Method for manufacturing thermoelectric conversion element

Abstract

Provided is a novel technique capable of more reliably reducing resistance in a thermoelectric conversion element using a MgSbBiTe-based thermoelectric conversion material. This thermoelectric conversion element is provided with a first electrode, a second electrode, a first intermediate layer, a second intermediate layer, and a thermoelectric conversion layer. The first intermediate layer is provided between the thermoelectric conversion layer and the first electrode, the first intermediate layer is in contact with the thermoelectric conversion layer, the first electrode is in contact with the first intermediate layer, the second intermediate layer is provided between the thermoelectric conversion layer and the second electrode, the second intermediate layer is in contact with the thermoelectric conversion layer, the second electrode is in contact with the second intermediate layer, and the first electrode and the second electrode are configured from a CuZn alloy. The thermoelectric conversion layer is made of a MgSbBiTe-based thermoelectric conversion material, the composition of the first intermediate layer differs from the composition of the first electrode and the composition of the thermoelectric conversion layer, and the composition of the second intermediate layer differs from the composition of the second electrode and the composition of the thermoelectric conversion layer.

Description

[0001] This application is a divisional application of a Chinese patent application with an application date of November 12, 2018, an application number of 201880004572.3, and an invention title of "Thermoelectric Conversion Element and Thermoelectric Conversion Module". Technical Field

[0002] The present disclosure relates to a thermoelectric conversion element and a thermoelectric conversion module. Background Art

[0003] A thermoelectric conversion element composed of a thermoelectric conversion material and a pair of electrodes joined to the thermoelectric conversion material is known. An n-type thermoelectric conversion element can be constructed using an n-type thermoelectric conversion material. A p-type thermoelectric conversion element can be constructed using a p-type thermoelectric conversion material. A thermoelectric conversion module formed by combining an n-type thermoelectric conversion element and a p-type thermoelectric conversion element can generate electricity based on a temperature difference generated by the inflow of thermal energy.

[0004] Non-Patent Document 1 discloses a thermoelectric conversion element composed of an MgAgSb-based thermoelectric conversion material and a pair of Ag electrodes joined to the material.

[0005] Patent Document 1 discloses an MgSbBiTe-based thermoelectric conversion material.

[0006] Prior Art Documents

[0007] Patent Document 1: Japanese Patent No. 6127281

[0008] Non-Patent Document 1: D. Kraemer et.al., “High thermoelectric conversion efficiency of MgAgSb-based material with hot-pressed contacts”, Energy Environ. Sci., 2015, 8, 1299-1308 Summary of the Invention

[0009] As the resistance between a pair of electrodes in a thermoelectric conversion element becomes lower, the thermoelectric conversion performance of a thermoelectric conversion module including the element is improved.

[0010] The present disclosure provides a new technology that can more effectively reduce the resistance for a thermoelectric conversion element using an MgSbBiTe-based thermoelectric conversion material.

[0011] The present disclosure provides the following thermoelectric conversion element.

[0012] A thermoelectric conversion element includes a first electrode, a second electrode, a first intermediate layer, a second intermediate layer, and a thermoelectric conversion layer.

[0013] The first intermediate layer is disposed between the thermoelectric conversion layer and the first electrode,

[0014] and the first intermediate layer is in contact with the thermoelectric conversion layer,

[0015] and the first electrode is in contact with the first intermediate layer.

[0016] The second intermediate layer is disposed between the thermoelectric conversion layer and the second electrode,

[0017] and the second intermediate layer is in contact with the thermoelectric conversion layer,

[0018] and the second electrode is in contact with the second intermediate layer.

[0019] The first electrode and the second electrode are made of a CuZn alloy.

[0020] The thermoelectric conversion layer is made of a thermoelectric conversion material containing Mg.

[0021] The thermoelectric conversion material contains at least one element selected from Sb and Bi.

[0022] The thermoelectric conversion material contains at least one element selected from Se and Te.

[0023] The thermoelectric conversion material has a crystal structure of the La 2 O 3 type.

[0024] The composition of the first intermediate layer is different from the composition of the first electrode and the composition of the thermoelectric conversion layer.

[0025] The composition of the second intermediate layer is different from the composition of the second electrode and the composition of the thermoelectric conversion layer.

[0026] According to the present disclosure, for a thermoelectric conversion element using a MgSbBiTe-based thermoelectric conversion material, the resistance can be more effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram showing an example of the thermoelectric conversion element of the present disclosure.

[0028] Figure 2 is a schematic diagram showing an example of the thermoelectric conversion module of the present disclosure.

[0029] Figure 3 is a diagram showing the X-ray diffraction pattern of the thermoelectric conversion material fabricated in Example 1.

[0030] Figure 4It is a figure showing an energy dispersive X-ray analysis (hereinafter referred to as "EDX") spectrum of the thermoelectric conversion material fabricated in Example 1.

[0031] Figure 5A It is an image obtained by observing a cross-section of the thermoelectric conversion element fabricated in Example 1 using a scanning electron microscope (hereinafter referred to as "SEM").

[0032] Figure 5B It is a figure showing Figure 5A the results of X-ray analysis of the cross-section shown by EDX.

[0033] Figure 6A It is an image obtained by observing a cross-section of the thermoelectric conversion element fabricated in Example 2 using SEM.

[0034] Figure 6B It is a figure showing Figure 6A the results of X-ray analysis of the cross-section shown by EDX.

[0035] Figure 7A It is an image obtained by observing a cross-section of the thermoelectric conversion element fabricated in Comparative Example 1 using SEM.

[0036] Figure 7B It is a figure showing Figure 7A the results of X-ray analysis of the cross-section shown by EDX.

[0037] Explanation of Reference Numerals

[0038] 1 (n-type) thermoelectric conversion element

[0039] 2 thermoelectric conversion layer

[0040] 3 intermediate layer

[0041] 3a first intermediate layer

[0042] 3b second intermediate layer

[0043] 4 electrode

[0044] 4a first electrode

[0045] 4b second electrode

[0046] 5a first surface

[0047] 5b second surface

[0048] 11 thermoelectric conversion module

[0049] 12a, 12b, 12c, 12d bonding material layer

[0050] 13a first external electrode

[0051] 13b Second external electrode

[0052] 13c Third external electrode

[0053] 21 p-type thermoelectric conversion element

[0054] 22 p-type thermoelectric conversion section

[0055] 23a Third electrode

[0056] 23b Fourth electrode

[0057] 24a Third surface

[0058] 24b Fourth surface

[0059] 51 Thermoelectric conversion layer

[0060] 52 Metamorphic layer

[0061] 53 Ni layer Detailed implementation mode

[0062] (Incorporated by reference)

[0063] In this application, Japanese Patent No. 6127281 publication and its corresponding US Published Patent No. 2017 / 0117453 are referred to and incorporated herein by reference.

[0064] (Insight underlying this disclosure)

[0065] According to the research of the present inventors, the bonding property between the MgSbBiTe-based thermoelectric conversion material and the electrode is greatly affected by Mg contained in the material. More specifically, in the MgSbBiTe-based thermoelectric conversion material, due to the high diffusibility of Mg contained in the material, the bonding property with the electrode is reduced. In the MgAgSb-based thermoelectric conversion material disclosed in Non-Patent Document 1, there is no report on the influence of Mg on the bonding property with the electrode. According to further research by the present inventors, the bonding property between the MgSbBiTe-based thermoelectric conversion material and the electrode is improved by the first electrode and the second electrode made of a CuZn alloy, and the first intermediate layer and the second intermediate layer. By improving this bonding property, for a thermoelectric conversion element using the MgSbBiTe-based thermoelectric conversion material, the resistance can be more effectively reduced.

[0066] (Embodiments of this disclosure)

[0067] Hereinafter, embodiments of this disclosure will be described with reference to the drawings.

[0068] [Thermoelectric conversion element]

[0069] An example of the thermoelectric conversion element of the present disclosure is shown in Figure 1 . Figure 1 The thermoelectric conversion element 1 of Figure 1 includes a thermoelectric conversion layer 2, a first intermediate layer 3a, a second intermediate layer 3b, a first electrode 4a, and a second electrode 4b. The thermoelectric conversion layer 2 has a first surface 5a and a second surface 5b. The second surface 5b is the surface on the side opposite to the first surface 5a. The first intermediate layer 3a is provided between the thermoelectric conversion layer 2 and the first electrode 4a. The first intermediate layer 3a is in contact with the thermoelectric conversion layer 2. The first electrode 4a is in contact with the first intermediate layer 3a. The second intermediate layer 3b is provided between the thermoelectric conversion layer 2 and the second electrode 4b. The second intermediate layer 3b is in contact with the thermoelectric conversion layer 2. The second electrode 4b is in contact with the second intermediate layer 3b.

[0070] In Figure 1 the element 1 of Figure 1 , the shape of the thermoelectric conversion layer 2 is a rectangular parallelepiped. However, the shape of the thermoelectric conversion layer 2 is not limited to a rectangular parallelepiped. In Figure 1 the element 1 of Figure 1 , the first surface 5a and the second surface 5b of the thermoelectric conversion layer 2 are parallel to each other. However, as long as the first surface 5a does not contact the second surface 5b, they may not be parallel to each other.

[0071] The thermoelectric conversion layer 2 is made of a thermoelectric conversion material A containing Mg. The thermoelectric conversion material A contains at least one element selected from Sb, Bi, and Te. In addition, the thermoelectric conversion material A contains at least one element selected from Se and Te. The thermoelectric conversion material A has a La 2 O 3 -type crystal structure.

[0072] The thermoelectric conversion material A may have a composition represented by the formula (I): Mg 3+m A a B b D 2-e E e and is of the n-type. The element 1 having the thermoelectric conversion layer 2 made of the n-type thermoelectric conversion material A is an n-type thermoelectric conversion element.

[0073] A in the formula (I) is at least one element selected from Ca, Sr, Ba, and Yb. B is at least one element selected from Mn and Zn. D is at least one element selected from Sb and Bi. E is at least one element selected from Se and Te. The value of m in the formula (I) is in the range of -0.39 or more and 0.42 or less. The value of a is in the range of 0 or more and 0.12 or less. The value of b is in the range of 0 or more and 0.48 or less. The value of e is in the range of 0.001 or more and 0.06 or less.

[0074] The value of e in the formula (I) may be in the range of 0.004 or more and 0.020 or less. In this case, the thermoelectric conversion performance of the element 1 and the thermoelectric conversion module having the element 1 can be improved.

[0075] In formula (I), m, a, and b can satisfy formula (II): m = m' - a - b. The value of m' in formula (II) is in the range of 0 or more and 0.21 or less. At least one of the values selected from the value of a and the value of b in formula (II) can be greater than 0 (zero). In this case, the thermoelectric conversion performance of element 1 and the thermoelectric conversion module including element 1 can be improved.

[0076] The values of a and b in formula (I) can be 0 (zero). In this case, the thermoelectric conversion performance of element 1 and the thermoelectric conversion module including element 1 can be improved.

[0077] In formula (I), D can be Sb and Bi, and E can be Te. In this case, the thermoelectric conversion performance of element 1 and the thermoelectric conversion module including element 1 can be improved.

[0078] The thermoelectric conversion material A can have any composition described in Japanese Patent No. 6127281 or the corresponding US Published Patent No. 2017 / 0117453 and within the range of formula (I).

[0079] The first electrode 4a is made of a CuZn alloy. The second electrode 4b is made of a CuZn alloy. The composition of the first electrode 4a and the composition of the second electrode 4b can be the same or different. The composition of the CuZn alloy is represented by weight ratio, for example, in the range of Cu:Zn = 99:1 to 57:43, or can also be in the range of 68:32 to 63:37. The CuZn alloy can contain other metal elements in a range of 11 wt% or less in addition to Cu and Zn. The CuZn alloy can be an alloy classified as brass. Furthermore, like other ordinary alloys, impurities are allowed to exist in the CuZn alloy.

[0080] The first electrode 4a is joined to the first surface 5a so as to cover at least a part of the first surface 5a. The first electrode 4a can also be joined to the first surface 5a so as to cover the entire first surface 5a. The second electrode 4b is joined to the second surface 5b so as to cover at least a part of the second surface 5b. The second electrode 4b can also be joined to the second surface 5b so as to cover the entire second surface 5b.

[0081] There is no limitation on the thickness and shape of the first electrode 4a and the second electrode 4b.

[0082] The composition of the first intermediate layer 3a is different from both the composition of the first electrode 4a and the composition of the thermoelectric conversion layer 2 (i.e., the composition of the thermoelectric conversion material A). The composition of the second intermediate layer 3b is different from both the composition of the second electrode 4b and the composition of the thermoelectric conversion layer 2. The composition of the first intermediate layer 3a and the composition of the second intermediate layer 3b can be the same or different.

[0083] The first intermediate layer 3a and the second intermediate layer 3b contain, for example, Cu, Zn, and Mg. In this case, the content rate of Cu is, for example, 50% by weight or more and 70% by weight or less. The content rate of Zn is, for example, 25% by weight or more and 35% by weight or less. The content rate of Mg is, for example, 0.1% by weight or more and 25% by weight or less. When the first intermediate layer 3a and the second intermediate layer 3b contain Cu, Zn, and Mg, the content rate of Mg can be smaller than the content rate of at least one element selected from Cu and Zn. The first intermediate layer 3a and the second intermediate layer 3b sometimes further contain elements (excluding Mg) that constitute the thermoelectric conversion material A. In this case, the content rates of these elements in the first intermediate layer 3a and the second intermediate layer 3b are generally smaller than the content rate of Mg. The first intermediate layer 3a and the second intermediate layer 3b may not contain elements (excluding Mg) that constitute the thermoelectric conversion material A.

[0084] The first intermediate layer 3a is disposed between the first surface 5a and the first electrode 4a so as to cover at least a part of the first surface 5a. The first intermediate layer 3a may also be disposed between the first surface 5a and the first electrode 4a so as to cover the entire first surface 5a. The second intermediate layer 3b is disposed between the second surface 5b and the second electrode 4b so as to cover at least a part of the second surface 5b. The second intermediate layer 3b may also be disposed between the second surface 5b and the second electrode 4b so as to cover the entire second surface 5b.

[0085] The thicknesses of the first intermediate layer 3a and the second intermediate layer 3b are, for example, 0.1 μm or more and 300 μm or less, and may also be 3 μm or more and 30 μm or less. The thickness of the first intermediate layer 3a and the thickness of the second intermediate layer 3b may be the same or different.

[0086] The shapes of the first intermediate layer 3a and the second intermediate layer 3b are not limited.

[0087] The thermoelectric conversion element of the present disclosure may include at least one selected from other layers and members other than those described above.

[0088] The use of the thermoelectric conversion element of the present disclosure is not limited. The use is, for example, a thermoelectric conversion module.

[0089] (Manufacturing method)

[0090] An example of a manufacturing method of the thermoelectric conversion element of the present disclosure is shown below. However, the manufacturing method of the thermoelectric conversion element of the present disclosure is not limited to the following example.

[0091] First, a thermoelectric conversion layer 2 made of the thermoelectric conversion material A is produced. The production method of the thermoelectric conversion layer 2 is, for example, the method described in Japanese Patent No. 6127281 or the corresponding US Published Patent No. 2017 / 0117453.

[0092] Next, a CuZn alloy layer is formed on the first surface 5a and the second surface 5b of the produced thermoelectric conversion layer 2. The CuZn alloy layer can be formed, for example, by a spark plasma sintering method (hereinafter referred to as the "SPS method"). However, the method for forming the CuZn alloy layer is not limited to the SPS method. During the formation of the CuZn alloy layer, a first intermediate layer 3a, a second intermediate layer 3b, a first electrode 4a, and a second electrode 4b are formed. It is speculated that the diffusion of Mg from the thermoelectric conversion layer 2 is involved in the formation of these layers and components. Considering the diffusion of Mg, during the formation of the CuZn alloy layer by various methods including the SPS method, a temperature of about 400 to 800 degrees Celsius is used, for example.

[0093] [Thermoelectric conversion module]

[0094] An example of the thermoelectric conversion module of the present disclosure is shown in Figure 2 . Figure 2 The thermoelectric conversion module 11 shown in includes an n-type thermoelectric conversion element 1 and a p-type thermoelectric conversion element 21.

[0095] The n-type thermoelectric conversion element 1 includes a first electrode 4a, a second electrode 4b, a first intermediate layer 3a, a second intermediate layer 3b, and a thermoelectric conversion layer 2 as an n-type thermoelectric conversion section. The n-type thermoelectric conversion section has a first surface 5a and a second surface 5b. The second surface 5b is the surface on the opposite side of the first surface 5a. The first intermediate layer 3a is provided between the n-type thermoelectric conversion section and the first electrode 4a. The first intermediate layer 3a is in contact with the n-type thermoelectric conversion section. The first electrode 4a is in contact with the first intermediate layer 3a. The second intermediate layer 3b is provided between the n-type thermoelectric conversion section and the second electrode 4b. The second intermediate layer 3b is in contact with the n-type thermoelectric conversion section. The second electrode 4b is in contact with the second intermediate layer 3b.

[0096] The p-type thermoelectric conversion element 21 includes a third electrode 23a, a fourth electrode 23b, and a p-type thermoelectric conversion section 22. The p-type thermoelectric conversion section 22 has a third surface 24a and a fourth surface 24b. The fourth surface 24b is the surface on the opposite side of the third surface 24a. The p-type thermoelectric conversion section 22 is provided between the third electrode 23a and the fourth electrode 23b. The third electrode 23a and the fourth electrode 23b are in contact with the p-type thermoelectric conversion section 22.

[0097] One electrode of the n-type thermoelectric conversion element 1 and one electrode of the p-type thermoelectric conversion element 21 are electrically connected to each other. In Figure 2In the example, the first electrode 4a of the n-type thermoelectric conversion element 1 and the third electrode 23a of the p-type thermoelectric conversion element 21 are electrically connected to each other via the first external electrode 13a. A conductive bonding material layer 12a is disposed between the first electrode 4a and the first external electrode 13a. A conductive bonding material layer 12c is disposed between the third electrode 23a and the first external electrode 13a. In addition, the second electrode 4b, which is the other electrode of the n-type thermoelectric conversion element 1, is electrically connected to the second external electrode 13b via a conductive bonding material layer 12b. The fourth electrode 23b, which is the other electrode of the p-type thermoelectric conversion element 21, is electrically connected to the third external electrode 13c via a conductive bonding material layer 12d. In the thermoelectric conversion module 11, power can be taken out to the outside via the second external electrode 13b and the third external electrode 13c.

[0098] The p-type thermoelectric conversion element 21 can use a known element.

[0099] Regarding the constitution of the bonding material layers 12a, 12b, 12c, and 12d, there is no limitation as long as they have conductivity.

[0100] The first external electrode 13a, the second external electrode 13b, and the third external electrode 13c can use known external electrodes.

[0101] The thermoelectric conversion module 11 can be manufactured by a known method.

[0102] The use of the thermoelectric conversion module of the present disclosure is not limited. The thermoelectric conversion module of the present disclosure can be used for various uses including, for example, uses including conventional thermoelectric conversion modules.

[0103] Example

[0104] Hereinafter, the thermoelectric conversion element of the present disclosure will be described in more detail with reference to the examples. The thermoelectric conversion element of the present disclosure is not limited to the various modes shown in the following examples.

[0105] (Example 1)

[0106] (Production of sintered body)

[0107] A sintered body made of the thermoelectric conversion material A was manufactured as follows. The composition of the thermoelectric conversion material A is Mg 3.08 Sb 1.49 Bi 0.49 Te 0.02 .

[0108] First, granular antimony (5.48 g, 0.045 mol) and granular bismuth (3.01 g, 0.0144 mol) were melted at a temperature in the range of 1000 to 1500 degrees Celsius by an arc melting method. Thus, an alloy of antimony (Sb) and bismuth (Bi) was obtained. Then, the obtained alloy was pulverized in a mortar to form a powder of SbBi.

[0109] Next, magnesium powder (2.33 g, 0.096 mol) and tellurium powder (0.0474 g, 0.0006 mol) were added to the SbBi powder. Then, these powders were thoroughly mixed. The molar ratio of Mg, Sb, Bi, and Te as starting materials was Mg:Sb:Bi:Te = 0.096:0.045:0.0144:0.0006, that is, 3.20:1.50:0.48:0.02.

[0110] Next, the mixed powder was fed to a tablet press to form a tablet. Then, the tablet was placed in a carbon crucible. The carbon crucible was filled with argon. Then, the tablet was heated at a temperature in the range of 800 to 1000 degrees Celsius for 10 seconds. By heating, the tablet was melted to form an ingot.

[0111] Next, the ingot was placed in a mortar placed in a glove box filled with argon. The ingot was pulverized in the mortar to form a powder of MgSbBiTe. The particle size of the formed powder was 100 μm or less.

[0112] Then, the MgSbBiTe powder was sintered by the SPS method to form a sintered body. The sintering by the SPS method was carried out as follows. First, the MgSbBiTe powder was filled into a cylindrical graphite mold (i.e., a sintering mold). The mold had an outer shape of 50 mm and an inner diameter of 10 mm. The filling was carried out in a glove box filled with argon. Next, the mold was placed in the chamber of a spark plasma sintering apparatus. The chamber was controlled to be an argon atmosphere. Then, a pressure of 50 MPa was applied to the powder filled in the mold, and a pulsed current was applied to the mold by the sintering apparatus. By applying the current, a heating rate of 20 degrees Celsius per minute was achieved. After the temperature of the mold reached 600 degrees Celsius as the sintering temperature, this temperature was maintained for 30 minutes. Next, the heating of the mold was stopped by stopping the current. After the temperature of the mold decreased to room temperature, a cylindrical sintered body was taken out from the mold.

[0113] Through evaluation by X-ray diffraction measurement, it was confirmed that the thermoelectric conversion material A constituting the sintered body had a La 2 O 3 -type crystal structure. The X-ray diffraction pattern of the thermoelectric conversion material A obtained by X-ray diffraction measurement is shown in Figure 3 . Furthermore, CuKα rays were used for the X-ray diffraction measurement.

[0114] Through EDX-based evaluation, it was confirmed that the composition of the thermoelectric conversion material A constituting the sintered body was Mg 3.08 Sb 1.49 Bi 0.49 Te 0.02 . The EDX spectrum of the thermoelectric conversion material A is shown in Figure 4 . For EDX, an energy-dispersive X-ray spectrometer for SEM (manufactured by Bruker, XFlash6|10) was used. The SEM combined with the above spectrometer was a field emission type SEM (FE-SEM; manufactured by Hitachi High-Technologies Corporation, SU8220).

[0115] (Formation of CuZn alloy layer)

[0116] The upper and lower surfaces of the cylindrical sintered body were polished using #400 sandpaper. The polishing was carried out inside a glove box filled with argon. The height of the polished sintered body was 3.5 mm.

[0117] Next, a CuZn alloy layer was formed on the upper surface (the first surface) and the lower surface (the second surface) of the sintered body by the SPS method. The formation of the CuZn alloy layer by the SPS method was carried out as follows.

[0118] First, the polished sintered body was placed in a cylindrical mold used for the production of the sintered body. Next, with the mold standing upright, 0.336 g of CuZn powder was filled into the mold from above. The CuZn powder accumulated on the first surface of the sintered body housed in the mold. Then, the accumulated CuZn powder was gently pressed. Next, the mold was slowly turned over to swap the upper and lower surfaces of the mold. Then, with the mold standing upright, 0.336 g of CuZn powder was filled into the mold from the swapped upper surface. The CuZn powder accumulated on the second surface of the sintered body housed in the mold. Next, the accumulated CuZn powder was gently pressed. The composition of the alloy constituting the CuZn powder was Cu:Zn = 65:35 (weight ratio). Placing the sintered body in the mold and filling the mold with CuZn powder were carried out inside a glove box filled with argon.

[0119] Then, the mold is stored in the chamber of the spark plasma sintering apparatus. The chamber is controlled to an argon gas atmosphere. Next, a pressure of 90 MPa is applied to the sintered body and the CuZn powder filled in the mold, and a pulsed current is applied to the mold by the sintering apparatus. By applying the current, a heating rate of 60 degrees Celsius per minute is achieved. After the temperature of the mold reaches 600 degrees Celsius as the sintering temperature, this temperature is maintained for 15 minutes. Then, the heating of the mold is stopped by stopping the current. After the temperature of the mold has dropped to room temperature, a cylindrical sintered body having CuZn alloy layers on its upper and lower surfaces is taken out from the mold.

[0120] Next, the surface of the CuZn alloy layer of the taken-out sintered body is polished using #400 sandpaper. The polishing is carried out inside a glove box filled with argon. The height of the polished sintered body is 4.0 mm. Then, the polished sintered body is cut using a cutter to form a cuboid-shaped thermoelectric conversion element having dimensions of 3.5 mm in width, 3.5 mm in depth, and 4.0 mm in height.

[0121] The state of the portion near the interface between the sintered body and the CuZn alloy layer in the cut surface of the formed thermoelectric conversion element is evaluated by SEM. In addition, the composition of the portion near the interface between the sintered body and the CuZn alloy layer is evaluated by X-ray analysis of the above-mentioned cut surface using EDX. The image of the portion near the above-mentioned interface in the cut surface observed by SEM is shown in Figure 5A . The result of X-ray analysis of the above-mentioned portion using EDX is shown in Figure 5B . The X-ray analysis using EDX is carried out along the line segment OX of the observation image shown in Figure 5A . The change in composition based on the distance from the point O of the line segment OX is shown in Figure 5B . SEM and EDX used the above-mentioned apparatuses.

[0122] As shown in Figure 5A and Figure 5B , near the interface between the sintered body and the CuZn alloy layer, two boundaries M1 and M2 where the composition changes greatly are observed. The portion between the point O and the boundary M1 is composed of Cu and Zn, that is, it is the CuZn alloy layer that functions as the electrode 4. The portion between the boundary M2 and the point X is composed of Mg, Sb, Bi, and Te, that is, it is the thermoelectric conversion layer 2 that functions as the thermoelectric conversion portion. Furthermore, due to the small content rate, Figure 5B does not clearly show a figure corresponding to Te. On the other hand, the portion between the boundary M1 and the boundary M2 is a layer composed of Cu, Zn, and Mg and having a composition different from that of the electrode 4 and the sintered body 2. That is, between the electrode 4 and the thermoelectric conversion layer 2, the formation of an intermediate layer 3 containing Cu, Zn, and Mg is confirmed. As shown in Figure 5AAs shown, the electrode 4, the intermediate layer 3, and the thermoelectric conversion layer 2 are all dense layers.

[0123] Next, the resistance value between a pair of CuZn alloy layers in the formed thermoelectric conversion element was measured by the four-terminal method. The measurement was performed using a Keithley 2400 Source Meter manufactured by Toyo Iron Triangle Co., Ltd. The measured resistance value was 16.4 mΩ. In addition, the resistivity ρ calculated from the measured resistance value by the following formula was 50.2 μΩ·m.

[0124] ρ = R × A / L

[0125] In the above formula, R is the resistance value between the CuZn alloy layers, A is the cross-sectional area of the thermoelectric conversion element (3.5 mm × 3.5 mm), and L is the height of the thermoelectric conversion element (4.0 mm).

[0126] (Example 2)

[0127] The sintering temperature for forming the sintered body was changed to 500 degrees Celsius, and the sintering time was changed to 15 minutes. Otherwise, the thermoelectric conversion element was fabricated in the same manner as in Example 1. Through evaluation by X-ray diffraction measurement, it was confirmed that the thermoelectric conversion material A constituting the sintered body had a La 2 O 3 -type crystal structure. In addition, through evaluation by EDX, it was confirmed that the composition of the thermoelectric conversion material A constituting the sintered body was the same as that in Example 1, which was Mg 3.08 Sb 1.49 Bi 0.49 Te 0.02 .

[0128] Similar to Example 1, SEM was used to evaluate the state of the portion near the interface between the sintered body and the CuZn alloy layer in the cross-section of the formed thermoelectric conversion element. In addition, through X-ray analysis of the above cross-section using EDX, the composition of the portion near the interface between the sintered body and the CuZn alloy layer was evaluated. The image of the portion near the above interface in the cross-section observed by SEM is shown in Figure 6A . The result of X-ray analysis of the above portion using EDX is shown in Figure 6B . The X-ray analysis using EDX was performed along the line segment OX of the observed image shown in Figure 6A . Figure 6B shows the change in composition based on the distance from the point O of the line segment OX.

[0129] As Figure 6A and Figure 6BAs shown, near the interface between the sintered body and the CuZn alloy layer, two boundaries M1 and M2 with greatly changed compositions were observed. The portion between point O and boundary M1 is composed of Cu and Zn, that is, it is the CuZn alloy layer that functions as electrode 4. The portion between boundary M2 and point X is composed of Mg, Sb, Bi, and Te, that is, it is the thermoelectric conversion layer 2 that functions as the thermoelectric conversion section. Furthermore, due to the small content rate, Figure 6B does not clearly show the figure corresponding to Te. On the other hand, the portion between boundary M1 and boundary M2 is a layer composed of Cu, Zn, and Mg and having a composition different from that of electrode 4 and the sintered body 2. That is, between electrode 4 and the thermoelectric conversion layer 2, the formation of the intermediate layer 3 containing Cu, Zn, and Mg was confirmed. As Figure 6A shown, electrode 4, the intermediate layer 3, and the thermoelectric conversion layer 2 are all dense layers.

[0130] Next, in the same manner as in Example 1, the resistance value and resistivity ρ between a pair of CuZn alloy layers in the formed thermoelectric conversion element were evaluated. The measured resistance value was 7.05 mΩ. In addition, the obtained resistivity ρ was 21.6 μΩ·m.

[0131] (Comparative Example 1)

[0132] The upper and lower surfaces of the cylindrical sintered body fabricated in the same manner as in Example 1 were polished using #400 sandpaper. The polishing was carried out in the atmosphere. The height of the polished sintered body was 0.7 mm. Then, Ni layers were formed on the upper surface (the first surface) and the lower surface (the second surface) of the sintered body by electrolytic plating. The thickness of each formed Ni layer was approximately 5 μm. Next, the sintered body with the Ni layer was cut using a cutter to form a rectangular parallelepiped-shaped thermoelectric conversion element having dimensions of width 1.0 mm, depth 1.0 mm, and height 0.71 mm.

[0133] The state of the portion near the interface between the sintered body and the Ni layer in the cut surface of the formed thermoelectric conversion element was evaluated by SEM. In addition, the composition of the portion near the interface between the sintered body and the Ni layer was evaluated by X-ray analysis of the above cut surface using EDX. The image of the portion near the above interface in the cut surface observed by SEM is shown in Figure 7A . The result of X-ray analysis of the above portion using EDX is shown in Figure 7B . The X-ray analysis using EDX was carried out along the Figure 7A shown observation image line segment OX. Figure 7B shows the change in composition based on the distance from point O of the line segment OX.

[0134] As Figure 7A and Figure 7BAs shown, near the interface between the sintered body and the Ni layer, two boundaries M1 and M2 with greatly changed compositions were observed. The portion between point O and boundary M1 is composed of Ni, that is, the Ni layer that functions as electrode 53. The portion between boundary M2 and point X is composed of Mg, Sb, Bi, and Te, that is, the thermoelectric conversion layer 51 that functions as the thermoelectric conversion section. Furthermore, due to the small content rate, Figure 7B the figure corresponding to Te is not clearly shown in Figure 7B . On the other hand, the portion between boundary M1 and boundary M2 is a metamorphic layer 52 that is composed of Mg, Sb, Bi, and Te in the same way as the thermoelectric conversion layer 51, but has a composition completely different from that of the thermoelectric conversion layer 51. More specifically, in the metamorphic layer 52, the content rate of Mg decreases sharply compared with the thermoelectric conversion layer 51. In addition, as Figure 7A shown, a plurality of pores were observed in the metamorphic layer 52. Judging from the composition and the formation of the pores, it is speculated that the metamorphic layer 52 was formed due to the diffusion and outflow of Mg from the thermoelectric conversion layer 51 near the interface.

[0135] Next, in the same manner as in Example 1, the resistance value and resistivity ρ between a pair of Ni layers in the formed thermoelectric conversion element were measured. In the calculation of the resistivity ρ, R in the above formula is the resistance value between the Ni layers, A is the cross-sectional area (1.0 mm × 1.0 mm) of the thermoelectric conversion element, and L is the height (0.71 mm) of the thermoelectric conversion element. The measured resistance value was 841 mΩ. In addition, the obtained resistivity ρ was 1185 μΩ·m.

[0136] The resistance values and resistivity ρ between the electrodes in the thermoelectric conversion elements of Example 1, Example 2, and Comparative Example 1 are summarized in Table 1 below.

[0137] Table 1

[0138] Resistance value (mΩ) Resistivity (μΩ·m) Example 1 16.4 50.2 Example 2 7.05 21.6 Comparative Example 1 841 1185

[0139] As shown in Table 1, in the thermoelectric conversion elements of Example 1 and Example 2, the resistance was greatly reduced compared with the thermoelectric conversion element of Comparative Example 1.

[0140] Industrial Applicability

[0141] The thermoelectric conversion element of the present disclosure can be used for various applications including the applications of conventional thermoelectric conversion elements.

Claims

1. A manufacturing method of a thermoelectric conversion element, comprising: forming a first metal layer containing Cu on a first surface of the thermoelectric conversion layer; and forming a first electrode and a first intermediate layer from the first metal layer, wherein the thermoelectric conversion layer is composed of a thermoelectric conversion material containing Mg and at least one element selected from Sb and Bi, the first intermediate layer is disposed between the thermoelectric conversion layer and the first electrode, the first intermediate layer is in contact with the thermoelectric conversion layer, the first electrode is in contact with the first intermediate layer, and the Cu content rate in the first electrode is greater than the Cu content rate in the first intermediate layer.

2. The manufacturing method of the thermoelectric conversion element according to claim 1, The thermoelectric conversion material has a composition represented by the formula (I): Mg 3+m A a B b D 2-e E e and is of the n-type, in the formula (I), A is at least one element selected from Ca, Sr, Ba, and Yb, B is at least one element selected from Mn and Zn, D is at least one element selected from Sb and Bi, E is at least one element selected from Se and Te, the value of m ranges from -0.39 or more and 0.42 or less, the value of a ranges from 0 or more and 0.12 or less, the value of b ranges from 0 or more and 0.48 or less, and the value of e ranges from 0.001 or more and 0.06 or less.

3. The manufacturing method of the thermoelectric conversion element according to claim 1, the first electrode contains Cu, and the Cu content rate in the first electrode is 57 wt% or more and 99 wt% or less.

4. The manufacturing method of the thermoelectric conversion element according to claim 1, wherein the first intermediate layer further contains Zn.

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