Thermoelectric conversion material and thermoelectric conversion element using the same

Abstract

The thermoelectric conversion material disclosed herein is a polycrystalline body composed of a plurality of crystal grains, and the thermoelectric conversion material has a formula (I): Mg 3+ m Sb a Bi 2‑a‑c A c A in formula (I) is at least one element selected from Se and Te. The value of m is 0.01 or more and 0.5 or less. The value of a is 0 or more and 1.0 or less. The value of c is 0.001 or more and 0.6 or less. The thermoelectric conversion material disclosed in the present invention has a Mg-rich portion.

Description

Technical Field

[0001] The present disclosure relates to a thermoelectric conversion material and a thermoelectric conversion element using the same. Background Art

[0002] When a temperature difference occurs at both ends of a thermoelectric conversion material, an electromotive force proportional to the temperature difference is generated. This phenomenon of thermal energy being converted into electrical energy is known as the Seebeck effect. Thermoelectric power generation technology is a technology that directly converts thermal energy into electrical energy by utilizing the Seebeck effect. As is well known to those skilled in the art in the technical field of thermoelectric conversion materials, the performance of thermoelectric conversion materials used for thermoelectric conversion can be evaluated by the thermoelectric conversion performance index ZT. The thermoelectric conversion performance index ZT uses the Seebeck coefficient S, electrical conductivity σ and thermal conductivity κ of the material, and is given by the formula: ZT = S 2 The higher the thermoelectric conversion performance index ZT is, the higher the thermoelectric conversion efficiency of the thermoelectric conversion material is.

[0003] A thermoelectric conversion element using a thermoelectric conversion material is known. According to the thermoelectric conversion element, it is possible to generate electricity based on a temperature difference caused by an inflow of thermal energy.

[0004] Patent Documents 1 and 2 and Non-Patent Document 1 disclose a Mg 3 (Sb,Bi) 2 Department of thermoelectric conversion material.

[0005] Prior art literature

[0006] Patent Document 1: Japanese Patent No. 6127281

[0007] Patent Document 2: Japanese Patent Application Publication No. 2018-190953

[0008] Non-patent document 1: J. Shuai et al., “Significant Role of Mg Stoichiometry in Designing High Thermoelectric Performance for Mg3(Sb,Bi)2-Based n-Type Zintls”, J. Am. Chem. Soc. Vol. 140, pp. 1910-1915 (2018). [DOI: 10.1021 / jacs.7b12767] Summary of the invention

[0009] As can be understood from the above formula regarding the thermoelectric conversion performance index ZT, in a thermoelectric conversion material, the thermoelectric conversion efficiency decreases as the resistance value increases. In conventional thermoelectric conversion materials, the resistance value may increase over time depending on the surrounding environment.

[0010] The present invention provides a MgO-based material having a resistance value that is suppressed to change with time. 3 (Sb,Bi) 2 Department of thermoelectric conversion material.

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

[0012] A thermoelectric conversion material,

[0013] The thermoelectric conversion material is a polycrystalline material consisting of a plurality of crystal grains.

[0014] The composition of the thermoelectric conversion material is represented by formula (I): Mg 3+m Sb a Bi 2-a-c A c express,

[0015] in,

[0016] In the formula (I),

[0017] A is at least one element selected from Se and Te,

[0018] The value of m is 0.01 or more and 0.5 or less,

[0019] The value of a is greater than or equal to 0 and less than or equal to 1.0.

[0020] The value of c is 0.001 or more and 0.06 or less,

[0021] The thermoelectric conversion material has a Mg-rich portion.

[0022] According to the present disclosure, it is possible to realize MgO with suppressed temporal change in resistance value. 3 (Sb,Bi) 2 Department of thermoelectric conversion material. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram showing the crystal structure of crystal grains that can constitute the thermoelectric conversion material of the present disclosure.

[0024] Figure 2 It is a schematic diagram for explaining the distance d between two points in the RGB color space.

[0025] Figure 3 This is a schematic diagram showing an example of the thermoelectric conversion element of the present disclosure.

[0026] Figure 4 Yes means Figure 2 Schematic diagram of an example of the usage state of the thermoelectric conversion element.

[0027] Figure 5This is a graph showing an X-ray diffraction pattern of the thermoelectric conversion material prepared in Example 1.

[0028] Figure 6 For the thermoelectric conversion material having the same composition as that prepared in Example 1, La 2 O 3 Type crystal structure, showing the coordinate diagram of the simulated X-ray diffraction pattern.

[0029] Figure 7 An observation image of the surface of the thermoelectric conversion material produced in Example 1 observed using a scanning electron microscope (SEM) is shown.

[0030] Figure 8 This is a graph showing an energy dispersive X-ray spectroscopy (EDS) spectrum of the thermoelectric conversion material produced in Example 1.

[0031] Fig. 9 An image obtained by binarizing a quantitative analysis image of the surface of the thermoelectric conversion material produced in Example 1 is shown. DETAILED DESCRIPTION

[0032] (reference)

[0033] The Japanese Patent No. 6127281 is incorporated herein by reference.

[0034] (Embodiments of the present disclosure)

[0035] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0036] [Thermoelectric conversion materials]

[0037] The thermoelectric conversion material disclosed in the present invention is a polycrystalline material. The polycrystalline material is composed of a plurality of crystal grains. Each crystal grain constituting the thermoelectric conversion material disclosed in the present invention has La 2 O 3 Type crystal structure.

[0038] The composition of the thermoelectric conversion material disclosed in the present invention is represented by formula (I): Mg 3+m Sb a Bi 2-a-c A c In formula (I), A is at least one element selected from Se and Te. The value of m is greater than or equal to 0.01 and less than or equal to 0.5. The value of a is greater than or equal to 0 and less than or equal to 1.0. The value of c is greater than or equal to 0.001 and less than or equal to 0.06. The value of a may exceed 0.

[0039] Each crystal grain constituting the thermoelectric conversion material of the present disclosure has La 2 O 3 The crystal structure of the Figure 1In the crystal grains constituting the thermoelectric conversion material of the present disclosure, Mg is located in the La 2 O 3 The Sb, Bi and Te are located at site C1 of the type crystal structure, and the Te located at site C2. Te located at site C2 can also be replaced by Se within the above composition range.

[0040] The crystal grains constituting the thermoelectric conversion material disclosed herein can be observed by an enlarged observation image of the surface of the material. The surface is, for example, a cross-section of the thermoelectric conversion material. The enlarged observation image is, for example, an observation image using a SEM. Before obtaining the enlarged observation image, the surface can be polished. The crystal structure of the crystal grains can be confirmed by analysis based on an X-ray diffraction method.

[0041] The thermoelectric conversion material disclosed in the present invention has a Mg-enriched portion. A portion of the Mg-enriched portion is formed at the boundary of the grains. The Mg-enriched portion can be confirmed by quantitative analysis of an enlarged observation image of the material surface, such as an SEM observation image. Quantitative analysis can be performed, for example, by EDS combined with SEM (SEM / EDS). An example of a specific method for confirming the Mg-enriched portion by SEM / EDS is as follows.

[0042] An enlarged observation image of the evaluation object surface in the thermoelectric conversion material is obtained by SEM. Next, for the enlarged observation image, Mg, Sb, Bi, C and O elements are selected for quantitative analysis by EDS. Te with a trace content can be excluded from the selection. In addition, since there are cases where C and O are attached to the surface as impurities, they can also be applied selectively. Next, for the three elements Mg, Sb and Bi, the intensity is mapped corresponding to the concentration of each atom evaluated by quantitative analysis and displayed on an image. Furthermore, different colors are assigned to each element. The assigned colors are, for example, red (R) for Mg, green (G) for Sb and blue (B) for Bi. Next, a threshold is set for the purity of the color assigned to Mg, and the area with purity above the threshold on the mapping image is highlighted. The mapping image can be converted into a black and white binary image in which only the area with purity above the threshold is assigned white and represented. As an area with purity above the above threshold on the mapping image, it can be determined to be a Mg-rich Mg-rich area.

[0043] The color purity threshold can be set, for example, as follows. In the above mapping image where red is assigned to Mg, green is assigned to Sb, and blue is assigned to Bi, the ideal RGB value of the area consisting only of Mg is (R, G, B) = (255, 0, 0). Here, each RGB value is 256 grayscale. Figure 2As shown, in the RGB color space (i.e., color mapping), when the vector connecting the points of each element having a certain RGB and the origin is set to x, and the vector connecting the points of the element having (R, G, B) = (255, 0, 0) and the origin is set to y, the distance d between these two points in the color space is calculated by the following formula (1).

[0044]

[0045] If this d is used, the relative concentration C of Mg compared with Sb and Bi can be defined by the following formula (2). According to formula (2), the relative concentration C of Mg can be expressed in the range of 0 to 255. For the relative concentration C related to Mg, for example, 130 can be set as a threshold.

[0046]

[0047] The magnified observation image may be an image containing at least 10 grains. When the entire area of ​​the image is 600 μm 2 When the image is larger than 10, the image usually contains at least 10 grains.

[0048] The degree of formation of the Mg-enriched portion can be evaluated based on the ratio of the total area of ​​the Mg-enriched portion shown in the observation image to the overall area of ​​the enlarged observation image. Hereinafter, this ratio is recorded as the "Mg precipitation rate". The Mg precipitation rate can be obtained based on the above-mentioned mapping image in which the area with a purity above the threshold value of Mg is highlighted. The Mg precipitation rate is, for example, more than 1%. The upper limit of the Mg precipitation rate is, for example, less than 20%, less than 8%, and further less than 6%. The Mg precipitation rate is typically a value when the threshold value of the color purity is set by the above-mentioned method, and the threshold value based on the relative concentration C of Mg is set to 130.

[0049] In the past, it was believed that 3 (Sb,Bi) 2 When the composition ratio of Sb in the thermoelectric conversion material is small, the characteristics of the material including the resistance value are prone to change. However, in the thermoelectric conversion material disclosed in the present invention, the change of the resistance value over time can be suppressed even at a high temperature in a vacuum, for example. This change is usually increased. In the thermoelectric conversion material disclosed in the present invention, the resistance value before the heat resistance test implemented in a vacuum and placed at 450°C for 6 hours is set to R 0 The resistance value after the test is set as R 1 , by the formula: |(R 1 -R 0 ) / R 0 The resistance change rate obtained by |×100(%) is, for example, 250% or less, and may be 100% or less, 75% or less, 50% or less, 30% or less, or further 20% or less.

[0050] The thermoelectric conversion material of the present disclosure is generally n-type. As is well known to those skilled in the art in the technical field of thermoelectric conversion materials, n-type thermoelectric conversion materials have a negative Seebeck coefficient S.

[0051] The application of the thermoelectric conversion material disclosed in the present invention is not limited, and the application is, for example, a thermoelectric conversion element.

[0052] (Manufacturing method)

[0053] An example of a method for producing the thermoelectric conversion material disclosed in the present invention is shown below.

[0054] Mg powder, Sb powder, Bi powder and Te powder as raw materials are put into a grinding container for mechanical grinding. The grinding atmosphere is an inert gas atmosphere. The oxidation of the raw materials can be suppressed by this atmosphere. The inert gas is, for example, argon and / or helium. Through this process, a powder of a precursor alloy of MgSbBiTe can be obtained. Then, the obtained precursor alloy is sintered to obtain a polycrystal of MgSbBiTe. The sintering can be performed by, for example, a spark plasma sintering method. The obtained polycrystal can be used directly as a thermoelectric conversion material. In addition, the obtained polycrystal can also be subjected to heat treatment. In this case, the polycrystal after heat treatment can be used as a thermoelectric conversion material. When sintering is performed using a spark plasma method, insulation of the precursor alloy is usually ensured so that no current is applied to the precursor alloy provided for sintering. Insulation can be ensured, for example, by configuring an insulating material between the mold (sintering type) used in the spark plasma method and the precursor alloy.

[0055] [Thermoelectric conversion element]

[0056] An example of the thermoelectric conversion element disclosed in the present invention is shown in Figure 3 . Figure 3 The thermoelectric conversion element 10 includes a p-type thermoelectric conversion section 1, an n-type thermoelectric conversion section 2, a first electrode 3, a second electrode 4, and a third electrode 5. One end of the p-type thermoelectric conversion section 1 and one end of the n-type thermoelectric conversion section 2 are electrically connected to each other via the first electrode 3. The other end of the p-type thermoelectric conversion section 1 is electrically connected to the second electrode 4. The other end of the n-type thermoelectric conversion section 2 is electrically connected to the third electrode 5. The n-type thermoelectric conversion section 2 is composed of the thermoelectric conversion material disclosed in the present invention. In the thermoelectric conversion element 10, the time-dependent change in the resistance value in the n-type thermoelectric conversion section 2 is suppressed. As a result, a thermoelectric conversion element 10 having excellent characteristics, such as temporal stability of power generation, can be realized.

[0057] A method of using the thermoelectric conversion element 10 is shown in Figure 4 . Figure 4In the embodiment, the first wiring 6 is electrically connected to the second electrode 4 of the thermoelectric conversion element 10. In addition, the second wiring 7 is electrically connected to the third electrode 5. The first wiring 6 and the second wiring 7 play a role in taking out the electric power generated in the thermoelectric conversion element 10 to the outside.

[0058] Thermoelectric conversion element 10 can be manufactured by a known method.

[0059] The application of the thermoelectric conversion element of the present disclosure is not limited. The thermoelectric conversion element of the present disclosure can be used for various applications including the applications of conventional thermoelectric conversion elements.

[0060] Example

[0061] The thermoelectric conversion material of the present disclosure will be described in more detail below with reference to examples. However, the thermoelectric conversion material of the present disclosure is not limited to the embodiments shown in the following examples.

[0062] (Example 1)

[0063] (Preparation of MgSbBiTe Precursor Alloy)

[0064] 1.4008g of Mg powder, 1.3798g of Sb powder, 5.4863g of Bi powder and 0.0240g of Te powder were weighed as raw materials in a glove box. At least from the weighing of the raw materials to the obtaining of the thermoelectric conversion material, the interior of the glove box was controlled to an argon atmosphere. Then, each weighed powder was put into a ball mill container together with 2 stainless steel balls (diameter: 12.7mm) and 1 stainless steel ball (diameter: 6.35mm) in the glove box. The ball mill container is made of stainless steel and has an internal volume of 65mL. Then, the opening of the ball mill container is sealed in the glove box.

[0065] Next, the ball mill container was taken out of the glove box and placed in a ball mill. SPEX8000D from SPEX was selected as the ball mill. The ball mill was operated for 2 hours to form a powder of the MgSbBiTe precursor alloy.

[0066] (sintering)

[0067] Next, the ball mill container is moved to the inside of the glove box. In the glove box, the powder is taken out from the ball mill container. About 2.5g of the powder taken out is pressed into a cylinder with a diameter of 10mm. In the glove box, the cylinder is stored in the sintering space of a carbon mold (sintering type). The sintering space of the mold is cylindrical with a diameter of 15mm. The storage of the cylinder is implemented by filling insulating powder between the surface of the cylinder and the surface of the sintering space. By filling the insulating powder, insulation is ensured during sintering of the cylinder. Furthermore, as the insulating powder, a powder that is heat-resistant to the sintering temperature is selected.

[0068] Next, the mold is placed in the chamber of a spark plasma sintering device. The chamber is controlled to be an argon atmosphere. Next, while applying a pressure of 45 MPa to the cylinder and powder placed in the mold, an electric current is applied to the mold through the sintering device. By applying the electric current, the temperature of the mold reaches the sintering temperature, i.e., 800°C, and the temperature is maintained for 15 minutes. After that, the heating of the mold is stopped by gradually reducing the current. After the temperature of the mold drops to room temperature, the sintered body is removed from the mold. By grinding the surface of the sintered body, the above-mentioned insulating powder is removed from the sintered body. In this way, the thermoelectric conversion material of Example 1 is obtained.

[0069] (Example 2)

[0070] (Preparation of MgSbBiTe Precursor Alloy)

[0071] 2.0000g of Mg powder, 1.4734g of Sb powder, 7.5361g of Bi powder and 0.0309g of Te powder were weighed as raw materials in a glove box. At least from the weighing of the raw materials to the obtaining of the thermoelectric conversion material, the interior of the glove box was controlled to an argon atmosphere. Then, each weighed powder was put into a ball mill container together with 30 stainless steel balls (diameter: 10mm) in the glove box. The ball mill container is made of stainless steel and has an internal volume of 80mL. Then, the opening of the ball mill container was sealed in the glove box.

[0072] Next, the ball mill container was taken out of the glove box and placed on a planetary ball mill. As the planetary ball mill, a Pulverisette 6 manufactured by Fei Chi was selected. The planetary ball mill was operated to perform a pulverization process for 4 hours at a rotation speed of 400 rpm. The pulverization process formed a powder of the MgSbBiTe precursor alloy.

[0073] (sintering)

[0074] Next, the ball mill container is moved to the inside of the glove box. In the glove box, the powder is taken out from the ball mill container. About 2 g of the taken out powder is filled into the sintering space of the carbon mold in the glove box. The sintering space of the mold is cylindrical with a diameter of 10 mm. The storage of the powder is implemented by filling insulating powder between the powder and the surface of the sintering device. By filling the insulating powder, insulation is ensured during sintering of the precursor alloy. Furthermore, as the insulating powder, a powder that is heat-resistant to the sintering temperature is selected.

[0075] Next, the mold is placed in the chamber of a spark plasma sintering device. The chamber is controlled to be an argon atmosphere. Next, while applying a pressure of 50 MPa to the powder placed in the mold, an electric current is applied to the mold through the sintering device. By applying the electric current, the temperature of the mold reaches the sintering temperature, i.e., 750°C, and the temperature is maintained for 5 minutes. After that, the temperature of the mold is reduced to 600°C by reducing the current, and the temperature is maintained for 30 minutes. Next, the heating of the mold is stopped by stopping the current. After the temperature of the mold drops to room temperature, the sintered body is removed from the mold. By grinding the surface of the sintered body, the above-mentioned insulating powder is removed from the sintered body. In this way, the thermoelectric conversion material of Example 2 is obtained.

[0076] (Example 3)

[0077] (Preparation of MgSbBiTe Precursor Alloy)

[0078] A MgSbBiTe precursor alloy was prepared in the same manner as in Example 1 except that 1.5700 g of Mg powder, 2.2474 g of Sb powder, 3.8184 g of Bi powder, and 0.0024 g of Te powder were used as raw materials.

[0079] (sintering)

[0080] The thermoelectric conversion material of Example 3 was obtained in the same manner as in Example 2 except that the sintering temperature was changed to 600° C., the heating of the mold was stopped by stopping the current after maintaining the sintering temperature for 5 minutes, and the operation of maintaining at 600° C. for 30 minutes was not performed.

[0081] (Example 4)

[0082] (Preparation of MgBiTe Precursor Alloy)

[0083] A MgSbBiTe precursor alloy was prepared in the same manner as in Example 1 except that 1.3000 g of Mg powder, 6.1953 g of Bi powder, and 0.1169 g of Te powder were used as raw materials.

[0084] (sintering)

[0085] The thermoelectric conversion material of Example 4 was obtained in the same manner as in Example 2 except that the sintering temperature was changed to 550° C., the heating of the mold was stopped by stopping the current after maintaining the sintering temperature for 5 minutes, and the operation of maintaining at 600° C. for 30 minutes was not performed.

[0086] (Example 5)

[0087] (Preparation of MgSbBiTe Precursor Alloy)

[0088] A MgSbBiTe precursor alloy was prepared in the same manner as in Example 2 except that 2.0000 g of Mg powder, 1.8786 g of Sb powder, 7.5235 g of Bi powder, and 0.0328 g of Te powder were used as raw materials.

[0089] (sintering)

[0090] The sintering temperature was changed to 800°C, the holding time at the sintering temperature was changed to 15 minutes, the heating of the mold was stopped by stopping the current after maintaining at the sintering temperature, and the operation of maintaining at 600°C for 30 minutes was not implemented. Except for this, the thermoelectric conversion material of Example 5 was prepared in the same manner as Example 2.

[0091] (Evaluation of composition ratio)

[0092] The composition of each thermoelectric conversion material produced was evaluated by inductively coupled plasma (ICP) emission spectrometry. The evaluation results are shown in the following Table 1. As shown in Table 1, the composition of each thermoelectric conversion material was substantially the same as the charged composition of the raw material.

[0093] Table 1

[0094] Feed composition (molar ratio) Composition of thermoelectric conversion materials Example 1 <![CDATA[Mg 3.05 Sb 0.6 The 1.39 Whereas 0.01 ]]> <![CDATA[Mg 3.05 Sb 0.61 The 1.38 Whereas 0.011 ]]> Example 2 <![CDATA[Mg 3.4 Sb 0.5 The 1.49 Whereas 0.01 ]]> <![CDATA[Mg 3.39 Sb 0.5 The 1.50 Whereas 0.010 ]]> Example 3 <![CDATA[Mg 3.5 Sb 1.0 The 0.999 Whereas 0.001 ]]> <![CDATA[Mg 3.49 Sb 1.0 The 0.999 Whereas 0.001 ]]> Example 4 <![CDATA[Mg 3.5 Bi 1.94 You 0.06 ]]> <![CDATA[Mg 3.48 Bi 1.95 You 0.055 ]]> Example 5 <![CDATA[Mg 3.2 Sb 0.6 The 1.4 Whereas 0.01 ]]> <![CDATA[Mg 3.19 Sb 0.59 The 1.41 Whereas 0.009 ]]>

[0095] (Analysis of crystal structure)

[0096] The crystal structure of each of the produced thermoelectric conversion materials was analyzed by X-ray diffraction. CuKα rays were used for X-ray diffraction measurement. The lattice constants of the confirmed crystal structures are shown in Table 2.

[0097] Table 2

[0098]

[0099] The X-ray diffraction pattern of the thermoelectric conversion material of Example 1 is shown in Figure 5 In addition, for the thermoelectric conversion material having the same composition as that of Example 1, La 2 O 3 The simulated X-ray diffraction pattern of the crystal structure is shown in Figure 6 . Figure 5 The diffraction pattern of Figure 6 The diffraction patterns of are roughly the same. Therefore, it is confirmed that the thermoelectric conversion material of Example 1 has La 2 O 3 Similarly, it was confirmed that the thermoelectric conversion materials of Examples 2 to 5 also have La 2 O 3 Type crystal structure.

[0100] (Calculation of Seebeck coefficient)

[0101] The Seebeck coefficient S of each thermoelectric conversion material is shown in Table 3 below. For details on the calculation method of the Seebeck coefficient S, please refer to U.S. Patent Application No. 14 / 847,321 (International Application No.: PCT / JP2014 / 001882), U.S. Patent Application No. 14 / 847,362 (International Application No.: PCT / JP2014 / 001883) and U.S. Patent Application No. 14 / 718,491 (International Application No.: PCT / JP2014 / 001885). All three patent applications are cited in this application. As shown in Table 1, each thermoelectric conversion material is n-type.

[0102] Table 3

[0103]

[0104] (Observation of microstructure)

[0105] By observing the surface through SEM, it was confirmed that each of the produced thermoelectric conversion materials was a polycrystal composed of a plurality of crystal grains. The SEM magnified observation image of the surface of the thermoelectric conversion material of Example 1 is shown in FIG. Figure 7 Furthermore, Figure 7 The observed image is a reflected electron image. Before the SEM observation, the surface of the evaluation object was polished with polishing paper and argon beam. Figure 7 Shows the grain structure separated from each other by grain boundaries.

[0106] (Quantitative Analysis)

[0107] The above-mentioned quantitative analysis using SEM / XDS was performed on the prepared thermoelectric conversion material. Among the magnified observation images used in the quantitative analysis, images containing 10 or more crystal grains and having a short side of 25 μm or more were selected. ZAF correction was used in the quantitative analysis based on XDS. The XDS spectrum of the thermoelectric conversion material of Example 1 is shown in FIG. Figure 8 . The colors assigned to the mapping image are red for Mg, green for Sb, and blue for Bi. The threshold value of the color purity assigned to Mg is set by the above method. The threshold value set for the relative concentration C of Mg is 130. On the mapping image, the area with the threshold value of 130 or more is highlighted by the color assigned to Mg, i.e., red. Next, the obtained mapping image is converted into a black-and-white binary image in which only the area with Mg purity above the threshold value is assigned white. The binary image obtained by quantitative analysis of the thermoelectric conversion material of Example 1 is shown in FIG. Fig. 9 .like Fig. 9 As shown in FIG. 1 , a portion of the Mg-rich portion is formed at the boundary between the crystal grains of the thermoelectric conversion material. For the thermoelectric conversion material of Example 1, the Mg precipitation rate obtained from the above binary image is 1.44% (=11 μm2 / 762μm 2 × 100%). The evaluation results of quantitative analysis of each of the produced thermoelectric conversion materials are shown in Table 4 below.

[0108] Table 4

[0109]

[0110] (Evaluation of resistance value and rate of change)

[0111] The resistance value R of each thermoelectric conversion material was measured by the four-terminal method. 0 Next, each thermoelectric conversion material was kept at 450° C. for 6 hours in a vacuum, and then cooled to room temperature. The resistance value R was measured again using the four-terminal method. 1 . By the formula: |(R 1 -R 0 ) / R 0 | × 100 (%) The resistance change rate and resistance value R of each thermoelectric conversion material 0 and R 1 They are shown together in Table 5 below.

[0112] Table 5

[0113]

[0114] As shown in Tables 4 and 5, in the thermoelectric conversion materials of Examples 1 to 4 having a Mg precipitation rate of 1% or more, the resistance change rate was particularly small.

[0115] Industrial Applicability

[0116] The thermoelectric conversion material disclosed herein can be used for various applications including applications of conventional thermoelectric conversion materials.

[0117] Description of Reference Numerals

[0118] 1 p-type thermoelectric conversion unit

[0119] 2 n-type thermoelectric conversion unit

[0120] 3. 1st electrode

[0121] 4. Second electrode

[0122] 5. The third electrode

[0123] 6. 1st wiring

[0124] 7 Second wiring

[0125] 10 Thermoelectric conversion element

Claims

1. A thermoelectric conversion material, The thermoelectric conversion material is a polycrystalline material consisting of a plurality of crystal grains. The composition of the thermoelectric conversion material is represented by formula (I): Mg 3+m Sb a Bi 2-a-c A c It indicates that, In the formula (I), A is at least one element selected from Se and Te, The value of m is 0.01 or more and 0.5 or less, The value of a is greater than or equal to 0 and less than or equal to 1.

0. The value of c is 0.001 or more and 0.06 or less, The thermoelectric conversion material has a Mg-rich portion, A Mg-rich portion is formed at the boundary of the crystal grains.

2. The thermoelectric conversion material according to claim 1, Each of the crystal grains has a La2O3 type crystal structure.

3. The thermoelectric conversion material according to claim 1 or 2, The Mg precipitation rate is 1% or more.

4. The thermoelectric conversion material according to claim 3, The Mg precipitation rate is 20% or less.

5. The thermoelectric conversion material according to claim 3, The Mg precipitation rate is 8% or less.

6. The thermoelectric conversion material according to claim 1 or 2, The value of a is greater than 0 and less than or equal to 1.

0.

7. A thermoelectric conversion element comprising the following components: p-type thermoelectric conversion unit, n-type thermoelectric conversion unit, The first electrode, The second electrode, and The third electrode, in, One end of the p-type thermoelectric conversion portion and one end of the n-type thermoelectric conversion portion are electrically connected to each other via the first electrode. The other end of the p-type thermoelectric conversion portion is electrically connected to the second electrode, the other end of the n-type thermoelectric conversion portion is electrically connected to the third electrode, and, The n-type thermoelectric conversion section is composed of the thermoelectric conversion material according to any one of claims 1 to 4.

Images