Thermoelectric conversion element, thermoelectric conversion module, thermoelectric conversion system, power generation method, and method for manufacturing thermoelectric conversion element

Abstract

Provided is a thermoelectric conversion element which is advantageous from the perspective of reducing the resistance of the thermoelectric conversion element. This thermoelectric conversion element (10a) is provided with a first metal layer (12a), a second metal layer (12b), and a thermoelectric conversion layer (11) disposed between the first metal layer (12a) and the second metal layer (12b) in the thickness direction of the first metal layer (12a). The thermoelectric conversion layer (11) contains a thermoelectric conversion material, and the thermoelectric conversion material contains Mg. The first metal layer 12a contains ceramic particles 12p. The ceramic particles (12p) are arranged inside the first metal layer (12a).

Description

Technical Field

[0001] The present disclosure relates to a thermoelectric conversion element, a thermoelectric conversion module, a thermoelectric conversion system, a power generation method, and a method for manufacturing a thermoelectric conversion element. Background Art

[0002] Conventionally known thermoelectric conversion elements are known. For example, a thermoelectric conversion module can be provided by electrically connecting an N-type thermoelectric conversion element containing an N-type thermoelectric conversion material and a P-type thermoelectric conversion element containing a P-type thermoelectric conversion material. In order to facilitate the electrical bonding of the thermoelectric conversion element, it is known to form a layer of a metal material on the end face portion of the thermoelectric conversion material. A thermoelectric conversion element including a thermoelectric conversion material having such an end face portion is easy to handle and assemble.

[0003] For example, Patent Document 1 describes a magnesium-antimony-based thermoelectric element. The thermoelectric element includes: a magnesium-antimony-based thermoelectric material matrix layer located at the center of the thermoelectric element; a transition layer attached to both surfaces of the matrix layer; and an electrode layer attached to the surfaces of the two transition layers. The material of the transition layer is a magnesium-copper alloy and / or a magnesium-aluminum alloy. The material of the electrode layer is copper.

[0004] Patent Document 2 describes a magnesium-antimony-based thermoelectric element. The thermoelectric element includes: a magnesium-antimony-based thermoelectric material matrix layer located at the center of the thermoelectric element; a transition layer attached to both surfaces of the matrix layer; and an electrode layer attached to the surfaces of the two transition layers. The material of the transition layer is a titanium-copper alloy or a magnesium-copper alloy. The electrode layer is copper and / or nickel.

[0005] Patent Document 3 describes a thermoelectric conversion element including an electrode, an intermediate layer, and a thermoelectric conversion layer. The intermediate layer is provided between the thermoelectric conversion layer and the electrode. The intermediate layer is in contact with the thermoelectric conversion layer. The thermoelectric conversion layer contains at least one element selected from Mg, Sb, and Bi and at least one element selected from Se and Te. The electrode is made of a CuZn alloy. The composition of the intermediate layer is different from the composition of the electrode and the composition of the thermoelectric conversion layer. The intermediate layer contains Cu, Zn, and Mg.

[0006] Patent Document 4 describes a polycrystalline magnesium silicide-based thermoelectric conversion material in which silicon carbide is present in the crystal grains.

[0007] Patent Document 5 describes a thermoelectric conversion material composed of a sintered body of an alloy containing at least two or more elements selected from the elements Bi, Te, Se, and Sb. Regarding this thermoelectric conversion material, a predetermined non-oxide ceramic particle is contained in the sintered body, and a part or all of the non-oxide ceramic particles are present in the crystal grains of the alloy phase.

[0008] Prior Art Documents

[0009] Patent Documents

[0010] Patent Document 1: Specification of Chinese Patent No. 111613715

[0011] Patent Document 2: Specification of Chinese Patent No. 110635020

[0012] Patent Document 3: International Publication No. 2020 / 003554

[0013] Patent Document 4: Japanese Unexamined Patent Application Publication No. 2020-167317

[0014] Patent Document 5: Japanese Unexamined Patent Application Publication No. 9-74229 Summary of the Invention

[0015] The present disclosure provides a thermoelectric conversion element that is advantageous from the viewpoint of reducing the resistance of a thermoelectric conversion element including a Mg-containing thermoelectric conversion material.

[0016] The thermoelectric conversion element of the present disclosure

[0017] includes a first metal layer, a second metal layer, and a thermoelectric conversion layer. The thermoelectric conversion layer is disposed between the first metal layer and the second metal layer in the thickness direction of the first metal layer and includes a thermoelectric conversion material containing Mg.

[0018] The first metal layer includes ceramic particles.

[0019] The ceramic particles are disposed inside the first metal layer.

[0020] According to the present disclosure, it is possible to provide a thermoelectric conversion element including a Mg-containing thermoelectric conversion material that is advantageous from the viewpoint of reducing the resistance of the thermoelectric conversion element. Brief Description of the Drawings

[0021] Figure 1A is a cross-sectional view schematically showing an example of the thermoelectric conversion element of Embodiment 1.

[0022] Figure 1B is a cross-sectional view schematically showing another example of the thermoelectric conversion element.

[0023] Figure 1C is a cross-sectional view schematically showing still another example of the thermoelectric conversion element.

[0024] Figure 1D is a cross-sectional view schematically showing still another example of the thermoelectric conversion element.

[0025] Figure 1E is a cross-sectional view schematically showing still another example of the thermoelectric conversion element.

[0026] Figure 1FIt is a cross-sectional view schematically showing another example of a thermoelectric conversion element.

[0027] Figure 2 It is a view schematically showing a La2O3 type crystal structure.

[0028] Figure 3 It is a flowchart showing a method for manufacturing a thermoelectric conversion element according to Embodiment 1.

[0029] Figure 4 It is a cross-sectional view showing an example of a thermoelectric conversion module according to Embodiment 2.

[0030] Figure 5 It is a cross-sectional view showing another example of a thermoelectric conversion module according to Embodiment 2.

[0031] Figure 6 It is a cross-sectional view showing yet another example of a thermoelectric conversion module according to Embodiment 2.

[0032] Figure 7 It is a side view showing a thermoelectric conversion system according to Embodiment 3.

[0033] Figure 8 It is a photograph of a thermoelectric conversion element according to Example 1.

[0034] Figure 9 It is a view schematically showing a method for measuring the resistance of a thermoelectric conversion element.

[0035] Figure 10 It is a view showing an example of the measurement result of the resistance of a thermoelectric conversion element according to Example 1.

[0036] Figure 11A It is a photograph of a cross-section of a thermoelectric conversion element according to Example 1 obtained by using a scanning transmission electron microscope and energy dispersive X-ray spectroscopy (SEM-EDX).

[0037] Figure 11B It is a photograph of a cross-section of a thermoelectric conversion element according to Example 1 obtained by using SEM-EDX.

[0038] Figure 12 It is a photograph of a cross-section of a thermoelectric conversion element according to Comparative Example 1 obtained by using SEM-EDX.

[0039] Figure 13 It is a photograph showing the peeling of a coating film in Comparative Example 3. Detailed implementation manners

[0040] (Insights underlying the present disclosure)

[0041] It is possible to form a metal layer by methods such as electrolytic plating and electroless plating. When the physical adhesion at the interface between the material to be plated and the plating material is low, the interface resistivity at this interface may become high. The same applies to techniques for forming a metal layer other than plating, such as spraying.

[0042] According to the research of the present inventor: For example, when a metal layer containing a metal such as Cu is formed by plating or the like on a layer containing a thermoelectric conversion material containing Mg, the interface resistivity between the layer containing the thermoelectric conversion material and the metal layer tends to become high. According to further research by the present inventor, it is speculated that ceramic particles considered to be derived from abrasive grains used for cutting and grinding are embedded in the cut surface and polished surface of the layer containing the thermoelectric conversion material, thereby increasing the interface resistivity.

[0043] According to Patent Documents 1, 2, and 3, several materials are described as the metal layer in contact with the layer containing the thermoelectric conversion material containing Mg. However, no research has been conducted on the influence of abrasive grains.

[0044] According to Patent Document 4, it is understood that a polycrystalline magnesium silicide-based thermoelectric conversion material having silicon carbide in the crystal grains has high mechanical strength. However, no research has been conducted on the influence of the presence of ceramic particles in the cut surface and polished surface of the layer containing the thermoelectric conversion material on the interface resistivity.

[0045] According to Patent Document 5, it is understood that this thermoelectric conversion material has high mechanical strength by containing a predetermined non-oxide ceramic particle in the sintered body. However, no research has been conducted on the influence of the presence of ceramic particles in the cut surface and polished surface of the layer containing the thermoelectric conversion material on the interface resistivity.

[0046] Therefore, in order to solve the above problems in the case of forming a metal layer in contact with a layer containing a thermoelectric conversion material containing Mg, the present inventor repeatedly conducted a large number of exploratory experiments. As a result, it was newly found that by performing a specific treatment after forming a metal layer in contact with a layer containing a thermoelectric conversion material containing Mg, the relationship between the ceramic particles derived from abrasive grains and the metal layer is adjusted to a specified state. In addition, it was newly found that thereby, the interface resistivity between the layer containing the thermoelectric conversion material and the metal layer can be reduced. Based on this new insight, the present inventor completed the thermoelectric conversion element related to the present disclosure.

[0047] (Embodiments of the present disclosure)

[0048] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0049] (Embodiment 1)

[0050] Figure 1AIt is a cross-sectional view schematically showing an example of the thermoelectric conversion element of Embodiment 1. As Figure 1A shown, the thermoelectric conversion element 10a includes a first metal layer 12a, a second metal layer 12b, and a thermoelectric conversion layer 11. The thermoelectric conversion layer 11 is disposed between the first metal layer 12a and the second metal layer 12b in the thickness direction of the first metal layer 12a. The thermoelectric conversion layer 11 contains a thermoelectric conversion material containing Mg. The first metal layer 12a contains ceramic particles 12p. The ceramic particles 12p are disposed inside the first metal layer 12a. In other words, the ceramic particles 12p exist at a position away from the boundary between the first metal layer 12a and the outside of the first metal layer 12a. For example, the ceramic particles 12p do not contact the thermoelectric conversion layer 11 and exist at a position away from the thermoelectric conversion layer 11.

[0051] By disposing the ceramic particles 12p inside the first metal layer 12a, the interfacial resistivity at the interface between the first metal layer 12a and the outside of the first metal layer 12a is likely to be lowered. Therefore, the resistance of the thermoelectric conversion element 10a is likely to be lowered.

[0052] The thermoelectric conversion layer 11 has, for example, a first end 11a and a second end 11b in the thickness direction of the first metal layer 12a. For example, the first metal layer 12a contacts the first end 11a. In this case, by including the ceramic particles 12p inside the first metal layer 12a, the interfacial resistance at the interface between the first metal layer 12a and the thermoelectric conversion layer 11 is likely to be lowered. For example, the second metal layer 12b contacts the second end 11b.

[0053] The second metal layer 12b is formed in the same manner as the first metal layer 12a, for example, and the ceramic particles 12p may also be included inside the second metal layer 12b. The description of the first metal layer 12a also applies to the second metal layer 12b as long as there is no technical contradiction. As Figure 1A shown, for example, the ceramic particles 12p may be included inside each of the first metal layer 12a and the second metal layer 12b.

[0054] The ceramic particles 12p may be included only in the first metal layer 12a in the thermoelectric conversion element 10a, or may be included in both the first metal layer 12a and the second metal layer 12b.

[0055] The ceramic particles 12p are not limited to specific ceramic particles. The ceramic particles 12p are, for example, non-metallic inorganic particles. The ceramic particles 12p can be particles made of a material composed of non-metallic elements including silicon and diamond, or can be particles containing inorganic compounds such as metal oxides, metal carbides, and metal nitrides. The ceramic particles 12p can be fired or can not be fired. The ceramic particles 12p are, for example, derived from abrasive grains or tools used for grinding and cutting of thermoelectric conversion materials. The ceramic particles 12p are, for example, ceramic particles. The ceramic particles 12p can also contain alumina. The ceramic particles 12p can also contain at least one selected from SiC and SiO2.

[0056] The presence of the ceramic particles 12p can be confirmed, for example, by observing a cross-section in the thickness direction of the first metal layer 12a using a scanning electron microscope method and an energy dispersive X-ray spectroscopy (SEM-EDX). By sputtering using Ar ions, a clean surface is formed on the thermoelectric conversion element 10a that includes the interface between the first metal layer 12a or the second metal layer 12b and the thermoelectric conversion layer 11 and is perpendicular to the interface. SEM-EDX is performed on this clean surface.

[0057] The size of the ceramic particles 12p is not limited to a specific value. A cross-section in the thickness direction of the first metal layer 12a is observed using a scanning electron microscope method and an energy dispersive X-ray spectroscopy (SEM-EDX). In this case, the ceramic particles 12p satisfy, for example, the condition expressed by 0.5 μm ≤ d. In this condition, d is the maximum size of the ceramic particles 12p. For example, the maximum size d of the ceramic particles 12p can be determined using an elemental mapping image of the cross-section in the thickness direction of the first metal layer 12a.

[0058] In the above cross-section, the maximum size d of the ceramic particles 12p satisfies, for example, a second condition expressed by d ≤ 10 μm.

[0059] The metals contained in the first metal layer 12a and the second metal layer 12b are not limited to specific metals. The first metal layer 12a and the second metal layer 12b can contain Cu and can contain Ni.

[0060] As Figure 1A shown, the first metal layer 12a further includes an electrode layer 12m and an intermediate layer 12n. The electrode layer 12m contains Cu. The intermediate layer 12n is disposed between the electrode layer 12m and the thermoelectric conversion layer 11 in the thickness direction of the first metal layer 12a. The intermediate layer 12n contains Mg and Cu.

[0061] The ceramic particles 12p are arranged in the first metal layer 12a in at least one selected from the following (a), (b), and (c). In this case, the interfacial resistivity at the interface between the first metal layer 12a and the outside of the first metal layer 12a is likely to become lower, and the resistance of the thermoelectric conversion element 10a is likely to become lower.

[0062] (a) Inside the electrode layer 12m

[0063] (b) Inside the intermediate layer 12n

[0064] (c) The boundary region between the electrode layer 12m and the intermediate layer 12n

[0065] The intermediate layer 12n is formed, for example, as a diffusion layer. The intermediate layer 12n is formed, for example, by the diffusion of Mg derived from the raw material of the thermoelectric conversion layer 11 in the first metal layer 12a or the second metal layer 12b.

[0066] As Figure 1A shown, the electrode layer 12m is in contact with the intermediate layer 12n, for example. The electrode layer 12m may be separated from the intermediate layer 12n in the thickness direction of the first metal layer 12a. Regarding the above (c), when the electrode layer 12m is in contact with the intermediate layer 12n, the boundary region includes their boundary line. When the electrode layer 12m and the intermediate layer 12n are separated in the thickness direction of the first metal layer 12a, the boundary region includes the region between these layers.

[0067] As Figure 1A shown, the second metal layer 12b further includes an electrode layer 12m and an intermediate layer 12n in the same manner as the first metal layer 12a. In the second metal layer 12b, the intermediate layer 12n is arranged between the electrode layer 12m and the thermoelectric conversion layer 11 in the thickness direction of the second metal layer 12b. In this case, the ceramic particles 12p in the second metal layer 12b can be arranged in at least one selected from the above (a), (b), and (c).

[0068] When the ceramic particles 12p are included in both the first metal layer 12a and the second metal layer 12b, the arrangement of the ceramic particles 12p in each of the first metal layer 12a and the second metal layer 12b may be the same or different.

[0069] For example, as Figure 1A shown, in the first metal layer 12a, the ceramic particles 12p exist across the inside of the electrode layer 12m, the inside of the intermediate layer 12n, and the boundary between the electrode layer 12m and the intermediate layer 12n. In the second metal layer 12b, the ceramic particles 12p exist only inside the intermediate layer 12n.

[0070] Figure 1Bis a cross-sectional view schematically showing another example of the thermoelectric conversion element 10a. As Figure 1B shown, in each of the first metal layer 12a and the second metal layer 12b, the ceramic particles 12p may also exist across the inside of the electrode layer 12m, the inside of the intermediate layer 12n, and the boundary between the electrode layer 12m and the intermediate layer 12n.

[0071] Figure 1C is a cross-sectional view schematically showing yet another example of the thermoelectric conversion element. As Figure 1C shown, in each of the first metal layer 12a and the second metal layer 12b, the ceramic particles 12p may also exist only inside the intermediate layer 12n.

[0072] Figure 1D 、 Figure 1E and Figure 1F are cross-sectional views schematically showing yet another example of the thermoelectric conversion element, respectively. As described above, in the thermoelectric conversion element 10a, the ceramic particles 12p may also be contained only in the first metal layer 12a. In this case, for example, as Figure 1D shown, the ceramic particles 12p may also exist across the inside of the electrode layer 12m, the inside of the intermediate layer 12n, and the boundary between the electrode layer 12m and the intermediate layer 12n. As Figure 1E shown, the ceramic particles 12p may also exist only inside the intermediate layer 12n. As Figure 1F shown, the ceramic particles 12p existing across the inside of the electrode layer 12m, the inside of the intermediate layer 12n, and the boundary between the electrode layer 12m and the intermediate layer 12n and the ceramic particles 12p existing only inside the intermediate layer 12n may be mixed.

[0073] As described above, the ceramic particles 12p may also be arranged in the intermediate layer 12n. In this case, the first metal layer 12a or the second metal layer 12b may also satisfy the condition represented by 0.1 ≤ d / A ≤ 10. In this case, the interfacial resistivity at the interface between the first metal layer 12a and the outside of the first metal layer 12a is likely to become lower, and the resistance of the thermoelectric conversion element 10a is likely to become lower. d is the maximum size of the ceramic particles 12p when observing a cross-section in the thickness direction of the first metal layer 12a or the second metal layer 12b by SEM-EDX. A is the thickness of the intermediate layer 12n.

[0074] The shape of the thermoelectric conversion element 10a is not limited to a specific shape. The thermoelectric conversion element 10a is, for example, substantially rectangular parallelepiped-shaped. The shape of the thermoelectric conversion element 10a may be any shape as long as it can form the thermoelectric conversion layer 11 containing the thermoelectric conversion material, and may be, for example, rectangular parallelepiped-shaped, cubic-shaped, substantially cubic-shaped, other polygonal prism-shaped, substantially polygonal prism-shaped, cylindrical-shaped, or tubular-shaped.

[0075] The thickness of the thermoelectric conversion layer 11 is not limited to a specific value. For example, its thickness is 0.1 mm or more and 5.0 mm or less. The thickness of the thermoelectric conversion layer 11 can also be adjusted to a specified range by dry-grinding a member containing a thermoelectric conversion material, for example. The thickness of the thermoelectric conversion layer 11 can also be adjusted to a specified range by dividing a member containing a thermoelectric conversion material into a plurality of pieces using a wire saw or a blade saw. The thickness of the thermoelectric conversion layer 11 can also be adjusted to a specified range by combining dry-grinding with the use of a wire saw and a blade saw.

[0076] The thermoelectric conversion material contained in the thermoelectric conversion layer 11 is not limited to a specific material as long as it contains Mg. The thermoelectric conversion material further contains, for example, at least one selected from Sb and Bi. In this case, the thermoelectric conversion element 10a easily exhibits the desired thermoelectric conversion characteristics. The thermoelectric conversion material is, for example, an N-type thermoelectric conversion material. The thermoelectric conversion material may further contain Si and may be a magnesium silicide-based thermoelectric conversion material.

[0077] The thermoelectric conversion material contained in the thermoelectric conversion layer 11 has, for example, a La2O3-type crystal structure. In this case, the thermoelectric conversion element 10a more easily exhibits the desired thermoelectric conversion characteristics. Whether the thermoelectric conversion material has a La2O3-type crystal structure can be determined, for example, based on the X-ray diffraction measurement results of a specimen of the thermoelectric conversion material. Figure 2 is a diagram schematically showing the La2O3-type crystal structure. When the thermoelectric conversion material has a La2O3-type crystal structure, for example, Mg is located at Figure 2 the C1 site shown, and at least one selected from Sb and Bi is located at the C2 site. As Figure 2 shown, a bond as indicated by a dotted line is formed between the C1 site and the C2 site.

[0078] The thermoelectric conversion material further contains Te, for example. In this case, the thermoelectric conversion element 10a more easily exhibits the desired thermoelectric conversion characteristics.

[0079] The thermoelectric conversion material has, for example, Mg 3+m R a T b Sb 2-e-c Bi c Z eThe composition shown. In this composition, element R is at least one element selected from Ca, Sr, Ba, and Yb. Element T is at least one element selected from Mn and Zn. Element Z is at least one element selected from Te, Se, Sc, Y, and La. The value of m satisfies -0.39 ≤ m ≤ 0.42. The value of a satisfies 0 ≤ a ≤ 0.12. The value of b satisfies 0 ≤ b ≤ 0.48. The value of c satisfies 0 ≤ c ≤ 1.6. The value of e satisfies 0.001 ≤ e ≤ 0.06. In this case, the thermoelectric conversion element 10a is more likely to exhibit the desired thermoelectric conversion characteristics.

[0080] In the first metal layer 12a and the second metal layer 12b, the thickness of the electrode layer 12m is not limited to a specific value. The thickness of the electrode layer 12m is, for example, 0.5 μm or more and 100 μm or less, preferably 0.5 μm or more and 10 μm or less. In the first metal layer 12a and the second metal layer 12b, the thickness of the intermediate layer 12n is not limited to a specific value. The thickness of the intermediate layer 12n is, for example, 0.01 μm or more and 100 μm or less, preferably 0.01 μm or more and 50 μm or less. In the first metal layer 12a and the second metal layer 12b, the thickness of the electrode layer 12m and the thickness of the intermediate layer 12n may be the same or different.

[0081] The electrode layer 12m contains, for example, Cu or an alloy containing Cu. The intermediate layer 12n is, for example, a diffusion layer, and may also be a layer formed by the diffusion of metals from the raw materials of the electrode layer 12m and the thermoelectric conversion layer 11. The intermediate layer 12n contains an alloy containing Cu. Examples of the alloy containing Cu are alloys containing Cu and at least one selected from Mg, Sb, Bi, Te, and Zn. For example, at least one selected from Mg, Sb, Bi, Te, and Zn from the raw materials of the thermoelectric conversion layer 11 diffuses in the first metal layer 12a or the second metal layer 12b and alloyizes with Cu.

[0082] The thermoelectric conversion element 10a may also have another layer such as an electrode layer on the surface that does not contact the first end 11a or the second end 11b in the thickness direction of the first metal layer 12a or the second metal layer 12b for the purpose of bonding to a circuit and preventing oxidation of the electrode, etc. The other layer may be a single layer or a multilayer. An example of the other layer is a layer having a structure in which a Ni layer and an Au layer are sequentially formed on the first metal layer 12a or the second metal layer 12b in the thickness direction of the first metal layer 12a or the second metal layer 12b. In the layers formed on the first metal layer 12a and the second metal layer 12b, the composition of the material, the layer structure, and the thickness of each layer may be the same or different. A diffusion layer may or may not exist between the layers.

[0083] The thermoelectric conversion element 10a can be manufactured, for example, by subjecting a laminate including a precursor of the thermoelectric conversion layer 11, a precursor of the metal layer formed in contact with the precursor of the thermoelectric conversion layer 11, and the ceramic particles 12p to a specific treatment including heating the laminate. The ceramic particles 12p are in contact with the precursor of the thermoelectric conversion layer 11 in the laminate. The ceramic particles 12p are in contact with the precursor of the thermoelectric conversion layer 11 obtained, for example, by cutting the thermoelectric conversion material. In addition, the ceramic particles 12p are in contact with the precursor of the thermoelectric conversion layer 11 obtained, for example, by grinding the thermoelectric conversion material. The precursor of the thermoelectric conversion layer 11 becomes the thermoelectric conversion layer 11, and the precursor of the metal layer becomes the first metal layer 12a or the second metal layer 12b.

[0084] Figure 3 is a flowchart showing the manufacturing method of the thermoelectric conversion element of Embodiment 1. As Figure 3 shown, in step S11, a thermoelectric conversion material is produced. An example of the method for producing the thermoelectric conversion material is shown below. The method for producing the thermoelectric conversion material is not limited to the following method.

[0085] A solid-phase reaction is caused in a state where Mg particles and at least one kind of particles selected from Sb particles and Bi particles are mixed as raw materials, and a powdery alloy containing Mg and at least one of Sb and Bi is obtained. The raw materials may be selected so that the powdery alloy contains metals other than Sb and Bi. In the solid-phase reaction, powders of elements as dopants may be mixed as needed. The raw materials may be particles or powders. An example of the method for causing the solid-phase reaction is mechanical alloying. The alloy may also be obtained by other methods other than the solid-phase reaction, such as a melting method.

[0086] Next, the powdery alloy is sintered to obtain a single crystal or polycrystalline alloy. The sintering of the powdery alloy can be performed, for example, by a spark plasma sintering method or a hot pressing method. The obtained sintered body can be used as the thermoelectric conversion material as it is. The obtained sintered body may also be heat-treated, and the heat-treated sintered body can also be used as the thermoelectric conversion material.

[0087] Next, in step S12, the thickness of the member including the thermoelectric conversion material is adjusted to obtain a precursor of the thermoelectric conversion layer 11 having a prescribed thickness. In adjusting the thickness of the member including the thermoelectric conversion material, dry grinding, wet grinding, wire sawing, or wafer sawing can be used, for example. Abrasive grains can also be used in adjusting the thickness of the member including the thermoelectric conversion material. It is considered that ceramic particles 12p such as those derived from an abrasive are embedded in the precursor of the thermoelectric conversion material layer. For example, particles of ceramics such as alumina and SiC used as abrasive grains in wet grinding, or particles of diamond or the like used in tools such as wire saws and wafer saws can be embedded in the precursor of the thermoelectric conversion layer 11. In addition, a part of other inorganic materials used in abrasive papers, abrasives, wire saws, and wafer saws may be embedded in the precursor of the thermoelectric conversion material layer.

[0088] Next, in step S13, a precursor of the metal layer is formed in contact with the end face of the precursor of the thermoelectric conversion layer 11. The method of forming the precursor of the metal layer is not limited to a specific method. Examples of the method of forming the precursor of the metal layer are electroplating, electroless plating, sputtering, and spraying. When the precursor of the metal layer is formed by electroplating, a commercially available plating solution can also be used. After the plating is completed, a cleaning process for removing the plating solution can be performed.

[0089] Next, in step S14, a specific treatment is performed on the precursor of the metal layer, and the specific treatment includes heating a laminate of the precursor of the thermoelectric conversion layer 11 and the precursor of the metal layer. Thereby, the ceramic particles 12p are disposed inside the first metal layer 12a or the second metal layer 12b. The specific treatment can also be, for example, a treatment including heating the laminate based on the conditions assumed for the use of the thermoelectric conversion element 10a to generate energization. The time of the specific treatment can be set according to the characteristics required for the thermoelectric conversion element 10a. The time of the specific treatment is, for example, 500 hours. In this way, the thermoelectric conversion element 10a can be manufactured. The specific treatment can also be performed after the assembly for manufacturing the thermoelectric conversion module described later. The specific treatment can be performed multiple times. For example, the specific treatment can be performed in both the state of the element before the assembly for manufacturing the thermoelectric conversion module and the state after the assembly for manufacturing the thermoelectric conversion module.

[0090] The specific treatment is performed, for example, in such a manner that the absolute value |ΔY / (Y(t)Δt)| becomes equal to or less than a prescribed value. ΔY is the amount of change in a prescribed characteristic of the element during the period from time t to time t + Δt. Y(t) is the value of the prescribed characteristic of the element at time t. The prescribed characteristic of the element is, for example, the resistance of the element.

[0091] (Embodiment 2)

[0092] Figure 4 This is a cross-sectional view showing an example of the thermoelectric conversion module of Embodiment 2. As Figure 4 shown, the thermoelectric conversion module 100 includes a P-type thermoelectric element 20a, an N-type thermoelectric element as the thermoelectric conversion element 10a, and an electrode 31. The electrode 31 electrically connects one end portion of the P-type thermoelectric conversion element 20a and one end portion of the N-type thermoelectric conversion element 10a. The first metal layer 12a may be directly connected to the electrode 31, or another layer may be disposed between the electrode 31 and the first metal layer 12a.

[0093] As Figure 4 shown, the P-type thermoelectric element 20a includes, for example, a thermoelectric conversion layer 21 and a pair of electrode layers 22. The electrode layer 22 contacts the end face 21a of the thermoelectric conversion layer 21. The end face 21a is the end face of the thermoelectric conversion layer 21 in the thickness direction of the electrode layer 22. The pair of electrode layers 22 contact both end faces of the thermoelectric conversion layer 21 in the thickness direction of the electrode layer 22. The electrode layer 22 may be directly connected to the electrode 31, or another layer may be disposed between the electrode 31 and the electrode layer 22. The connection method of the P-type thermoelectric element 20a to an external electrode may be the same as or different from the connection method of the N-type thermoelectric conversion element 10a to an external electrode.

[0094] The thermoelectric conversion layer 21 contains a P-type thermoelectric conversion material. Examples of the P-type thermoelectric conversion material are bismuth telluride, cesium bismuth telluride, germanium telluride, bismuth antimony, Mg3(Sb, Bi)2, and MgAgSb. (Sb, Bi) means containing at least one selected from Sb and Bi. The N-type thermoelectric conversion material contained in the thermoelectric conversion layer 11 and the P-type thermoelectric conversion material contained in the thermoelectric conversion layer 21 may be materials of the same alloy system or materials of different alloy systems. The same alloy system means that the elements constituting the alloy are the same. From the viewpoint of reducing the thermal stress in the thermoelectric conversion module 100, it is important that the difference in the thermal expansion coefficient between the N-type thermoelectric conversion material contained in the thermoelectric conversion layer 11 and the P-type thermoelectric conversion material contained in the thermoelectric conversion layer 21 is small. For example, when the P-type thermoelectric conversion material is Mg3(Sb, Bi)2 or bismuth telluride, the difference in the thermal expansion coefficient between the N-type thermoelectric conversion material and the P-type thermoelectric conversion material is likely to be small.

[0095] When the P-type thermoelectric conversion material is bismuth telluride, the electrode layer 22 is, for example, a layer such as a Ni plating layer, a Ni spray plating layer, a Ni sputtering layer, or a Mo spray plating layer. When the P-type thermoelectric conversion material is bismuth telluride and is represented by the composition of Bi2Te x x, for example, the x in this composition satisfies the condition of 2 < x < 4. The composition of bismuth telluride may be Bi2Te3. It may also contain at least one selected from antimony and selenium in bismuth telluride. Bismuth telluride containing antimony has, for example, (Bi 1-y Sby )2Te x Composition. In the case where the composition of the P-type thermoelectric conversion material has (Bi 1-y Sb y )2Te x composition, for example, satisfies the condition of 0 < y < 1, and preferably satisfies the condition of 0.6 < y < 0.9.

[0096] Figure 5 is a cross-sectional view showing another example of the thermoelectric conversion module. As Figure 5 shown, the thermoelectric conversion module 200 is configured in the same manner as the thermoelectric conversion module 100, except that the thermoelectric conversion element 10b is provided instead of the thermoelectric conversion element 10a as the N-type thermoelectric conversion element. The thermoelectric conversion element 10b is configured in the same manner as the thermoelectric conversion element 10a, except for the parts specifically described. The components of the thermoelectric conversion element 10b that are the same as or corresponding to the components of the thermoelectric conversion element 10a are marked with the same reference numerals, and detailed descriptions are omitted. The description of the thermoelectric conversion element 10a also applies to the thermoelectric conversion element 10b as long as there is no technical contradiction.

[0097] As Figure 5 shown, the thermoelectric conversion element 10b includes a first metal layer 12a, an electrode layer 13a, an electrode layer 14a, a second metal layer 12b, an electrode layer 13b, and an electrode layer 14b. In the thermoelectric conversion element 10b, the first metal layer 12a, the electrode layer 13a, and the electrode layer 14a are sequentially arranged in the thickness direction of the first metal layer 12a starting from the first end 11a of the thermoelectric conversion layer 11. The thermoelectric conversion layer 11 is electrically connected to the electrode 31 through the first metal layer 12a, the electrode layer 13a, and the electrode layer 14a. In the thermoelectric conversion element 10b, the second metal layer 12b, the electrode layer 13b, and the electrode layer 14b are sequentially arranged in the thickness direction of the second metal layer 12b starting from the second end 11b of the thermoelectric conversion layer 11.

[0098] Figure 6 is a cross-sectional view showing still another example of the thermoelectric conversion module. Figure 6 The thermoelectric conversion module 300 shown is configured in the same manner as the thermoelectric conversion module 100, except for the parts specifically described. As Figure 6As shown, the thermoelectric conversion module 300 further includes an electrode 32 and an electrode 33. The other end of the N-type thermoelectric conversion element 10a is electrically connected to the electrode 32 through the second metal layer 12b. The other end of the P-type thermoelectric conversion element 20a is electrically connected to the electrode 33 through the electrode layer 22. The thermoelectric conversion module 300 also includes a first wiring 41 and a second wiring 42. The first wiring 41 is connected to the electrode 32. The second wiring 42 is connected to the electrode 33. The first wiring 41 and the second wiring 42, for example, are responsible for applying a voltage to the N-type thermoelectric conversion element 10a and the P-type thermoelectric conversion element 20a. The first wiring 41 and the second wiring 42 may also be responsible for supplying the electricity generated in the thermoelectric conversion module 300 to the outside of the thermoelectric conversion module 300.

[0099] (Embodiment 3)

[0100] Figure 7 is a side view showing the thermoelectric conversion system of Embodiment 3. As Figure 7 shown, the thermoelectric conversion system 500 includes a thermoelectric conversion module 400 and a heat source 70. The thermoelectric conversion module 400 is configured in the same manner as the thermoelectric conversion module 100 except for the parts specifically described. The thermoelectric conversion module 400 includes an electrode 31, an electrode 32, and an electrode 33. The heat source 70 is disposed on the side of the electrode 31. The electrode 32 and the electrode 33 electrically connect the other end of the P-type thermoelectric conversion element 20a and the other end of the N-type thermoelectric conversion element 10a.

[0101] The thermoelectric conversion system 500, for example, further includes a pair of substrates 60. One of the pair of substrates 60 is disposed in contact with the electrode 31, and the other of the pair of substrates 60 is disposed in contact with the electrode 32 and the third electrode 33. With such a configuration, in the thermoelectric conversion system 500, it is difficult to generate a temperature deviation in the direction parallel to the main surface of the substrate 60. The material of the substrate 60 is not limited to a specific material. The substrate 60 includes, for example, alumina or aluminum nitride.

[0102] According to the thermoelectric conversion system 500, the following power generation method can be provided, which includes: generating a temperature difference by using the heat from the heat source 70 in the thermoelectric conversion module 400 to generate electricity.

[0103] The thermoelectric conversion elements of the above embodiments can be used, for example, in various applications including those of conventional thermoelectric conversion elements. The thermoelectric conversion modules 100, 200, 300, and 400 can be manufactured by assembling the N-type thermoelectric conversion element 10a or 10b and the P-type thermoelectric conversion element 20a using known methods.

[0104] (Supplementary Note)

[0105] Based on the above description, the following technology is disclosed.

[0106] (Technology 1)

[0107] A thermoelectric conversion element,

[0108] comprising a first metal layer, a second metal layer, and a thermoelectric conversion layer, wherein the thermoelectric conversion layer is disposed between the first metal layer and the second metal layer in the thickness direction of the first metal layer and contains a thermoelectric conversion material, and the thermoelectric conversion material contains Mg,

[0109] The first metal layer contains ceramic particles,

[0110] The ceramic particles are disposed inside the first metal layer.

[0111] (Technology 2)

[0112] The thermoelectric conversion element according to Technology 1, wherein the thermoelectric conversion material further contains at least one selected from Sb and Bi.

[0113] (Technology 3)

[0114] The thermoelectric conversion element according to Technology 1 or 2, wherein the first metal layer further contains an electrode layer and an intermediate layer, the electrode layer contains Cu, and the intermediate layer is disposed between the electrode layer and the thermoelectric conversion layer in the thickness direction of the first metal layer and contains Mg and Cu.

[0115] (Technology 4)

[0116] The thermoelectric conversion element according to Technology 3, wherein the ceramic particles are disposed in at least one of the following (a), (b), and (c).

[0117] (a) Inside the electrode layer

[0118] (b) Inside the intermediate layer

[0119] (c) The boundary region between the electrode layer and the intermediate layer

[0120] (Technology 5)

[0121] The thermoelectric conversion element according to any one of Technologies 1 to 4, wherein the ceramic particles contain alumina.

[0122] (Technology 6)

[0123] The thermoelectric conversion element according to any one of Technologies 1 to 5, wherein the ceramic particles contain at least one selected from SiC and SiO2.

[0124] (Technology 7)

[0125] The thermoelectric conversion element according to any one of Technologies 1 to 6,

[0126] When observing a cross-section in the thickness direction of the first metal layer by means of a scanning electron microscope method and an energy dispersive X-ray spectroscopy method, the ceramic particles satisfy a first condition represented by 0.5 μm ≤ d.

[0127] In the first condition, d is the maximum size of the ceramic particles.

[0128] (Technology 8)

[0129] For the thermoelectric conversion element according to Technology 7, the ceramic particles satisfy a second condition represented by d ≤ 10 μm in the cross-section.

[0130] (Technology 9)

[0131] For the thermoelectric conversion element according to Technology 3,

[0132] the ceramic particles are arranged in the intermediate layer,

[0133] the first metal layer satisfies a third condition represented by 0.1 ≤ d / A ≤ 10,

[0134] In the third condition,

[0135] d is the maximum size of the ceramic particles in a cross-section in the thickness direction of the first metal layer based on the scanning electron microscope method and the energy dispersive X-ray spectroscopy method,

[0136] A is the thickness of the intermediate layer.

[0137] (Technology 10)

[0138] For the thermoelectric conversion element according to any one of Technologies 1 to 9, the thermoelectric conversion material has a crystal structure of the La2O3 type.

[0139] (Technology 11)

[0140] For the thermoelectric conversion element according to any one of Technologies 1 to 10, the thermoelectric conversion material further contains Te.

[0141] (Technology 12)

[0142] For the thermoelectric conversion element according to any one of Technologies 1 to 11,

[0143] the thermoelectric conversion material has a composition represented by Mg 3+m R a T b Sb 2-e-c Bi c Z e and represents,

[0144] In the composition,

[0145] the element R is at least one element selected from Ca, Sr, Ba, and Yb,

[0146] the element T is at least one element selected from Mn and Zn,

[0147] the element Z is at least one element selected from Te, Se, Sc, Y, and La,

[0148] the value of m satisfies -0.39 ≤ m ≤ 0.42,

[0149] the value of a satisfies 0 ≤ a ≤ 0.12,

[0150] the value of b satisfies 0 ≤ b ≤ 0.48,

[0151] the value of c satisfies 0 ≤ c ≤ 1.6,

[0152] the value of e satisfies 0.001 ≤ e ≤ 0.06.

[0153] (Technology 13)

[0154] A thermoelectric conversion module includes:

[0155] a P-type thermoelectric conversion element;

[0156] an N-type thermoelectric conversion element; and

[0157] an electrode that electrically connects one end portion of the P-type thermoelectric conversion element and one end portion of the N-type thermoelectric conversion element,

[0158] The N-type thermoelectric conversion element is the thermoelectric conversion element described in any one of Technologies 1 to 12.

[0159] (Technology 14)

[0160] A thermoelectric conversion system includes the thermoelectric conversion module described in Technology 13 and a heat source disposed on the electrode side.

[0161] (Technology 15)

[0162] A power generation method includes: generating an electric current by generating a temperature difference using heat from a heat source in the thermoelectric conversion module described in Technology 13.

[0163] (Technology 16)

[0164] A method for manufacturing a thermoelectric conversion element includes: subjecting a laminate including a precursor of a thermoelectric conversion layer, a precursor of a metal layer formed in contact with the precursor of the thermoelectric conversion layer, and ceramic particles to a specific treatment including heating the laminate to obtain a thermoelectric conversion element,

[0165] The ceramic particles are in contact with a precursor of the thermoelectric conversion layer in the laminate.

[0166] The thermoelectric conversion layer contains a thermoelectric conversion material, and the thermoelectric conversion material contains Mg.

[0167] In the thermoelectric conversion element, the ceramic particles are disposed inside the metal layer.

[0168] (Technology 17)

[0169] The method for manufacturing a thermoelectric conversion element according to Technology 16 further includes: cutting the thermoelectric conversion material to obtain a precursor of the thermoelectric conversion layer.

[0170] (Technology 18)

[0171] The method for manufacturing a thermoelectric conversion element according to Technology 16 or 17 further includes: grinding the thermoelectric conversion material to obtain a precursor of the thermoelectric conversion layer.

[0172] Examples

[0173] The present disclosure will be described in detail below with reference to examples. However, the thermoelectric conversion element of the present disclosure is not limited to the examples shown below.

[0174] (Example 1)

[0175] Weigh approximately 2.9 g of a powder of an alloy having a composition of Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 produced by solid-phase reaction inside a glove box. The inside of the glove box is maintained in an argon atmosphere until the thermoelectric conversion material is obtained. Next, the weighed powder is filled into the sintering space of a carbon mold, and powder pressing is performed using a carbon punch. The inner diameter of the mold is 10 mm. Next, the mold is placed in the chamber of a spark plasma sintering apparatus. The chamber is maintained in an argon atmosphere. Next, while applying a pressure of 50 MPa to the filler in the mold, an electric current is applied to the mold by the sintering apparatus. By applying the electric current, after the temperature of the mold reaches 840 °C as the sintering temperature, this temperature is maintained for 10 minutes. Then, the electric current flowing through the mold is reduced, and the heating of the mold is stopped. After confirming that the temperature of the mold has dropped to room temperature, the sintered body is taken out from the inside of the mold to obtain the thermoelectric conversion material of Example 1. The surface of the taken-out sintered body, i.e., the thermoelectric conversion material, that is in contact with the inner surface of the mold is ground and then washed with acetone. The thickness of the sintered body of Example 1 is approximately 6.5 mm.

[0176] The sintered body thus prepared was cut with a wire saw along a plane perpendicular to the pressing direction to obtain two sintered bodies each having a thickness of about 2.9 mm. In the cutting of the sintered body with a wire saw, alumina particles were used as abrasive grains. The alumina particles had a particle size of #220. After cutting the sintered body with a wire saw, the sintered body was cleaned with acetone.

[0177] Both end faces of the sintered body having a thickness of about 2.9 mm obtained as described above were electroplated with Cu to form a plating layer. After the plating was completed, the sintered body was cleaned.

[0178] The sintered body formed with the plating layer was processed into a rectangular parallelepiped shape with a wire saw. Thus, in a plane parallel to the plating layer, the sintered body had a square profile with a side length of about 3 mm. In addition, the distance between the plating layers was about 2.9 mm.

[0179] Next, a pair of plating layers formed on both end faces of the sintered body were connected to an external electrode to perform a specific treatment. In the specific treatment, an electric current was passed between the pair of plating layers in a state where a heater block heated to 100 °C was in contact with one plating layer. In addition, an electric current was passed between the pair of plating layers in a state where the heater block heated to 100 °C was in contact with the other plating layer. Thus, the thermoelectric conversion element of Example 1 was obtained. The thermoelectric conversion element of Example 1 included a thermoelectric conversion layer derived from the sintered body and a metal layer derived from the plating layer. The specific treatment was performed until |ΔR / (R(t)Δt)| became 1% / 100 hours or less. ΔR is the change amount of the resistance of the element during the period from time t to time t + Δt. R(t) is the resistance of the element at time t. Figure 8 is a photograph showing the thermoelectric conversion element of Example 1. In Figure 8 M1 represents the thermoelectric conversion layer and M2 represents the metal layer.

[0180] The interfacial resistivity at the interface between the thermoelectric conversion layer and the metal layer in the thermoelectric conversion element of Example 1 was obtained as follows. Figure 9 is a diagram schematically showing a method for measuring the resistance of the thermoelectric conversion element. As Figure 9 shown, a pair of external electrodes 71 were mounted on the thermoelectric conversion element 10a. A galvanometer 84 was electrically connected to both of the pair of electrodes 71 through a wire 85. A voltmeter 81 was connected to one external electrode 71 through a wire 82, and a probe 83 was connected to the end of the wire 82 on the side opposite to the one external electrode 71. While moving the probe 83 from one external electrode 71 to the other external electrode 71 at 50-μm intervals in the direction shown by the arrow J, the resistance was measured by a four-terminal measurement method. A source meter (model: 2400) manufactured by KEITHLEY was used in the measurement of the resistance. Figure 10This is a figure showing an example of the measurement results of the resistance of the thermoelectric conversion element of Example 1. Figure 10 In Figure 10 , “A” corresponds to the part corresponding to the first metal layer 12a and one external electrode 71. “B” corresponds to the part corresponding to the thermoelectric material layer 11. “C” corresponds to the part corresponding to the second metal layer 12b and the other external electrode 71. The change amount of the resistance at the boundary between A and B corresponds to the interface resistance at the interface between the thermoelectric conversion layer and the first metal layer. The interface resistivity at the interface between the thermoelectric conversion layer and the metal layer in the thermoelectric conversion element of Example 1 is obtained from the cross-sectional area parallel to the metal layer of the thermoelectric conversion element of Example 1 and the above-mentioned interface resistance. As a result, the interface resistivity is 1.92 mΩ·mm 2 .

[0181] Next, argon ion milling was performed in a direction perpendicular to the interface between the thermoelectric conversion layer and the metal layer of the thermoelectric conversion element of Example 1 to form a smooth cross-section including the interface between the thermoelectric conversion layer and the metal layer. For this smooth cross-section, compositional analysis based on SEM-EDX was performed using a field emission type scanning electron microscope (FE-SEM) SU8220 manufactured by Hitachi High-Tech Corporation and an EDX device FlatQUAD manufactured by Bruker AXS Corporation. The results are shown in Figure 11A and Figure 11B . Figure 11A and Figure 11B are photos of the cross-section of the thermoelectric conversion element of Example 1 obtained by SEM-EDX. In Figure 11A and Figure 11B , the part corresponding to “T” is the thermoelectric conversion layer, the part corresponding to “M1” is the intermediate layer, and the part corresponding to “M2” is the electrode layer. In other words, the metal layer includes the intermediate layer M1 and the electrode layer M2. The intermediate layer M1 contains Cu and Mg and is considered to be a diffusion layer. In the field of view shown in Figure 11A , as shown by the white arrow, alumina particles exist inside the intermediate layer M1. In Figure 11BIn the field of view shown, as indicated by the white arrow, alumina particles exist across the intermediate layer M1 and the electrode layer M2. According to the elemental mapping image of the cross-section of the thermoelectric conversion element based on SEM-EDX, the alumina particles have a maximum size of, for example, 2.5 μm. Additionally, according to the line scan composition analysis of SEM-EDX, the full width at half maximum of the peak derived from the alumina particles is 1.0 μm. As a result of performing the same measurement at other positions, according to the elemental mapping image of the cross-section of the thermoelectric conversion element based on SEM-EDX, the alumina particles have a maximum size of, for example, 0.5 μm to 10 μm. On the other hand, according to the line scan composition analysis of SEM-EDX, the full width at half maximum of the peak derived from the alumina particles is 0.1 μm to 5 μm. The thickness of the intermediate layer M1 is, for example, 2 μm, and at other positions it is 1 μm to 5 μm. In other words, the size of the alumina particles is 0.1 times to 10 times the thickness of the intermediate layer.

[0182] (Examples 2 to 12)

[0183] Except for using the alloy powder having the composition shown in Table 1, the same procedure as in Example 1 was carried out to obtain the thermoelectric conversion elements of Examples 2 to 12. The thermoelectric conversion elements of Examples 2 to 12 were evaluated in the same manner as the thermoelectric conversion element of Example 1. The interfacial resistivity at the interface between the thermoelectric conversion layer and the metal layer in the thermoelectric conversion elements of Examples 2 to 12 is shown in Table 1. According to the results of SEM-EDX for the cross-section of the thermoelectric conversion element, alumina particles exist inside the metal layer (first metal layer).

[0184] (Example 13)

[0185] Except for using SiC as the abrasive grain in the cutting of the sintered body, the same procedure as in Example 1 was carried out to obtain the thermoelectric conversion element of Example 13. The thermoelectric conversion element of Example 13 was evaluated in the same manner as the thermoelectric conversion element of Example 1. The interfacial resistivity at the interface between the thermoelectric conversion layer and the metal layer in the thermoelectric conversion element of Example 13 is shown in Table 1. According to the results of SEM-EDX for the cross-section of the thermoelectric conversion element, SiC particles exist inside the metal layer (first metal layer).

[0186] (Example 14)

[0187] Except for using SiO2 as the abrasive grain in the cutting of the sintered body, the same procedure as in Example 1 was carried out to obtain the thermoelectric conversion element of Example 14. The thermoelectric conversion element of Example 14 was evaluated in the same manner as the thermoelectric conversion element of Example 1. The interfacial resistivity at the interface between the thermoelectric conversion layer and the metal layer in the thermoelectric conversion element of Example 14 is shown in Table 1. According to the results of SEM-EDX for the cross-section of the thermoelectric conversion element, SiO2 particles exist inside the metal layer (first metal layer).

[0188] (Comparative Example 1)

[0189] A thermoelectric conversion element of Comparative Example 1 was obtained in the same manner as in Example 1, except that no specific treatment was performed.

[0190] The thermoelectric conversion element of Comparative Example 1 was evaluated in the same manner as the thermoelectric conversion element of Example 1. The interfacial resistivity at the interface between the thermoelectric conversion layer and the metal layer in the thermoelectric conversion element of Comparative Example 1 is shown in Table 1. Figure 12 is a photograph of the cross-section of the thermoelectric conversion element of Comparative Example 1 obtained by SEM-EDX. As Figure 12 shown by the white arrow in, it can be seen that alumina particles are in direct contact with the thermoelectric conversion layer at the interface between the thermoelectric conversion layer and the metal layer.

[0191] (Comparative Example 2)

[0192] As the powder of the alloy, powder of an alloy having a composition of Mg 3.2 Sb 1.0 Bi 0.99 Te 0.01 was used, and except for this, it was carried out in the same manner as in Comparative Example 1 to obtain a thermoelectric conversion element of Comparative Example 2. The thermoelectric conversion element of Comparative Example 2 was evaluated in the same manner as the thermoelectric conversion element of Example 1. The interfacial resistivity at the interface between the thermoelectric conversion layer and the metal layer in the thermoelectric conversion element of Comparative Example 2 is shown in Table 1. From the results of SEM-EDX of the cross-section of the thermoelectric conversion element, it can be seen that alumina particles are in direct contact with the thermoelectric conversion layer at the interface between the thermoelectric conversion layer and the metal layer.

[0193] (Comparative Example 3)

[0194] Except that alumina particles having a particle size of #36 were used as abrasive grains in the cutting of the sintered body, the cutting of the sintered body was carried out in the same manner as in Comparative Example 1. Cu was electroplated on both end faces of the sintered body obtained after cutting. However, the plating peeled off and a thermoelectric conversion element could not be fabricated. Figure 13 is a photograph showing the peeling of the plating in Comparative Example 3.

[0195] As shown in Table 1, the interfacial resistivity at the interface between the thermoelectric conversion layer and the metal layer in the thermoelectric conversion elements of the respective examples is lower than the interfacial resistivity at the interface between the thermoelectric conversion layer and the metal layer in the thermoelectric conversion elements of Comparative Examples 1 and 2. It is revealed that: by the presence of particles derived from the abrasive grains inside the metal layer, the interfacial resistivity at the interface between the thermoelectric conversion layer and the metal layer becomes lower, which is advantageous from the viewpoint of reducing the resistance of the thermoelectric conversion element.

[0196] Table 1

[0197]

[0198] The thermoelectric conversion element of the present disclosure can be used in various applications including those of conventional thermoelectric conversion elements.

[0199] Explanation of reference numerals

[0200] 10a, 10b Thermoelectric conversion element

[0201] 11 Thermoelectric conversion layer

[0202] 12a First metal layer

[0203] 12b Second metal layer

[0204] 12m Electrode layer

[0205] 12n Intermediate layer

[0206] 12p Ceramic particles

[0207] 20a P-type thermoelectric conversion element

[0208] 31 Electrode

[0209] 70 Heat source

[0210] 100, 200, 300, 400 Thermoelectric conversion module

[0211] 500 Thermoelectric conversion system

Claims

1. A thermoelectric conversion element, comprising a first metal layer, a second metal layer, and a thermoelectric conversion layer. The thermoelectric conversion layer is disposed between the first metal layer and the second metal layer in the thickness direction of the first metal layer and contains a thermoelectric conversion material, and the thermoelectric conversion material contains Mg. The first metal layer contains ceramic particles. The ceramic particles are disposed inside the first metal layer.

2. The thermoelectric conversion element according to claim 1, wherein the thermoelectric conversion material further contains at least one selected from Sb and Bi.

3. The thermoelectric conversion element according to claim 1, wherein the first metal layer further comprises an electrode layer and an intermediate layer. The electrode layer contains Cu, and the intermediate layer is disposed between the electrode layer and the thermoelectric conversion layer in the thickness direction of the first metal layer and contains Mg and Cu.

4. The thermoelectric conversion element according to claim 3, wherein the ceramic particles are disposed in at least one of the following (a), (b), and (c). (a) Inside the electrode layer; (b) Inside the intermediate layer; (c) The boundary region between the electrode layer and the intermediate layer.

5. The thermoelectric conversion element according to claim 1, wherein the ceramic particles contain alumina.

6. The thermoelectric conversion element according to claim 1, wherein the ceramic particles contain at least one selected from SiC and SiO2.

7. The thermoelectric conversion element according to claim 1, when observing a cross-section in the thickness direction of the first metal layer by scanning electron microscopy and energy-dispersive X-ray spectroscopy, the ceramic particles satisfy a first condition represented by 0.5μm ≤ d, under the first condition, d is the maximum size of the ceramic particles.

8. The thermoelectric conversion element according to claim 7, wherein the ceramic particles satisfy a second condition represented by d ≤ 10μm in the cross-section.

9. The thermoelectric conversion element according to claim 3, the ceramic particles are disposed in the intermediate layer, the first metal layer satisfies a third condition represented by 0.1 ≤ d / A ≤ 10, under the third condition, d is the maximum size of the ceramic particles in the cross-section in the thickness direction of the first metal layer based on scanning electron microscopy and energy-dispersive X-ray spectroscopy, A is the thickness of the intermediate layer.

10. The thermoelectric conversion element according to claim 1, wherein the thermoelectric conversion material has a crystal structure of La2O3 type.

11. The thermoelectric conversion element according to claim 1, wherein the thermoelectric conversion material further contains Te.

12. The thermoelectric conversion element according to claim 1, The thermoelectric conversion material has a composition represented by Mg 3+m R a T b Sb 2-e-c Bi c Z e and is represented by in the composition, element R is at least one element selected from Ca, Sr, Ba, and Yb, element T is at least one element selected from Mn and Zn, element Z is at least one element selected from Te, Se, Sc, Y, and La, the value of m satisfies -0.39 ≤ m ≤ 0.42, the value of a satisfies 0 ≤ a ≤ 0.12, the value of b satisfies 0 ≤ b ≤ 0.48, the value of c satisfies 0 ≤ c ≤ 1.6, the value of e satisfies 0.001 ≤ e ≤ 0.

06.

13. A thermoelectric conversion module, comprising: A P-type thermoelectric conversion element; An N-type thermoelectric conversion element; and An electrode that electrically connects one end portion of the P-type thermoelectric conversion element and one end portion of the N-type thermoelectric conversion element, The N-type thermoelectric conversion element is the thermoelectric conversion element described in claim 1.

14. A thermoelectric conversion system, comprising the thermoelectric conversion module described in claim 13 and a heat source disposed on the electrode side.

15. A power generation method, comprising: generating an electric current by using heat from a heat source to generate a temperature difference in the thermoelectric conversion module described in claim 13.

16. A method for manufacturing a thermoelectric conversion element, comprising: subjecting a laminate including a precursor of a thermoelectric conversion layer, a precursor of a metal layer formed in contact with the precursor of the thermoelectric conversion layer, and ceramic particles to a specific treatment including heating the laminate to obtain a thermoelectric conversion element, The ceramic particles are in contact with the precursor of the thermoelectric conversion layer in the laminate, The thermoelectric conversion layer includes a thermoelectric conversion material containing Mg, The ceramic particles are disposed inside the metal layer in the thermoelectric conversion element.

17. The method for manufacturing a thermoelectric conversion element according to claim 16, further comprising: cutting the thermoelectric conversion material to obtain the precursor of the thermoelectric conversion layer.

18. The method for manufacturing a thermoelectric conversion element according to claim 16, further comprising: grinding the thermoelectric conversion material to obtain the precursor of the thermoelectric conversion layer.

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