelectric materials far from the interface.

[0055] Therefore, by using the Sb layer 120 of this embodiment, it is possible to provide a thermoelectric conversion element that does not adversely affect the thermoelectric performance of the MgAgSb matrix even under long-term power generation conditions, and improves the electronic structure near the interface, thereby maintaining low contact resistance over a long period of time.

[0056] <Method for Manufacturing Thermoelectric Conversion Members> Figure 2 is a flowchart illustrating an exemplary manufacturing process for a thermoelectric conversion member according to this embodiment.

[0057] The method according to this embodiment includes at least steps S210 and S220.

[0058] In step S210, a laminate is formed of a raw material mixture for a p-type thermoelectric material, which is a mixture of a raw material containing magnesium (Mg), a raw material containing silver (Ag), and a raw material containing antimony (Sb), and a raw material containing Sb as the raw material for the Sb layer 120. Alternatively, a laminate is formed of a p-type thermoelectric material and a raw material containing Sb as the raw material for the Sb layer 120. The p-type thermoelectric material is the same as the MgAgSb-based thermoelectric material described with reference to Figures 1A to 1C, so its description is omitted, but it may be obtained as a commercially available product, or it may be manufactured in advance, for example, by referring to Patent Document 1.

[0059] In step S220, the laminate formed in step S210 is sintered.

[0060] More specifically, in step S210, the raw material containing Mg may be a powder of elemental Mg metal, or it may be elemental Mg metal including at least one of the following forms: sheet, granular, or lump. The raw material containing Ag may be a powder of elemental Ag metal, or it may be elemental Ag metal including at least one of the following forms: sheet, granular, or lump. The raw material containing Sb may be a powder of elemental Sb metal, or it may be elemental Sb metal including at least one of the following forms: sheet, granular, or lump.

[0061] The raw materials containing Mg, Ag, and Sb are mixed so that the Mg, Ag, and Sb satisfy the composition ratio of the MgAgSb-based thermoelectric material described above, and then pulverized by ball milling.

[0062] The raw material mixture for the p-type thermoelectric material may further contain at least one raw material selected from the group consisting of raw materials containing Cu, raw materials containing Fe, raw materials containing Zn, raw materials containing Yb, and raw materials containing Ca. These raw materials may also be powders of the respective metals, or they may be metals in the form of at least one of the following: sheets, granules, or lumps.

[0063] The raw material mixture for p-type thermoelectric materials is stearic acid (C １８ H ３６ O ２), palmitic acid (C １６ H ３２ O ２ ), aicosanoic acid (C ２０ H ４０ O ２ ), zinc stearate (C ３６ H ７０ ZnO ４ ), magnesium stearate (C ３６ H ７０ MgO ４ ), barium stearate (C ３６ H ７０ BaO ４ ), calcium stearate (C ３６ H ７０ CaO ４ ), sodium stearate (C １８ H ３５ NaO ２ ), and N,N'-ethylenedi(stearamide)(C ３８ H ７６ N ２ O ２ It may contain one or more fatty acids selected from the group consisting of ).

[0064] In step S210, the raw material for the Sb layer may be powder of elemental Sb metal, or it may be elemental Sb metal containing one or more forms from sheet, granule, or lump. The raw material for the Sb layer may further contain raw materials selected from the group consisting of raw materials containing Mg, raw materials containing Cu, and raw materials containing Bi. These raw materials may also be powder of elemental metal, or they may be elemental metals containing at least one of the forms from sheet, granule, or lump. The amount of added metal elements may be 0.01 at% or more, 0.02 at% or more, or 0.05 at% or more, or 20 at% or less, 15 at% or less, or 12 at% or less, or it may be prepared to be in the range of 0.1 at% to 10 at%.

[0065] Figure 3 shows a sintering method for a laminate.

[0066] Step S210 will be explained in more detail using Figure 3. The raw material 510 for the Sb layer is placed on the upper surface of the punch 540 fitted into the die 530 for pressure molding, so that the surface is flat. On top of that, the raw material mixture 520 for the p-type thermoelectric material is placed on top, so that the surface is flat. Then, the raw material 510 for the Sb layer is placed on top again, and the powder of the raw materials is leveled so that the surface is flat. In this way, the raw material 510 for the Sb layer, the raw material mixture 520 for the p-type thermoelectric material, and the raw material 510 for the Sb layer are stacked in a sandwich structure. If the Sb layer is to be formed only on one end face of the p-type thermoelectric material, the raw material 510 for the Sb layer and the raw material mixture 520 for the p-type thermoelectric material can be stacked one layer at a time. After stacking, the punch 550 is fitted into the die 530 and placed in the press machine, and pressure molding is started.

[0067] In step S210, instead of the raw material mixture 520 of the p-type thermoelectric material, a commercially available p-type thermoelectric material that has been pre-mixed in a predetermined composition ratio may be used.

[0068] The sintering in step S220 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 (for example, the interface between the Sb layer and the p-type thermoelectric conversion layer).

[0069] Preferably, the sintering temperature in step S220 may be 450K or higher, 470K or higher, or 480K or higher, or 630K or lower, 620K or lower, or 610K or lower, or within a temperature range of 500K to 600K. SPS may be performed at any of the above temperature ranges at a pressure of 42MPa or higher, 45MPa or higher, or 48MPa or higher, or 78MPa or lower, 75MPa or lower, or 72MPa or lower, or within a pressure range of 50MPa to 70MPa. This makes it possible to promote sintering while suppressing the phase transition of the MgAgSb-based thermoelectric material that may occur at temperatures higher than 600K. More preferably, SPS may be performed at 573K at 60MPa for 5 minutes. This makes it possible to manufacture with a good yield in a short time.

[0070] In this embodiment, a mixture of p-type thermoelectric materials and the raw materials for the Sb layer 120 are sequentially added to a pressurized container and stacked, and then heat-pressure molding is performed. In this way, the sintering process of the p-type thermoelectric conversion layer 110 and the bonding of the p-type thermoelectric conversion layer 110 and the Sb layer 120 are performed in the same process at once, which simplifies the manufacturing process, reduces manufacturing costs, and provides an integrally molded thermoelectric conversion member 100.

[0071] Following step S220, preferably, the sintered body obtained by sintering a laminate of the p-type thermoelectric material and the Sb layer is annealed in air. The annealing is preferably carried out at a temperature range of 500K to 650K for a period of 30 minutes to 50 days. Preferably, the annealing is carried out at a temperature range of 500K to 600K for about 7 to 30 days. This suppresses the phase transition of the MgAgSb-based thermoelectric material that may occur at temperatures higher than 600K, while also obtaining the effects of annealing described later.

[0072] In this embodiment, by performing annealing (aging) at a temperature equivalent to the power generation temperature, Mg in the MgAgSb thermoelectric material diffuses to the Sb layer, forming the aforementioned precipitate layer. This further reduces contact resistance and improves thermoelectric conversion efficiency. However, the manufacturing method of this embodiment does not require annealing, and the thermoelectric conversion member of this embodiment is not limited to one that has undergone annealing. This is because an effect equivalent to annealing is expected at the power generation temperature.

[0073] The method for manufacturing the p-type thermoelectric conversion member 100 is not limited to the method described above. As another example, the p-type thermoelectric conversion member 100 may be manufactured by placing the raw material for the Sb layer described above on at least one end face of a sintered body made of MgAgSb thermoelectric material and sintering it. The sintering can be carried out using step S220 in Figure 2. Here as well, the raw material for the Sb layer may be placed on both sides of the sintered body.

[0074] As another example, the above-mentioned Sb layer may be formed on at least one end face of a sintered body made of MgAgSb thermoelectric material by one or more methods 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. Here too, the Sb layer may be formed on both sides of the sintered body.

[0075] In the above description, we explained a configuration in which the p-type thermoelectric conversion layer 110 is made of a sintered body and a metal layer of the Sb layer 120 is formed on the sintered body. However, as another configuration, the p-type thermoelectric conversion layer 110 and the Sb layer 120 may each be made of a flexible shape.

[0076] That is, the p-type thermoelectric conversion layer 110 is made of a mixture of MgAgSb-based thermoelectric material and an organic material, and may be a flexible layer. Similarly, the Sb layer 120 is made of a mixture of a material mainly composed of Sb and an organic material, and may be a flexible layer.

[0077] Here, the organic material may be at least one organic material selected from the group consisting of poly(3,4-ethylenedioxythiophene)polystyrene sulfonic acid (PEDOT:PSS), poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT), polyaniline (PANI), tetrathiafulvalene (TTF), and benzodifrafranone-paraphenylenevinylidene (BDPPV). Any of these can provide a flexible layer.

[0078] Furthermore, the MgAgSb-based thermoelectric material and the material mainly composed of Sb 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%, more preferably 4 wt% to 10 wt%, and even more preferably 4 wt% to 7 wt%. This allows for the provision of a film-type thermoelectric conversion member with more desirable flexibility.

[0079] Flexible thermoelectric conversion components are manufactured by simply laminating a flexible p-type thermoelectric conversion layer with a flexible Sb layer.

[0080] (Second Embodiment) The second embodiment describes a thermoelectric conversion element using the p-type thermoelectric conversion member 100 of the first embodiment. In the following, examples are shown in which the p-type thermoelectric conversion member 100 is applied to a single element or a π-type thermoelectric conversion element, but the embodiments are not limited to these examples, and the p-type thermoelectric conversion member 100 may be incorporated into other types of thermoelectric conversion elements.

[0081] Figure 4 is a schematic diagram showing a single-element thermoelectric conversion element 200.

[0082] As shown in Figure 4, the thermoelectric conversion element 200 of this embodiment comprises at least a p-type thermoelectric conversion member 100. The thermoelectric conversion element 200 also comprises electrodes 150 and 160 at each end of the p-type thermoelectric conversion member 100. The electrodes 150 and 160 may be made of commonly used electrode materials, and may include at least one of the following: Fe, Ag, Al, Ni, Cu, etc. In the example in Figure 4, the thermoelectric conversion member 100 is connected to the electrode 160 on the low-temperature side by solder or the like. The end of the p-type thermoelectric conversion member 100 opposite to the electrode 160 is connected to the electrode 150 on the high-temperature side.

[0083] When the thermoelectric conversion element 200 is installed in an environment where electrode 150 is at a high temperature and electrode 160 is at a lower temperature than electrode 150, and electrodes 150 and 160 are connected to an external electrical circuit, a voltage is generated due to the Seebeck effect, and current flows in the direction of electrode 150, p-type thermoelectric conversion member 100, and electrode 160, as shown by the arrows in Figure 4.

[0084] In Figure 4, by using the p-type thermoelectric conversion member 100 of this embodiment, low contact resistance can be achieved between the electrodes 150 and 160, and the increase in contact resistance is suppressed even at operating temperatures, thereby achieving high thermoelectric conversion efficiency.

[0085] Figure 5 is a schematic diagram showing a π-type thermoelectric conversion element 300.

[0086] As shown in Figure 5, the thermoelectric conversion element 300 includes n-type thermoelectric conversion members 400 that are alternately connected in series with p-type thermoelectric conversion members 100. The n-type thermoelectric conversion members 400 and the p-type thermoelectric conversion members 100 are electrically connected in series with a low-temperature electrode 320 and a high-temperature electrode 310 in between. The n-type thermoelectric conversion member 400 includes an n-type thermoelectric conversion layer 410 made of an n-type thermoelectric material, and metallization layers 420 are formed at both ends of the n-type thermoelectric conversion layer 410.

[0087] The n-type thermoelectric material constituting the n-type thermoelectric conversion layer 410 is not particularly limited, but it is preferable to use one with high thermoelectric performance at 500K or below, especially at room temperature (for example, ZT of 0.4 to 1.6). For example, the n-type thermoelectric material is Mg ２ Sb ３ system, BiTeSe system, CoSb３ system, Mg ２ Examples include (Si, Sn) systems. Mg ２ Sb ３ An example composition of the system is, for example, Mg ３．２ Sb １．５ Bi ０．５ Te ０．０１ An example composition of the BiTeSe system is, for example, Bi ２ Te ２．７ See ０．３ CoSb ３ An example of the system's composition is, for example, CoSb ３ Si ０．０７５ Te ０．１７５ Mg ２ An example composition of the (Si,Sn) system is, for example, Mg ２ Si ０．３ Sn ０．７ These are just examples and not limiting.

[0088] The metallization layer 420 is a layer that reduces the contact resistance between the n-type thermoelectric conversion layer 410 and the electrodes 310 and 320. For the material of the metallization layer 420, for example, stainless steel (SUS) may be used, but other materials may also be used.

[0089] Electrodes 310 and 320 can be made of commonly used electrode materials, for example, materials containing at least one of the following: Fe, Ag, Al, Ni, Cu, etc.

[0090] As shown in Figure 5, when the thermoelectric conversion element 300 is installed in an environment where electrode 310 is at a high temperature and electrode 320 is at a lower temperature than electrode 310, and electrodes 310 and 320 are connected to an external electrical circuit, a voltage is generated due to the Seebeck effect, and current flows in the direction of electrode 320, n-type thermoelectric conversion member 400, electrode 310, and p-type thermoelectric conversion member 100, as indicated by the arrows in Figure 5. In detail, electrons in the n-type thermoelectric conversion layer 410 gain thermal energy from the high-temperature electrode 310 and move to the low-temperature electrode 320, releasing thermal energy, while holes in the p-type thermoelectric conversion layer 110 gain thermal energy from the high-temperature electrode 310 and move to the low-temperature electrode 320, releasing thermal energy, thereby generating a current in the thermoelectric conversion element 300.

[0091] Although Figure 5 shows an example of a π-type thermoelectric power generation 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 p-type thermoelectric conversion member 100 and the n-type thermoelectric conversion member 400 are connected alternately in series.

[0092] In Figure 5, by using the p-type thermoelectric conversion member 100 of this embodiment, low contact resistance can be achieved between the electrodes 310 and 320, and the increase in contact resistance is suppressed even at operating temperatures, thereby achieving high thermoelectric conversion efficiency.

[0093] Next, specific examples will be shown, but the present invention is not limited to these examples.

[0094] [Raw materials] As a p-type thermoelectric material, MgAg ０．９７ Sb ０．９９ MgAgSb １．０２ MgAg １．０１ Sb １．０４ , and Mg ０．９８ Zn ０．０２ Ag ０．９７ Sb ０．９９ A mixture of each of these was prepared with stearic acid as the fatty acid.

[0095] As raw materials for the p-type thermoelectric material, we used Mg (powder, model number 13112, purity 99%, manufactured by Sigma-Aldrich Japan LLC), Ag (granules, model number 327050, purity 99.99%, manufactured by Sigma-Aldrich Japan LLC), Sb (lump, model number 452343, purity 99.999%, manufactured by Sigma-Aldrich Japan LLC), and Zn (granules, model number 402583, purity 99.99%, manufactured by Sigma-Aldrich Japan LLC). Each raw material was weighed to satisfy the respective composition ratios of the p-type thermoelectric material shown in Table 1, and stearic acid (model number 85679, manufactured by Sigma-Aldrich Japan LLC) was added in the weight percentage shown in Table 1 and mixed to obtain the raw material mixture for the p-type thermoelectric material. Specifically, each raw material was mixed with stearic acid and mixed in a ball mill for 5 hours. As raw materials for the Sb layer, Sb (lump, model number 452343, purity 99.999%, manufactured by Sigma-Aldrich Japan LLC), Cu (powder, model number 203122, purity 99.99%, manufactured by Sigma-Aldrich Japan LLC), and Bi (granules, model number 95372, purity 99.99%, manufactured by Sigma-Aldrich Japan LLC) were used. The amounts of each metal listed in Table 1 were mixed and mixed in a ball mill for 2 hours.

[0096] [Examples 1 to 15: Thermoelectric Conversion Members] In Examples 1 to 15, a one-step SPS sintering process, as shown in Figure 2, was performed using the p-type thermoelectric material (MgAgSb-based thermoelectric material) and a material mainly composed of Sb shown in Table 1 to produce thermoelectric conversion members with an Sb layer / MgAgSb-based thermoelectric material / Sb layer. The obtained samples are referred to as the thermoelectric conversion members of Examples 1 to 15, respectively.

[0097] In detail, the raw material for the Sb layer 510 (Figure 3), the raw material mixture for the p-type thermoelectric material 520 (Figure 3), and the raw material for the Sb layer 510 (Figure 3) were sequentially layered and placed into the punch 540 (Figure 3) of the carbon die 530 (Figure 3), and the punch 550 (Figure 3) was inserted, and a single-stage pressure molding was performed by discharge plasma sintering (SPS, manufactured by Fuji Denpa Koki Co., Ltd., Doctor Lab Series 322La). The heating rate of the SPS was 1 K / second in all examples. The pressurizing conditions for the SPS were a holding temperature of 573 K, a holding pressure of 60 MPa, and a sintering time (holding time) of 5 minutes in all examples.

[0098] Next, the thermoelectric conversion members of Examples 13 to 15 were annealed under the conditions shown in Table 1. Note that for the thermoelectric conversion members of Examples 1 to 12, even if the cooling time after SPS is considered as annealing, it is less than 30 minutes, so they can be considered as being annealed (i.e., approximately as-annealed).

[0099] The interface of the thermoelectric conversion members in Examples 1 to 15 was observed using a scanning electron microscope (SEM, Hitachi, Ltd., model SU8000). Furthermore, compositional analysis was performed on the precipitated layer formed near the interface between the p-type thermoelectric conversion layer and the Sb layer using energy-dispersive X-ray spectroscopy (EDX) attached to the SEM. The contact resistivity of the thermoelectric conversion materials in Examples 1 to 15 was also measured using a biaxial resistance distribution analyzer (Mottainai Energy Co., Ltd., S1331). These results are shown in Figures 6 to 14B and Table 2.

[0100]

[0101]

[0102] Figure 6 is an SEM image showing the interface of the thermoelectric conversion member in Example 1. Figure 7 is a diagram showing the EDX mapping of Mg in Figure 6. Figure 8 is a diagram showing the EDX mapping of Ag in Figure 6. Figure 9 is a diagram showing the EDX mapping of Sb in Figure 6. Figure 10 is an SEM image showing the interface of the thermoelectric conversion member in Example 15. Figure 11 is a diagram showing the EDX mapping of Mg in Figure 10. Figure 12 is a diagram showing the EDX mapping of Ag in Figure 10. Figure 13 is a diagram showing the EDX mapping of Sb in Figure 10.

[0103] Figures 7-9 and 11-13 are shown in grayscale, with brightly lit areas indicating the presence of each element. As shown in Figures 6-9, the interface between the Sb layer and the MgAgSb-based thermoelectric material in Example 1 formed a good and clear bonding interface, and it was confirmed that no cracks or delamination occurred. It was confirmed that Mg and Ag were uniformly distributed only in the region of the thermoelectric conversion layer made of the MgAgSb-based thermoelectric material. The thickness of the Sb layer was 500 μm, and its crystal structure was R-3m. Although not shown, in the thermoelectric conversion members of Examples 2-12, similarly, the interface between the Sb layer and the MgAgSb-based thermoelectric material formed a good and clear bonding interface, and it was confirmed that no cracks or delamination occurred. Furthermore, in the thermoelectric conversion members of Examples 1-12, the formation of a precipitate layer at the interface between the Sb layer and the MgAgSb-based thermoelectric material was not observed (see Table 2).

[0104] This demonstrates that the manufacturing method shown in Figure 2 provides an integrally molded thermoelectric conversion member comprising a thermoelectric conversion layer made of a p-type thermoelectric material containing magnesium (Mg), silver (Ag), and antimony (Sb), and Sb layers located on both ends of the thermoelectric conversion layer.

[0105] As shown in Figures 10 to 13, in the thermoelectric conversion member of Example 15 after long-term annealing, the formation of a precipitate layer was confirmed between the Sb layer and the MgAgSb-based thermoelectric material, but no cracks or delamination occurred, indicating a good bonding interface. Furthermore, as shown in Figures 11 to 13, even after long-term annealing, no diffusion of Sb from the MgAgSb-based thermoelectric material to the Sb layer was observed, which can be a factor in performance degradation. In other words, it is suggested that by using an Sb metallization layer, the diffusion and departure of Sb from the MgAgSb-based thermoelectric material, which has been a problem in the past, can be suppressed, and the resulting deterioration of the properties of the p-type thermoelectric material can be suppressed.

[0106] On the other hand, as shown in Figure 11, it was confirmed that Mg diffused from the MgAgSb-based thermoelectric material to the Sb layer, forming an Mg-rich precipitate layer on the Sb layer side.

[0107] Figures 14A and 14B show the EDX line scans of Mg, Ag, and Sb near the interface between the Sb layer of the thermoelectric conversion member in Example 1 and Example 15 and the MgAgSb-based thermoelectric material.

[0108] Figure 14A shows the EDX line scan of the thermoelectric conversion member of Example 1, and Figure 14B shows the EDX line scan of the thermoelectric conversion member of Example 15. As shown in Figure 14B, even after 30 days of annealing, no diffusion of Sb from the thermoelectric conversion layer (right side) made of MgAgSb-based thermoelectric conversion material to the Sb layer (left side) was observed. In other words, it was confirmed that Sb does not diffuse from the p-type thermoelectric conversion layer to the Sb layer even after undergoing heat treatment equivalent to that performed during long-term power generation.

[0109] On the other hand, EDX line scanning revealed the diffusion of Mg and Ag from the thermoelectric conversion layer, which is made of MgAgSb-based thermoelectric material, to the Sb layer. Thus, precipitate layers containing Mg-rich and Ag-rich phases can be formed at the interface between the Sb layer and the MgAgSb-based thermoelectric material. According to compositional analysis, the Mg-rich phase is mainly composed of Mg ３ Sb ２ Therefore, the Ag-rich phase is mainly Ag ３ It was Sb.

[0110] As a result, as shown in Examples 13 and 15 of Table 2, the thickness of the Sb layer was partially reduced, and a precipitated layer with a thickness of approximately 5 μm to 30 μm was formed. Although not shown in the figures, it was also confirmed that a precipitated layer was formed at the interface between the Sb layer and the thermoelectric conversion layer in the thermoelectric conversion member of Example 14. In particular, as shown in Figure 11, the precipitated layer had the Sb layer as the base material, with Mg mainly formed in island-like formations within it. ３ Sb ２ Phase and small amounts of Ag ３ The presence of an Sb phase was confirmed. Furthermore, EDX analysis confirmed that the precipitated layer contains a phase doped with Mg and Ag in the matrix phase of the Sb layer.

[0111] As described above in the embodiment, the formation of the precipitated layer is considered to contribute to reducing the interfacial contact resistance between the Sb layer and the thermoelectric conversion layer.

[0112] Figure 15 shows the annealing time dependence of the contact resistivity of the thermoelectric conversion elements of Example 1 and Examples 13 to 15.

[0113] As shown in Table 2, the thermoelectric conversion members in Examples 1 to 15 all have a contact resistivity of 30 μΩcm. ２ It fell below that level. As explained with reference to Figures 6 to 13, this indicates that the Sb layer is a good metallization layer that reduces contact resistivity.

[0114] Furthermore, in the thermoelectric conversion members of Examples 5 to 7 and Example 11, 0.5 to 5 at% of Cu was added to the Sb layer, but the contact resistivity was lower, all of which was 10 μΩcm. ２ It fell below [value]. This indicates that the Sb layer preferably contains Sb as the main component, with Cu further added.

[0115] According to Figure 15, the contact resistivity ρ increases with increasing annealing time. ｃ It gradually decreased, reaching 7.9 μΩcm after 30 days. ２ It decreased to this extent. Thus, the contact resistivity ρ at the interface between the Sb layer and the MgAgSb-based thermoelectric material ｃ The contact resistance decreased without increasing as the annealing time at 573K increased. This confirmed that the interface between the Sb layer and the MgAgSb-based thermoelectric material can maintain stable and low contact resistance over the long term. The Sb layer was found to be advantageous compared to the Ag metallization layer described in Non-Patent Document 1 in that it maintains a low contact resistivity over the long term.

[0116] [Examples 16-17: Thermoelectric Conversion Elements] In Examples 16-17, thermoelectric conversion elements shown in Figure 16 were manufactured using the thermoelectric conversion members from Examples 1-15.

[0117] Figure 16 is a schematic diagram showing the thermoelectric conversion element 600.

[0118] A thermoelectric conversion element 600 was fabricated, containing two pairs of n-type thermoelectric conversion members 400 and p-type thermoelectric conversion members 100, and its thermoelectric conversion efficiency was evaluated. Note that in Figure 16, the electrodes 310 and 320 shown in Figure 5 are omitted from the illustration.

[0119] First, as preparation for the element, take a p-type thermoelectric conversion component from Example 1 or Example 15, approximately 3.8 × 3.8 × 6 mm ３Two p-type thermoelectric conversion members 100 were fabricated by cutting out two rectangular parallelepiped shapes from each. On the other hand, for the n-type thermoelectric conversion member 400, Mg was used as the n-type thermoelectric conversion layer 410. ３ Sb ０．６ Bi １．４ For the metallization layer 420, stainless steel SUS304 was used. SUS304 / Mg ３ Sb ０．６ Bi １．４ A sandwich structure of SUS304 was formed, and an n-type thermoelectric conversion member 400 of approximately the same size as the p-type thermoelectric conversion member 100 was fabricated. Then, as illustrated in Figure 5, the p-type thermoelectric conversion member 100 and the n-type thermoelectric conversion member 400 were electrically connected in series at the high-temperature side electrode and the low-temperature side electrode to fabricate a π-type two-pair thermoelectric conversion element 600.

[0120] The thermoelectric conversion efficiency of the thermoelectric conversion element 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 80 K to 300 K, and measurements were taken under vacuum conditions. The results are shown in Figures 17 and 18.

[0121] Figure 17 is a graph showing the thermoelectric conversion efficiency η of a π-type two-pair thermoelectric conversion element using the thermoelectric conversion member of Example 1. Figure 18 is a graph showing the thermoelectric conversion efficiency η of a π-type two-pair thermoelectric conversion element using the thermoelectric conversion member of Example 15.

[0122] As shown in Figure 17, a maximum conversion efficiency of 7.6% was obtained at a temperature difference of 276 K, demonstrating that the thermoelectric conversion element using the thermoelectric conversion member of Example 1 exhibited a sufficiently high thermoelectric conversion efficiency.

[0123] Although not shown in the diagram, an attempt was made to fabricate a π-type single-pair thermoelectric conversion element without an Sb layer, but it was unsuccessful. Specifically, from the p-type thermoelectric conversion member of Example 1, approximately 3.8 × 3.8 × 6 mm ３ We cut out a rectangular parallelepiped and attempted to solder metal electrodes (electrodes 150 and 160 shown in Figure 4) made of Fe, Ag, Al, Ni, Cu, etc., but the wettability was poor and we were unable to join the two.

[0124] This indicates that the Sb layer exhibits good bonding properties with MgAgSb-based thermoelectric materials, enabling a good soldering state and functioning as a suitable metallization layer. Furthermore, it was shown that using the Sb layer as a metallization layer can reduce contact resistivity, thereby improving thermoelectric conversion efficiency.

[0125] As shown in Figure 18, the thermoelectric conversion efficiency η of the thermoelectric conversion element using the thermoelectric conversion member of Example 15 after 30 days of annealing reached a maximum conversion efficiency of approximately 8.2% at a temperature difference of 294 K, which was an improvement over the maximum conversion efficiency of 7.6% for Example 2 shown in Figure 7. This indicates that the contact resistivity is further reduced by the formation of a precipitated layer through annealing, and the thermoelectric conversion efficiency is further improved.

[0126] Conventionally, as shown in Non-Patent Document 1, thermoelectric elements using Ag as the metallization layer have had the problem of the conversion efficiency decreasing with the heat treatment time. However, by using the Sb layer of this embodiment, a unique result was obtained in which the conversion efficiency did not decrease, but rather improved, under the same thermal environment as long-term power generation.

[0127] Thus, the Sb layer functions as a good metallization layer for the MgAgSb-based thermoelectric material, and the low contact resistance and high thermoelectric conversion efficiency shown in the initial stage can be maintained even after a long-term annealing environment of 30 days. Furthermore, this embodiment overcomes the problem of performance degradation caused by the diffusion migration of Sb from the MgAgSb-based thermoelectric material to the metallization layer, as described in Non-Patent Document 1, for example.

[0128] 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.

[0129] 100 p-type thermoelectric conversion member 110 p-type thermoelectric conversion layer 120 Sb layer 200, 300, 600 thermoelectric conversion element 400 n-type thermoelectric conversion member 410 n-type thermoelectric conversion layer 420 metallization layer 150, 160, 310, 320 electrode 510 raw material for Sb layer 520 mixture of p-type thermoelectric material

Claims

1. A thermoelectric conversion member comprising: a thermoelectric conversion layer made of a p-type thermoelectric material containing at least magnesium (Mg), silver (Ag), and antimony (Sb); and an Sb layer located on at least one end face of the thermoelectric conversion layer.

2. The thermoelectric conversion member according to claim 1, wherein the Sb layer further comprises at least one additive element selected from the group consisting of magnesium (Mg), copper (Cu), and bismuth (Bi).

3. The thermoelectric conversion member according to claim 2, wherein the content of the additive element added to the Sb layer is 0.1 at% or more and 10 at% or less.

4. The thermoelectric conversion member according to any one of claims 1 to 3, wherein the thickness of the Sb layer is 50 μm or more and 1000 μm or less.

5. The p-type thermoelectric material is Mg ２ , １８ , ７０ , ２ , ７６ , ３８ , ３５ , ４ , ３６ , ２ Ag ｃ Sb ｄ 、Mg ｂ－ｅ B ｅ Ag ｃ Sb ｄ 、Mg ｂ Ag ｃ Sb ｄ + fwt% Z, and Mg ｂ－ｅ B ｅ Ag ｃ Sb ｄ + fwt% Z, and is one or more compounds selected from the group consisting of: B is one or more elements selected from the group consisting of copper (Cu), iron (Fe), zinc (Zn), ytterbium (Yb), and calcium (Ca); Z is stearic acid (C １８ H ３６ O ２ ), palmitic acid (C １６ H ３２ O ２ ), arachidic acid (C ２０ H ４０ O ２ ), zinc stearate (C ３６ H ７０ ZnO ４ ), magnesium stearate (C ３６ H ７０ MgO ４ ), barium stearate (C ３６ H ７０ BaO ４ ), calcium stearate (C ３６ H ７０ CaO ４ ), sodium stearate (C １８ H ３５ NaO ２ ), and N,N'-ethylenebis(stearamide) (C ３８ H ７６ N ２ O ２ A thermoelectric conversion member according to any one of claims 1 to 4, wherein one or more fatty acids are selected from the group consisting of ), and the parameters b, c, d, e, and f satisfy 0.95 ≤ b ≤ 1.05, 0.95 ≤ c ≤ 1.05, 0.95 ≤ d ≤ 1.05, 0 < e ≤ 0.1, and 0 < f ≤ 1.

0.

6. The thermoelectric conversion member according to any one of claims 1 to 5, wherein the thermoelectric conversion layer and the Sb layer are sintered bodies.

7. Between the thermoelectric conversion layer and the Sb layer, at least Mg ３ Sb ２ A thermoelectric conversion member according to any one of claims 1 to 6, further comprising a precipitate layer containing the above.

8. The thermoelectric conversion member according to claim 7, wherein the thickness of the precipitated layer is in the range of 1 μm or more and 50 μm or less.

9. The thermoelectric conversion member according to any one of claims 1 to 8, wherein the Sb layer belongs to the space group R-3m.

10. The thermoelectric conversion member according to any one of claims 1 to 9, wherein the Sb layer is located on both ends of the thermoelectric conversion layer.

11. A method for manufacturing a thermoelectric conversion member according to any one of claims 1 to 10, comprising: mixing a raw material mixture for the p-type thermoelectric material, which is a mixture of a raw material containing magnesium (Mg), a raw material containing silver (Ag), and a raw material containing antimony (Sb); or forming a laminate of the p-type thermoelectric material and a raw material containing Sb as a raw material for the Sb layer; and sintering the laminate.

12. The method according to claim 11, wherein the sintering is performed by discharge plasma sintering.

13. The method according to claim 12, wherein the sintering is performed by sintering the laminate at a temperature range of 500 K to 600 K and a pressure range of 50 MPa to 70 MPa.

14. The method according to any one of claims 11 to 13, further comprising annealing the sintered body obtained by the sintering in air.

15. The method according to claim 14, wherein the annealing is performed on the sintered body at a temperature range of 500 K to 600 K for a period of 30 minutes to 50 days.

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

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

18. The thermoelectric element according to claim 17, comprising n-type thermoelectric elements connected alternately in series with the p-type thermoelectric elements.

19. The n-type thermoelectric conversion member is Mg ２ Sb ３ system, BiTeSe system, CoSb ３ System, and Mg ２ The thermoelectric conversion element according to claim 18, comprising an n-type thermoelectric material selected from the group consisting of (Si, Sn) systems.

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