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). 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) includes a first region (12j) containing oxygen atoms and a second region (12k) other than the first region (12j). The content of oxygen atoms in the first region (12j) on the basis of the number of atoms is higher than the content of oxygen atoms in the second region (12k) of the first metal layer (12a) on the basis of the number of atoms. The content of oxygen atoms in the first region (12j) on the basis of the number of atoms is higher than the content of oxygen atoms in the thermoelectric conversion layer (11) on the basis of the number of atoms.

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] Thermoelectric conversion elements have been known in the past. For example, a thermoelectric conversion module can be provided by electrically connecting an N-type thermoelectric conversion element including an N-type thermoelectric conversion material and a P-type thermoelectric conversion element including a P-type thermoelectric conversion material. In order to facilitate 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.

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

[0004] Patent Document 2 describes a magnesium antimonide-based thermoelectric element. The thermoelectric element includes: a magnesium antimonide-based thermoelectric material matrix layer located at the center of the thermoelectric element; transition layers attached to both surfaces of the matrix layer; and electrode layers attached to the surfaces of the two transition layers. The material of the transition layer is titanium copper alloy or 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 an MgAlB 14 series n-type thermoelectric material. The thermoelectric material contains an oxide phase.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Specification of Chinese Patent No. 111613715

[0010] Patent Document 2: Specification of Chinese Patent No. 110635020

[0011] Patent Document 3: International Publication No. 2020 / 003554

[0012] Patent Document 4: Japanese Unexamined Patent Application Publication No. 2013-211370 Summary of the Invention

[0013] 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.

[0014] The thermoelectric conversion element of the present disclosure

[0015] 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 that contains Mg.

[0016] The first metal layer includes a first region disposed inside the first metal layer and containing oxygen atoms, and a second region other than the first region.

[0017] The content rate of oxygen atoms in the first region based on the number of atoms is higher than the content rate of oxygen atoms in the second region of the first metal layer based on the number of atoms, and higher than the content rate of oxygen atoms in the thermoelectric conversion layer based on the number of atoms.

[0018] 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

[0019] Figure 1A is a cross-sectional view schematically showing an example of the thermoelectric conversion element of Embodiment 1.

[0020] Figure 1B is a cross-sectional view schematically showing another example of the thermoelectric conversion element.

[0021] Figure 1C is a cross-sectional view schematically showing still another example of the thermoelectric conversion element.

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

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

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

[0025] Figure 2 is a diagram schematically showing a La2O3-type crystal structure.

[0026] Figure 3 is a flowchart showing a method for manufacturing a thermoelectric conversion element according to Embodiment 1.

[0027] Figure 4 is a cross-sectional view showing an example of a thermoelectric conversion module according to Embodiment 2.

[0028] Figure 5 is a cross-sectional view showing another example of a thermoelectric conversion module according to Embodiment 2.

[0029] Figure 6 is a cross-sectional view showing still another example of a thermoelectric conversion module according to Embodiment 2.

[0030] Figure 7 is a side view showing a thermoelectric conversion system according to Embodiment 3.

[0031] Figure 8 is a photograph of a thermoelectric conversion element according to Example 1.

[0032] Figure 9 is a diagram schematically showing a method for measuring the resistance of a thermoelectric conversion element.

[0033] Figure 10 is a diagram showing an example of the measurement result of the resistance of a thermoelectric conversion element according to Example 1.

[0034] Figure 11 is a diagram showing a concentration profile based on the number of atoms obtained by performing line composition analysis on a cross-section of a thermoelectric conversion element according to Example 1 by Auger electron spectroscopy (AES).

[0035] Figure 12 is a photograph of a cross-section of a thermoelectric conversion element according to Example 1 obtained by scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy.

[0036] Figure 13A shows Figure 12 a diagram showing the distribution of oxygen atoms in the field of view of the photograph shown.

[0037] Figure 13B shows Figure 12 a diagram showing the distribution of copper atoms in the field of view of the photograph shown. Detailed Embodiments

[0038] (Insight underlying the present disclosure)

[0039] It is conceivable to form a metal layer by methods such as electrolytic plating and electroless plating. If an oxide having a high resistance exists at the interface between the material to be plated and the plating material, the resistance of the entire system may become high. The same can be said for techniques for forming a metal layer other than plating, such as spraying.

[0040] According to the research findings of the present inventors: For example, when a metal layer containing a metal such as Cu is formed on a layer containing a thermoelectric conversion material containing Mg by a method such as plating, the interfacial resistivity between the layer containing the thermoelectric conversion material and the metal layer tends to be high. According to further research by the present inventors, a layer containing an oxide is observed between the layer containing the thermoelectric conversion material and the metal layer, and it is speculated that this layer increases the interfacial resistivity.

[0041] 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, there is no description of the existence of an oxygen-containing region near the interface between the layer containing the thermoelectric conversion material and the metal layer. Patent Document 4 describes that the thermoelectric conversion material containing Mg itself contains an oxide phase. However, there is no description regarding the existence of an oxide at the interface between the layer containing the thermoelectric conversion material and the metal layer.

[0042] 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 inventors repeatedly conducted a large number of exploratory experiments. As a result, it was newly discovered that by performing a specific treatment after forming a metal layer in contact with a thermoelectric conversion layer containing a thermoelectric conversion material containing Mg, the metal layer is adjusted to a prescribed state, and the interfacial resistivity between the layer containing the thermoelectric conversion material and the metal layer can be reduced. Based on this new insight, the present inventors completed the thermoelectric conversion element of the present disclosure.

[0043] (Embodiment of the present disclosure)

[0044] Hereinafter, the embodiments of the present disclosure will be described with reference to the drawings.

[0045] (Embodiment 1)

[0046] Figure 1A is a cross-sectional view schematically showing an example of the thermoelectric conversion element of Embodiment 1. As Figure 1AAs 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 includes a first region 12j containing oxygen atoms and a second region 12k other than the first region 12j. The first region 12j is disposed inside the first metal layer 12a. In other words, the first region 12j exists 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 first region 12j does not contact the thermoelectric conversion layer 11 and exists at a position away from the thermoelectric conversion layer 11. The atomic number-based content rate of oxygen atoms in the first region 12j is higher than the atomic number-based content rate of oxygen atoms in the second region 12k of the first metal layer 12a. In addition, the atomic number-based content rate of oxygen atoms in the first region 12j is higher than the atomic number-based content rate of oxygen atoms in the thermoelectric conversion layer 11.

[0047] By disposing the first region 12j 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 low. Therefore, the resistance of the thermoelectric conversion element 10a is likely to be low.

[0048] The thermoelectric conversion layer 11 has a first end 11a and a second end 11b in the thickness direction of the first metal layer 12a, for example. For example, the first metal layer 12a contacts the first end 11a. In this case, by disposing the first region 12j inside the first metal layer 12a, the interfacial resistivity at the interface between the first metal layer 12a and the thermoelectric conversion layer 11 is likely to be low. For example, the second metal layer 12b contacts the second end 11b.

[0049] The second metal layer 12b is formed in the same manner as the first metal layer 12a, for example, and includes a first region 12j and a second region 12k other than the first region 12j inside the second metal layer 12b. In the second metal layer 12b, the atomic number-based content rate of oxygen atoms in the first region 12j is higher than the atomic number-based content rate of oxygen atoms in the second region 12k of the second metal layer 12b. In addition, the atomic number-based content rate of oxygen atoms in the first region 12j is higher than the atomic number-based content rate of oxygen atoms in the thermoelectric conversion layer 11. The description of the first metal layer 12a also applies to the second metal layer 12b as long as there is no technical contradiction.

[0050] In the first metal layer 12a and the second metal layer 12b, the shapes of the first regions 12j may be the same or different. For example, the first regions 12j may exist in a layered form or in a fragmented form. Figure 1A As shown, for example, the first region 12j exists in a layer in the first metal layer 12a, and a plurality of first regions 12j separated from each other in a fragment shape exist in the second metal layer 12b.

[0051] Figure 1B FIG. 1 is a cross-sectional view schematically showing another example of the thermoelectric conversion element 10a. Figure 1B As shown, the first region 12j may exist in a layered form in the first metal layer 12a and the second metal layer 12b.

[0052] Figure 1C FIG. 1 is a cross-sectional view schematically showing another example of a thermoelectric conversion element. Figure 1C As shown, a plurality of segment-shaped first regions 12j separated from each other may exist in the first metal layer 12a and the second metal layer 12b.

[0053] Figure 1D , Figure 1E and Figure 1F 1 and 12 are cross-sectional views schematically showing another example of a thermoelectric conversion element. In the first metal layer 12a and the second metal layer 12b, only the first metal layer 12a may include the first region 12j. In this case, for example, Figure 1D As shown, a plurality of first regions 12j in the form of fragments separated from each other may exist in the first metal layer 12a. Figure 1E As shown, the first region 12j may exist in a layered form in the first metal layer 12a. Figure 1F As shown, a layer-shaped first region 12j and a segment-shaped first region 12j may exist separately in the first metal layer 12a.

[0054] The first region 12j further contains Mg, for example. In this case, the interface resistivity at the interface between the first metal layer 12a and the outside of the first metal layer 12a is likely to be lowered, and the resistance of the thermoelectric conversion element 10a is likely to be lowered.

[0055] like Figure 1AAs shown, the first metal layer 12 further includes, for example, a first electrode layer 12p and a first intermediate layer 12q. The first electrode layer 12p contains Cu. The first intermediate layer 12q is disposed between the first electrode layer 12p and the thermoelectric conversion layer 11 in the thickness direction of the first metal layer 12, and contains Mg and Cu. The first region 12j exists between the first intermediate layer 12q and the first electrode layer 12p in the thickness direction of the first metal layer 12. With such a configuration, 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.

[0056] As Figure 1A shown, the first metal layer 12a further includes, for example, a second intermediate layer 12r. The second intermediate layer 12r is disposed between the first electrode layer 12p and the first intermediate layer 12q in the thickness direction of the first metal layer 12a, and contains Mg and Cu. The first region 12j exists between the first intermediate layer 12q and the second intermediate layer 12r in the thickness direction of the first metal layer 12a. With such a configuration, 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.

[0057] The presence of the first intermediate layer 12q and the second intermediate layer 12r in the first metal layer 12a can be confirmed, for example, by observing a cross section of the first metal layer 12a using a transmission electron microscope (TEM) or an analytical electron microscope (AEM).

[0058] The first intermediate layer 12q and the second intermediate layer 12r are formed, for example, as diffusion layers. The first intermediate layer 12q and the second intermediate layer 12r are formed, for example, by diffusion of Mg from the raw material of the thermoelectric conversion layer 11 in the first metal layer 12a.

[0059] The change in the concentration of oxygen atoms on an atomic number basis in the thickness direction of the first metal layer 12a is not limited to a specific manner. For example, the concentration change satisfies the condition of 0.5% ≤ α at a position corresponding to the first region 12j. This concentration change is obtained by performing line composition analysis on a cross section of the first metal layer 12a in the thickness direction of the first metal layer 12a according to Auger electron spectroscopy. α is the maximum value of the oxygen atom concentration in this concentration change. With such a configuration, 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.

[0060] The above-mentioned concentration change may also satisfy the condition of 1% ≤ α, may also satisfy the condition of 2% ≤ α, may also satisfy the condition of 5% ≤ α, and may also satisfy the condition of 10% ≤ α.

[0061] The above concentration change satisfies the condition of α ≤ 50%, for example. In this case, the interface resistivity at the interface between the first metal layer 12a and the outside of the first metal layer 12a tends to become lower, and the resistance of the thermoelectric conversion element 10a tends to become lower.

[0062] The above concentration change may also satisfy the condition of α ≤ 45%, may also satisfy the condition of α ≤ 40%, and may also satisfy the condition of α ≤ 35%. The above concentration change may also satisfy, for example, α L ≤ α ≤ α H condition. In this condition, α L is one selected from 0.5%, 1%, 2%, 5% and 10%. α H is one selected from 35%, 40%, 45% and 50%.

[0063] The state of the interface between the first metal layer 12a and the outside of the first metal layer 12a can be evaluated by AES and TEM, for example. For example, the thermoelectric conversion element 10a is introduced into the inside of the AES apparatus, and the side surface of the thermoelectric conversion element 10a is reversely sputtered using an Ar ion gun equipped in the apparatus. Thereby, a clean surface as the object surface of AES is formed. From the viewpoints of the reverse sputtering rate and surface damage defined by the acceleration voltage and irradiation area of the Ar ion gun, the conditions for reverse sputtering are set to desired conditions. As an example, the acceleration voltage is 1 kV, and the processing area is 500 μm 2 . The reverse sputtering can be performed until the carbon atoms (C) and oxygen atoms (O) on the surface almost disappear. For example, a clean surface with almost no C and O on the surface of the thermoelectric conversion element 10a can be obtained by reverse sputtering for about 1 minute.

[0064] By performing line composition analysis on the clean surface thus obtained, the line profile of the sample cross section is obtained. In the line composition analysis, at least Mg, Cu, and O are taken as analysis objects. Other elements can also be analyzed simultaneously. The conditions for the line composition analysis can be appropriately set for each element. As an example, the line composition analysis can be performed under the conditions of an acceleration voltage of 10 kV, a probe current of 10 nA, and a magnification of 20,000 times.

[0065] The state of the interface can also be evaluated using TEM. The preparation for TEM observation is performed as follows, for example. First, Pt is vapor-deposited on the part to be observed by a prescribed method to form a protective film. An example of the vapor-deposition method is ion beam assisted deposition. Then, the part to be observed is processed by a prescribed method to produce a sample having a shape suitable for the measuring apparatus. An example of the processing method is the focused ion beam method. For the sample thus prepared, elemental analysis can be performed by using TEM and energy dispersive X-ray spectroscopy (EDX).

[0066] 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 only needs to be a shape capable of forming the thermoelectric conversion layer 11 containing the thermoelectric conversion material, and can be, for example, rectangular parallelepiped-shaped, cubic-shaped, substantially cubic-shaped, other prismatic-shaped, substantially prismatic-shaped, cylindrical or tubular.

[0067] The thickness of the thermoelectric conversion layer 11 is not limited to a specific value. Its thickness is, for example, 0.1 mm or more and 5.0 mm or less.

[0068] 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 is likely to exhibit the desired thermoelectric conversion characteristics. The thermoelectric conversion material is, for example, an N-type thermoelectric conversion material.

[0069] The thermoelectric conversion material contained in the thermoelectric conversion layer 11 has, for example, a crystal structure of the La2O3 type. In this case, the thermoelectric conversion element 10a is more likely to exhibit the desired thermoelectric conversion characteristics. Whether the thermoelectric conversion material has a crystal structure of the La2O3 type can be determined, for example, based on the X-ray diffraction measurement results of a sample of the thermoelectric conversion material. Figure 2 is a diagram schematically showing the crystal structure of the La2O3 type. In the case where the thermoelectric conversion material has a crystal structure of the La2O3 type, 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.

[0070] The thermoelectric conversion material further contains Te, for example. In this case, the thermoelectric conversion element 10a is more likely to exhibit the desired thermoelectric conversion characteristics.

[0071] The thermoelectric conversion material has, for example, a composition represented by Mg 3+m R a T b Sb 2-e-c Bi c Z eThe composition represented. 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.

[0072] As shown in FIG. 1, the first metal layer 12a and the second metal layer 12b each form, for example, an end face of the thermoelectric conversion element 10a in the thickness direction of the first metal layer 12a. The thickness of each of the first metal layer 12a and the second metal layer 12b is not limited to a specific value. For example, the thickness is 0.5 μm or more and 100 μm or less, preferably 0.5 μm or more and 10 μm or less. The thickness of the first metal layer 12a and the thickness of the second metal layer 12b may be the same or different. The first metal layer 12a and the second metal layer 12b are, for example, Cu or an alloy containing Cu. Each of the first metal layer 12a and the second metal layer 12b may also have a diffusion layer, which is a portion generated by the diffusion of a metal from the raw material of the thermoelectric conversion layer 11. Such a diffusion layer may be formed only in one of the first metal layer 12a and the second metal layer 12b, or may be formed in both the first metal layer 12a and the second metal layer 12b. When diffusion layers are present in both the first metal layer 12a and the second metal layer 12b, the thickness and composition of the diffusion layers in the first metal layer 12a and the second metal layer 12b may be the same or different. 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 material of the thermoelectric conversion layer 11 diffuses in the first metal layer 12a or the second metal layer 12b and alloyizes with Cu. Thus, the first metal layer 12a or the second metal layer 12b may contain such an alloy.

[0073] The thermoelectric conversion element 10a may also include another layer such as an electrode layer on a 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 electrodes. The other layer may be a single layer or multiple layers. 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.

[0074] The thermoelectric conversion element 10a can be manufactured, for example, by subjecting a laminate including a precursor of the thermoelectric conversion layer 11 and a precursor of a metal layer formed in contact with the precursor of the thermoelectric conversion layer 11 to a specific treatment including heating the laminate. As a result, 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.

[0075] Figure 3 is a flowchart showing a method for manufacturing the thermoelectric conversion element according to Embodiment 1. As Figure 3 shown, in step S11, a thermoelectric conversion material is produced. An example of a 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.

[0076] A solid-phase reaction is caused to occur in a state where Mg particles and at least one kind of particles selected from Sb particles and Bi particles, which are raw materials, are mixed, to obtain a powdery alloy containing Mg and at least one of Sb and Bi. The raw materials may also 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 a method for causing a solid-phase reaction is mechanical alloying. The alloy may also be obtained by methods other than solid-phase reaction, such as melting methods.

[0077] 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 spark plasma sintering or hot pressing. 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 may also be used as the thermoelectric conversion material.

[0078] Next, in step S12, a precursor of the metal layer is formed in contact with an end face of a precursor of the thermoelectric conversion layer including the thermoelectric conversion material. The method for forming the precursor of the metal layer is not limited to a specific method. Examples of the method for 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.

[0079] Next, in step S13, a specific treatment is performed on the precursor of the metal layer. The specific treatment includes heating a laminate of the precursor of the thermoelectric conversion layer 11 and the precursor of the metal layer. Thereby, a first region 12j is formed inside the first metal layer 12a. The specific treatment can also be, for example, a treatment including energizing by heating the laminate based on conditions assumed for the use of the thermoelectric conversion element 10a. 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 is performed. The specific treatment can also 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 is performed.

[0080] 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 specified value. ΔY is the amount of change in a specified characteristic of the element during the period from time t to time t + Δt. Y(t) is the value of the specified characteristic of the element at time t. The specified characteristic of the element is, for example, the resistance of the element.

[0081] (Embodiment 2)

[0082] Figure 4 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 can be directly connected to the electrode 31, or another layer can be disposed between the electrode 31 and the first metal layer 12a.

[0083] As Figure 4As 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 is in contact with the second surface 21a of the thermoelectric conversion layer 21. The second surface 21a is an end surface of the thermoelectric conversion layer 21 in the thickness direction of the electrode layer 22. The pair of electrode layers 22 are in contact with both end surfaces of the thermoelectric conversion layer 21 in the thickness direction of the electrode layer 22. The electrode layer 22 can be directly connected to the electrode 31, or another layer can be disposed between the electrode 31 and the electrode layer 22. The connection method of the P-type thermoelectric element 20a to the external electrode can be the same as or different from the connection method of the N-type thermoelectric conversion element 10a to the external electrode.

[0084] 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 can 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.

[0085] 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 coating layer, a Ni sputtering layer, or a Mo spray coating layer. When the P-type thermoelectric conversion material is bismuth telluride and is represented by the composition of Bi2Te x , in this case, x in the composition satisfies the condition of 2 < x < 4, for example. The composition of bismuth telluride can be Bi2Te3. It can also contain at least one selected from antimony and selenium in bismuth telluride. Bismuth telluride containing antimony has, for example, a composition of (Bi 1-y Sb y )2Te x . When the composition of the P-type thermoelectric conversion material has a composition of (Bi 1-y Sb y )2Te x , for example, it satisfies the condition of 0 < y < 1, and preferably satisfies the condition of 0.6 < y < 0.9.

[0086] Figure 5 is a cross-sectional view showing another example of the thermoelectric conversion module. As Figure 5As 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 denoted by the same reference numerals, and detailed descriptions thereof are omitted. The description of the thermoelectric conversion element 10a is also applicable to the thermoelectric conversion element 10b as long as there is no technical contradiction.

[0087] 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.

[0088] Figure 6 is a cross-sectional view showing another example of the thermoelectric conversion module. Figure 6 As shown, the thermoelectric conversion module 300 is configured in the same manner as the thermoelectric conversion module 100, except for the parts specifically described. As Figure 6 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 100.

[0089] (Embodiment 3)

[0090] Figure 7 is a side view showing the thermoelectric conversion system of Embodiment 3. As Figure 7As 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 portions of the P-type thermoelectric conversion element 20a and the N-type thermoelectric conversion element 10a.

[0091] The thermoelectric conversion system 500 further includes, for example, 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 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.

[0092] According to the thermoelectric conversion system 500, a power generation method can be provided, which includes generating an electric current by generating a temperature difference using heat from the heat source 70 in the thermoelectric conversion module 400.

[0093] The thermoelectric conversion elements in the above-described embodiments can be used 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.

[0094] (Supplementary Note)

[0095] Based on the above description, the following technology is disclosed.

[0096] (Technology 1)

[0097] A thermoelectric conversion element,

[0098] comprising a first metal layer, a second metal layer, and a thermoelectric conversion layer, the thermoelectric conversion layer being disposed between the first metal layer and the second metal layer in the thickness direction of the first metal layer and containing a thermoelectric conversion material, the thermoelectric conversion material containing Mg,

[0099] the first metal layer includes a first region disposed inside the first metal layer and containing oxygen atoms, and a second region other than the first region,

[0100] the content rate of oxygen atoms in the atomic number basis in the first region is higher than the content rate of oxygen atoms in the atomic number basis in the second region of the first metal layer, and higher than the content rate of oxygen atoms in the atomic number basis in the thermoelectric conversion layer.

[0101] (Technology 2)

[0102] The thermoelectric conversion element according to Technology 1, wherein the thermoelectric conversion material further contains at least one selected from Sb and Bi.

[0103] (Technology 3)

[0104] The thermoelectric conversion element according to Technology 1 or 2, wherein the first region further contains Mg.

[0105] (Technology 4)

[0106] The thermoelectric conversion element according to any one of Technologies 1 to 3,

[0107] The first metal layer further includes a first electrode layer and a first intermediate layer. The first electrode layer contains Cu, and the first intermediate layer is disposed between the first electrode layer and the thermoelectric conversion layer in the thickness direction of the first metal layer and contains Mg and Cu.

[0108] The first region exists between the first intermediate layer and the first electrode layer in the thickness direction of the first metal layer.

[0109] (Technology 5)

[0110] The thermoelectric conversion element according to any one of Technologies 1 to 3,

[0111] The first metal layer further includes a second intermediate layer. The second intermediate layer is disposed between the first electrode layer and the first intermediate layer in the thickness direction of the first metal layer and contains Mg and Cu.

[0112] The first region exists between the first intermediate layer and the second intermediate layer in the thickness direction of the first metal layer.

[0113] (Technology 6)

[0114] The thermoelectric conversion element according to any one of Technologies 1 to 5,

[0115] The change in the concentration of oxygen atoms in the thickness direction of the first metal layer satisfies a first condition expressed as 0.5% ≤ α at the position corresponding to the first region.

[0116] The change in concentration is obtained by performing line composition analysis on the cross-section of the first metal layer in the thickness direction of the first metal layer according to Auger electron spectroscopy.

[0117] In the first condition, α is the maximum value of the oxygen atom concentration in the change in concentration.

[0118] (Technology 7)

[0119] The thermoelectric conversion element according to Technique 6, wherein the concentration change satisfies a second condition of α ≤ 50%.

[0120] (Technique 8)

[0121] The thermoelectric conversion element according to any one of Techniques 1 to 7, wherein the thermoelectric conversion material has a crystal structure of the La2O3 type.

[0122] (Technique 9)

[0123] The thermoelectric conversion element according to any one of Techniques 1 to 8, wherein the thermoelectric conversion material further contains Te.

[0124] (Technique 10)

[0125] The thermoelectric conversion element according to any one of Techniques 1 to 9,

[0126] the thermoelectric conversion material has a composition represented by Mg 3+m R a T b Sb 2-e-c Bi c Z e ,

[0127] in the composition,

[0128] the element R is at least one element selected from Ca, Sr, Ba, and Yb,

[0129] the element T is at least one element selected from Mn and Zn,

[0130] the element Z is at least one element selected from Te, Se, Sc, Y, and La,

[0131] the value of m satisfies -0.39 ≤ m ≤ 0.42,

[0132] the value of a satisfies 0 ≤ a ≤ 0.12,

[0133] the value of b satisfies 0 ≤ b ≤ 0.48,

[0134] the value of c satisfies 0 ≤ c ≤ 1.6,

[0135] the value of e satisfies 0.001 ≤ e ≤ 0.06.

[0136] (Technique 11)

[0137] A thermoelectric conversion module includes:

[0138] a P-type thermoelectric conversion element;

[0139] an N-type thermoelectric conversion element; and

[0140] An electrode that electrically connects one end of the P-type thermoelectric conversion element and one end of the N-type thermoelectric conversion element

[0141] The N-type thermoelectric conversion element is the thermoelectric conversion element described in any one of Technologies 1 to 10.

[0142] (Technology 12)

[0143] A thermoelectric conversion system includes the thermoelectric conversion module described in Technology 11 and a heat source disposed on the electrode side.

[0144] (Technology 13)

[0145] 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 11.

[0146] (Technology 14)

[0147] A method for manufacturing a thermoelectric conversion element includes: subjecting a laminate including a precursor of a thermoelectric conversion layer and a precursor of a metal layer formed in contact with the precursor of the thermoelectric conversion layer to a specific treatment including heating the laminate to obtain a thermoelectric conversion element.

[0148] In the thermoelectric conversion element,

[0149] The thermoelectric conversion layer includes a thermoelectric conversion material, and the thermoelectric conversion material contains Mg.

[0150] The metal layer includes a first region disposed inside the metal layer and containing oxygen atoms, and a second region other than the first region.

[0151] The content rate of oxygen atoms in the first region based on the atomic number is higher than the content rate of oxygen atoms in the second region of the metal layer based on the atomic number, and higher than the content rate of oxygen atoms in the thermoelectric conversion layer based on the atomic number.

[0152] Examples

[0153] 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.

[0154] (Example 1)

[0155] Weigh approximately 1.3 g of Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01Powder of an alloy composed thereof. The inside of the glove box was maintained in an argon atmosphere until the thermoelectric conversion material was obtained. Then, the weighed powder was filled into the sintering space of a carbon mold, and powder pressing was performed using a carbon punch. The inner diameter of the mold was 10 mm. Then, the mold was placed in the chamber of a spark plasma sintering apparatus. The chamber was maintained in an argon atmosphere. Then, while applying a pressure of 50 MPa to the filler in the mold, an electric current was applied to the mold by the sintering apparatus. By applying the electric current, after the temperature of the mold reached 840 °C as the sintering temperature, this temperature was maintained for 10 minutes. Then, the electric current flowing through the mold was reduced, and the heating of the mold was stopped. After confirming that the temperature of the mold had dropped to room temperature, the sintered body was taken out from the inside of the mold, and the thermoelectric conversion material of Example 1 was obtained. The surface of the taken-out sintered body, i.e., the thermoelectric conversion material, that had contacted the inner surface of the mold was polished and then cleaned with acetone. The thickness of the sintered body of Example 1 was about 3 mm.

[0156] The surface roughness of both end faces in the thickness direction of the sintered body was adjusted, and then, both end faces of the sintered body were electroplated with Cu to form a plating layer. A commercially available plating solution was used, and plating was performed under the conditions recommended for this plating solution. After the plating was completed, the sintered body was cleaned.

[0157] The sintered body having the plating layer formed thereon was processed into a rectangular parallelepiped shape using a wire saw. Thus, in a plane parallel to the plating layer, the sintered body had a square contour with a side length of about 3 mm. In addition, the distance between the plating layers was about 2.9 mm.

[0158] 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 a heater block heated to 100 °C was in contact with the other plating layer. In this way, 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 carried out until |ΔR / (R(t)Δt)| became 1% / 100 hours or less. ΔR is the change in 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 it, M1 represents the thermoelectric conversion layer and M2 represents the metal layer.

[0159] 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 the method of measuring the resistance of the thermoelectric conversion element. As Figure 9As shown, a pair of external electrodes 71 are mounted on the thermoelectric conversion element 10a. A galvanometer 84 is electrically connected to both of the pair of electrodes 71 through a wire 85. A voltmeter 81 is connected to one external electrode 71 through a wire 82, and a probe 83 is 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 toward the other external electrode 71 at intervals of 50 μm in the direction indicated by the arrow J, the resistance is measured by the four-terminal measurement method. In the measurement of the resistance, a source meter (model: 2400) manufactured by KEITHLEY was used. Figure 10 FIG. is an example showing the measurement result of the resistance of the thermoelectric conversion element of Example 1. Figure 10 In [the figure], “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 conversion 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 .

[0160] Next, reverse sputtering based on Ar ions was performed on the side surface of the thermoelectric conversion element of Example 1 to produce a sample having a clean surface with almost disappeared C and O. The time required for reverse sputtering until a clean surface was obtained was about 1 minute. While maintaining such a clean surface state, the sample was moved into a scanning Auger electron spectroscopy apparatus PHI4800 manufactured by ULVAC-PHI, Inc., and line composition analysis was performed near the interface between the thermoelectric conversion layer and the metal layer (first metal layer). Thereby, the concentration profile of each atom on an atomic number basis was obtained. The results are shown in Figure 11 . In Figure 11 , M1 represents the range of the distance corresponding to the thermoelectric conversion layer, and M2 represents the range of the distance corresponding to the metal layer (first metal layer). According to Figure 11It is known that a thermoelectric conversion layer containing Mg, Sb, and Bi is joined to a metal layer containing Cu, and a concentration peak of O is visible inside the metal layer containing Cu, indicating the presence of an oxygen-containing site. As an example, the full width at half maximum of the peak of the oxygen atom concentration in the line composition analysis by AES is 0.3 μm, and it ranges from 0.05 μm to 3.0 μm depending on the site where the line composition analysis is performed. In addition, as an example, the maximum value of the oxygen atom concentration in the line composition analysis by AES is 10%, and it ranges from 0.5% to 35% depending on the site where the line composition analysis is performed. In the N2 region corresponding to the surface layer portion of the metal layer (the first metal layer), Cu exists at a high concentration.

[0161] Next, the tissue near the observation site of AES was processed into a specified shape using the focused ion beam method to obtain a specimen suitable for scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy (EDX). Using the obtained specimen, elemental analysis was performed using scanning transmission electron microscopy and EDX. As the scanning transmission electron microscope, the atomic resolution analytical electron microscope JEM-ARM200F manufactured by JEOL Ltd. was used, and the energy-dispersive X-ray analysis system NORAN System7 312E manufactured by Thermo Fisher Scientific Inc. was used for EDX. Figure 12 It is a photograph of the cross-section of the thermoelectric conversion element of Example 1 obtained by scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy. Figure 13A It shows Figure 12 a diagram showing the distribution of oxygen atoms in the field of view of the photograph shown. Figure 13B It shows Figure 12 a diagram showing the distribution of copper atoms in the field of view of the photograph shown. In Figure 12 , layered sites containing Mg and Cu were confirmed in the regions shown as N1 and N3. The concentration of Mg is relatively high in the N1 region, and the concentration of Cu is relatively high in the N3 region. It is considered that through specific treatment, Cu from the plating layer and Mg from the sintered body diffused to obtain such a thermoelectric conversion element.

[0162] 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. From the evaluation results of the interface between the thermoelectric conversion layer and the metal layer, it is known that there is an oxygen-containing site inside the metal layer (the first metal layer).

[0163] (Comparative Example 1)

[0164] Except for not performing specific treatment, the same procedures as in Example 1 were carried out to obtain the thermoelectric conversion element of Comparative Example 1.

[0165] 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. From the evaluation results of the interface between the thermoelectric conversion layer and the metal layer, it can be seen that at the interface between the thermoelectric conversion layer and the metal layer, the thermoelectric conversion layer is in direct contact with the oxygen-containing part.

[0166] (Comparative Example 2)

[0167] As the alloy powder, an alloy powder having a composition of Mg 3.2 Sb 1.0 Bi 0.99 Te 0.01 was used, and except for this, the same procedures as in Comparative Example 1 were carried out to obtain the 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. It can be seen that, similarly to Comparative Example 1, in Comparative Example 2, at the interface between the thermoelectric conversion layer and the metal layer, the thermoelectric conversion layer is in direct contact with the oxygen-containing part.

[0168] As shown in Table 1, the interfacial resistivity at the interface between the thermoelectric conversion layer and the metal layer in the thermoelectric conversion element of each example is lower than that in the thermoelectric conversion element of Comparative Examples 1 and 2. The following is revealed: By having a region containing oxygen atoms 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.

[0169] Table 1

[0170]

[0171] The thermoelectric conversion element of the present disclosure can be used in various applications including those of conventional thermoelectric conversion elements.

[0172] Description of Reference Numerals

[0173] 10a, 10b Thermoelectric conversion element

[0174] 11 Thermoelectric conversion layer

[0175] 12a First metal layer

[0176] 12b Second metal layer

[0177] 12j First region

[0178] 12p First electrode layer

[0179] 12q First intermediate layer

[0180] 12r Second intermediate layer

[0181] 20a P-type thermoelectric conversion element

[0182] 31 Electrode

[0183] 70 Heat source

[0184] 100, 200, 300, 400 Thermoelectric conversion module

[0185] 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 being disposed between the first metal layer and the second metal layer in the thickness direction of the first metal layer and containing a thermoelectric conversion material, the thermoelectric conversion material containing Mg, the first metal layer including a first region disposed inside the first metal layer and containing oxygen atoms, and a second region other than the first region, the content rate of oxygen atoms in the first region based on the number of atoms is higher than the content rate of oxygen atoms in the second region of the first metal layer based on the number of atoms, and higher than the content rate of oxygen atoms in the thermoelectric conversion layer based on the number of atoms.

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 region further contains Mg.

4. The thermoelectric conversion element according to claim 1, the first metal layer further includes a first electrode layer and a first intermediate layer, the first electrode layer containing Cu, the first intermediate layer being disposed between the first electrode layer and the thermoelectric conversion layer in the thickness direction of the first metal layer and containing Mg and Cu, the first region exists between the first intermediate layer and the first electrode layer in the thickness direction of the first metal layer.

5. The thermoelectric conversion element according to claim 4, the first metal layer further includes a second intermediate layer, the second intermediate layer being disposed between the first electrode layer and the first intermediate layer in the thickness direction of the first metal layer and containing Mg and Cu, the first region exists between the first intermediate layer and the second intermediate layer in the thickness direction of the first metal layer.

6. The thermoelectric conversion element according to claim 1, the change in the concentration of oxygen atoms in the thickness direction of the first metal layer satisfies a first condition represented by 0.5% ≤ α at a position corresponding to the first region, the change in concentration is obtained by performing line composition analysis on the cross section of the first metal layer in the thickness direction of the first metal layer according to Auger electron spectroscopy, in the first condition, α is the maximum value of the oxygen atom concentration in the change in concentration.

7. The thermoelectric conversion element according to claim 6, wherein the change in concentration satisfies a second condition of α ≤ 50%.

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

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

10. 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.

11. 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 according to claim 1.

12. A thermoelectric conversion system comprising the thermoelectric conversion module according to claim 11 and a heat source disposed on the electrode side.

13. A power generation method comprising: generating an electric current by utilizing heat from a heat source to create a temperature difference in the thermoelectric conversion module according to claim 11.

14. A method for manufacturing a thermoelectric conversion element comprising: subjecting a laminate including a precursor of a thermoelectric conversion layer and a precursor of a metal layer formed in contact with the precursor of the thermoelectric conversion layer to a specific treatment including heating the laminate to obtain a thermoelectric conversion element, In the thermoelectric conversion element, The thermoelectric conversion layer includes a thermoelectric conversion material that contains Mg, The metal layer includes a first region disposed inside the metal layer and containing oxygen atoms, and a second region other than the first region, The content rate of oxygen atoms in the first region based on the atomic number is higher than the content rate of oxygen atoms in the second region of the metal layer based on the atomic number, and higher than the content rate of oxygen atoms in the thermoelectric conversion layer based on the atomic number.

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