JP2019161203A - Sulfide, thermoelectric conversion material, and thermoelectric conversion element - Google Patents

Abstract

To provide a sulfide which is small in the content of a typical metal element other than tin, and which has a low lattice thermal conductivity at 300 K.SOLUTION: A sulfide comprises copper, tin, and at least one typical metal element other than tin. The content of the copper to a total amount of metal included in the sulfide is 10 mol% or more. The content of the tin to the total amount of metal included in the sulfide is 10 mol% or more. The content of the typical metal element other than tin to the total amount of metal included in the sulfide is 10 mol% or more and 30 mol% or less. The sulfide has a lattice thermal conductivity of 1.3 W/(m K) or less at 300 K.SELECTED DRAWING: Figure 2A

Description

  The present invention relates to a sulfide, a thermoelectric conversion material, and a thermoelectric conversion element.

  In recent years, sulfides have attracted attention as semiconductor materials such as thermoelectric conversion materials and solar cell materials. A solar cell material is a material that absorbs light such as ultraviolet light, visible light, or infrared light, and converts light energy into electric energy by a photovoltaic effect. As solar cell materials, materials containing silicon or gallium arsenide have been put into practical use. On the other hand, in recent years, research on application of sulfide materials such as copper-indium-selenium sulfide (CIS) or copper-zinc-tin sulfide (CZTS) to solar cell materials is also active. These sulfide materials are expected to be safe and inexpensive solar cell materials, but compared to solar cell materials used for silicon solar cells, it is difficult to say that conversion efficiency is sufficient. Is required.

The thermoelectric conversion material is a material that generates a voltage by a temperature difference between both ends of the material by the Seebeck effect and converts thermal energy into electric energy, or generates a temperature difference by the electric energy by the Peltier effect. In recent years, sulfides containing copper and other metals have attracted attention as thermoelectric conversion materials. For example, Non-Patent Documents 1 and 2, respectively, the thermoelectric properties of the _{Cu 26 V 2 M 6 S 32} (M = Ge, Sn) and Cu ₂₆ V ₂ M ₆ S ₃₂ having a Korusaito structure having Korusaito structure Has been reported. Further, Patent Document 1 has a predetermined crystal structure, and is made of a composite metal sulfide containing, as a main component, copper and at least one metal other than copper, which is a first transition element or a p-block element. Thermoelectric conversion materials are described. In Non-Patent Document 3, the thermoelectric properties of Cu ₅ AlSn ₂ S ₈ in which Cu ₂ SnS ₃ is used as a parent structure and a part of Cu or Sn is replaced by Al are predicted by first-principles calculations. Specifically, Non-Patent Document 3 shows a calculation result for Configuration C (see FIG. 1), which is the most stable configuration of Cu ₅ AlSn ₂ S ₈ . According to the calculation result, the lattice thermal conductivity at 300 K of the sulfide having Configuration C is about 2.2 W / (m · K) (see Fig. 7).

Further, Non-Patent Document 4, the thermal conductivity of Cu ₂ Tl ₂ SnS ₄ is described to be 0.6W / (m · K) at 300K.

Non-patent documents 5 and 6 describe a method for synthesizing Cu ₃ AlSnS ₅ and Cu ₃ InSnS ₅ nanoparticles, respectively. According to Non-Patent Documents 5 and 6, the authors consider the application to solar cells and measure the ultraviolet-visible near-infrared absorption spectrum and current-voltage curve of these materials. However, Non-Patent Documents 5 and 6 do not describe measurement results regarding the thermal conductivity of Cu ₃ AlSnS ₅ and Cu ₃ InSnS ₅ .

JP 2016-48730 A

Applied Physics Letters, (US), 2014, Vol.105, 132107 Journal of Applied Physics, (US), 2014, Vol.116, 063706 Journal of Electronic Materials, (US), 2016, Vol. 45, No. 3, p.1453-1458 Chemistry of Materials, (US), 2005, Vol. 17, No. 11, p.2875-2884 ChemPlusChem, (Germany), 2015, Vol.80, 652-655 CrystEngComm, (English), 2013, Vol.15, p.10459-10463

According to the calculation result of Non-Patent Document 3, the lattice thermal conductivity at 300 K of Cu ₅ AlSn ₂ S ₈ having a stable configuration is calculated to be relatively high. Alternatively, there is a high possibility of replacing a part of Sn. Non-Patent Document 3 does not clarify the lattice thermal conductivity when Al irregularly substitutes a part of Cu or Sn. Although the sulfide of nonpatent literature 2 has comparatively low thermal conductivity in 300K, it needs to contain Tl (thallium) which has toxicity. Therefore, the present invention can also select a safer metal as a metal element other than copper and tin, by limiting the content of metal other than copper and tin in the sulfide to a predetermined value or less, More safely, it provides sulfides with low lattice thermal conductivity at 300K.

The present invention
A sulfide containing copper, tin, and at least one typical metal element other than tin,
The copper content in the total amount of metal contained in the sulfide is 10 mol% or more,
The tin content in the total amount of the metal is 10 mol% or more,
The content of the typical metal element in the total amount of the metal is 10 mol% or more and 30 mol% or less,
Having a lattice thermal conductivity of 1.3 W / (m · K) or less at 300 K;
Provide sulfide.

The present invention also provides:
A thermoelectric conversion material containing the sulfide is provided.

Furthermore, the present invention provides:
A thermoelectric conversion element provided with the thermoelectric conversion material is provided.

  The above sulfide has a small content of typical metal elements other than tin, and has a low lattice thermal conductivity at 300K.

FIG. 1A is a cross-sectional view showing an example of a thermoelectric conversion element according to the present invention. FIG. 1B is a cross-sectional view showing another example of the thermoelectric conversion element according to the present invention. FIG. 2A is a graph showing temperature changes of the thermal conductivity, carrier thermal conductivity, and lattice thermal conductivity of the sample according to Example 1. FIG. 2B is a graph showing the temperature change of the thermal conductivity, carrier thermal conductivity, and lattice thermal conductivity of the sample according to Example 2. FIG. 2C is a graph showing temperature changes of the thermal conductivity, carrier thermal conductivity, and lattice thermal conductivity of the sample according to Example 3. FIG. 2D is a graph showing changes in temperature of the thermal conductivity, carrier thermal conductivity, and lattice thermal conductivity of the sample according to Example 4. FIG. 3A is a graph showing temperature changes in electrical conductivity and electrical resistivity of the sample according to Example 1. FIG. 3B is a graph showing temperature changes in electrical conductivity and electrical resistivity of the sample according to Example 2. FIG. 3C is a graph showing temperature changes in electrical conductivity and electrical resistivity of the sample according to Example 3. FIG. 3D is a graph showing temperature changes in electrical conductivity and electrical resistivity of the sample according to Example 4. FIG. 4A is a graph showing temperature changes in Seebeck coefficient and power factor of the sample according to Example 1. FIG. 4B is a graph showing temperature changes in the Seebeck coefficient and power factor of the sample according to Example 2. FIG. 4C is a graph showing temperature changes in Seebeck coefficient and power factor of the sample according to Example 3. FIG. 4D is a graph showing temperature changes in Seebeck coefficient and power factor of the sample according to Example 4. FIG. 5A is a graph showing a dimensionless figure of merit of the sample according to Example 1. FIG. 5B is a graph showing a dimensionless figure of merit of the sample according to Example 2. FIG. 5C is a graph showing a dimensionless figure of merit of the sample according to Example 3. FIG. 5D is a graph showing a dimensionless figure of merit of the sample according to Example 4. 6A is a graph showing an X-ray diffraction pattern of a sample according to Example 1. FIG. 6B is a graph showing an X-ray diffraction pattern of a sample according to Example 2. FIG. FIG. 6C is a graph showing an X-ray diffraction pattern of the sample according to Example 3. 6D is a graph showing an X-ray diffraction pattern of a sample according to Example 4. FIG. FIG. 7 is a graph showing an X-ray diffraction pattern of the powder according to Example 4.

  The thermoelectric conversion material is a material that generates a voltage by the temperature difference between both ends of the material by the Seebeck effect and converts the heat energy into electric energy, or generates a temperature difference by the electric energy by the Peltier effect. As the thermoelectric conversion material, there are an n-type thermoelectric conversion material in which an electric current is generated by movement of electrons from a higher heat energy to a lower one, and a p-type thermoelectric conversion material in which an electric current is generated by movement of holes.

As an index indicating the performance of the thermoelectric conversion material, there is a dimensionless figure of merit ZT defined by the following formula (1). Here, S represents the Seebeck coefficient, σ represents electrical conductivity, T represents absolute temperature, and κ represents thermal conductivity. As shown in Equation (1), in order to increase the dimensionless figure of merit ZT, it is advantageous that the thermal conductivity κ is low.
ZT = S ² σT / κ (1)

On the other hand, the thermal conductivity κ is represented by the sum of the carrier thermal conductivity κcar and the lattice thermal conductivity κlat, as shown in the following formula (2). The carrier thermal conductivity κcar is expressed as in equation (3) known as Wiedemann-Franz law. Here, L is the Lorentz number and can be treated as a constant for a metal material, but is known to be smaller than a constant used for a metal material in a semiconductor material. Applied Physics Letters, ( U.S.), 2015, Vol. 3, 041506, it is proposed to define L as shown in equation (4). S in Formula (4) is a Seebeck coefficient.
κ = κcar + κlat (2)
κcar = LσT (3)
L = 1.5 + exp (-│S│ / 116) (4)

  Thus, when the carrier thermal conductivity κcar is low, the electrical conductivity σ also tends to be low, and the low carrier thermal conductivity κcar is not necessarily advantageous from the viewpoint of increasing the dimensionless figure of merit ZT. On the other hand, the lattice thermal conductivity κlat is not directly proportional to the electrical conductivity σ, and a low lattice thermal conductivity κlat is advantageous from the viewpoint of increasing the dimensionless figure of merit ZT.

According to the calculation result of Non-Patent Document 3, Cu ₅ AlSn ₂ S ₈ having a stable configuration shows a relatively high lattice thermal conductivity κlat at 300K. The reason for this is thought to be that light, which is a light element, vibrates greatly in the crystal lattice, so that heat is easily carried. In Non-Patent Document 3, the thermoelectric characteristics of Cu ₅ AlSn ₂ S ₈ are calculated based on the respective structures for configurations A, B, and C. However, the difference between the total energies of the configurations A, B, and C described in Non-Patent Document 3 is at most 0.004 eV. Therefore, the present inventors are not a structure constituted by any configuration described in Non-Patent Document 3, but a structure in which several configurations are combined, and Al is crystallized more randomly. It was thought that Cu ₅ AlSn ₂ S ₈ could be produced so as to have a structure arranged inside. If Al is randomly arranged in the crystal, the vibration of the entire crystal becomes incongruent, and the lattice thermal conductivity κlat of the crystal of Cu ₅ AlSn ₂ S ₈ having such a structure is non-patent document 3. It is thought that it will be lower than expected. In order for a certain element to exist randomly in the crystal as described above, it is preferable to take a number of metastable phase configurations as energy close to the most stable phase. The difference between these energies is preferably 0.03 eV or less, which is the thermal energy at room temperature, more preferably 0.01 eV or less, and still more preferably 0.005 eV or less.

Based on these ideas of the present inventors, the material capable of reducing the lattice thermal conductivity κlat is not limited to Cu ₅ AlSn ₂ S ₈ . Cu ₅ AlSn ₂ S ₈ has a composition in which Cu ₂ SnS ₃ and CuAlS ₂ are combined at a ratio of 2: 1 based on the amount of substances. Therefore, materials which combine Cu ₂ SnS ₃ and another material with a different ratio is likely to have a low lattice thermal conductivity Kappalat. In particular, if these two materials have similar crystal structures, the effect of having a low lattice thermal conductivity κlat may be enhanced. This is because, since the two materials have similar crystal structures, a variety of solid solution states can be taken even when the ratio of the solid solution changes, so that the randomness of the arrangement of specific elements such as Al can be improved. This is considered to be possible. In other words, it is preferable to use a combination of two or more materials having a wide solubility limit. Two materials having a similar crystal structure have a wide solid solution limit, and thus it is preferable to use such a material.

  Although the sulfide of Non-Patent Document 4 has a relatively low thermal conductivity at 300K, it needs to contain a relatively large amount of toxic Tl (thallium). Therefore, the present inventors can also select a safer metal as a metal element other than copper and tin, and limit the content of metals other than copper and tin in the sulfide to a predetermined value or less. Therefore, it was considered important to provide sulfides having a lower lattice thermal conductivity at 300K more safely.

  The inventors focused on sulfides containing typical metal elements other than copper, tin, and tin, and repeated a great deal of trial and error in order to develop sulfides having a low lattice thermal conductivity κlat. In addition, we tried to develop new sulfides, paying attention to reducing the content of typical metal elements other than tin in sulfides. As a result, the present inventors have newly found a sulfide having a small content of typical metal elements other than tin and having a low lattice thermal conductivity at 300K.

  Hereinafter, embodiments of the present invention will be described. The following description relates to an example of the present invention, and the present invention is not limited to these.

<Sulphides>
The sulfide according to the embodiment of the present invention includes copper, tin, and at least one typical metal element other than tin. The copper content in the total amount of metal contained in the sulfide is 10 mol% or more. The tin content in the total amount of metals contained in the sulfide is 10 mol% or more. The content of typical metal elements other than tin in the total amount of metals contained in the sulfide is 10 mol% or more and 30 mol% or less. For this reason, the content of typical metal elements other than tin in the total amount of metals contained in the sulfide is low. In addition, this sulfide has a lattice thermal conductivity of less than 1.3 W / (m · K) at 300K.

  The copper content in the total amount of metals contained in the sulfide may be, for example, 10 mol% or more, in some cases 30 mol% or more, and even 50 mol% or more. Moreover, the content rate of copper in the whole quantity of the metal contained in a sulfide is 80 mol% or less, for example. If the copper content in the total amount of metals contained in the sulfide is 10 mol% or more, the crystal structure of the sulfide is likely to be a zinc blende structure. Moreover, if the copper content in the total amount of metals contained in the sulfide is 30 mol% or more, the energy tends to be stable.

  The tin content in the total amount of metal contained in the sulfide may be, for example, 10 mol% or more, in some cases 15 mol% or more, and even 20 mol% or more. Further, the tin content in the total amount of metal contained in the sulfide is, for example, 80 mol% or less.

  In some cases, the tin content in the total amount of metal contained in the sulfide is desirably 22 mol% or more, and more desirably 25 mol% or more. On the other hand, the tin content in the total amount of metals contained in the sulfide is desirably 40 mol% or less. If the tin content in the total amount of metals contained in the sulfide is 22 mol% or more and 40 mol% or less, the crystal structure of the sulfide tends to be a zinc blende structure. Furthermore, if the tin content in the total amount of metal contained in the sulfide is 25 mol% or more, the number of configurations that the sulfide can take increases, and the thermal conductivity of the sulfide can be easily reduced.

  The content of typical metal elements other than tin in the total amount of metals contained in the sulfide is desirably 10 mol% or more, and more desirably 12 mol% or more. The content of typical metal elements other than tin in the total amount of metals contained in the sulfide is desirably 30 mol% or less, and more desirably 25 mol% or less. If the content of typical metal elements other than tin in the total amount of metals contained in the sulfide is 10 mol% or more, there is a sufficient amount of typical metal elements to replace copper or tin. If the content of the typical metal element other than tin in the total amount of metals contained in the sulfide is 30 mol% or less, the sulfide can have various crystal structures, and thus more types of materials can be provided.

  In some cases, the content of typical metal elements other than tin in the total amount of metals contained in the sulfide is desirably 18 mol% or less, and more desirably 15 mol% or less. If the content of typical metal elements other than tin in the total amount of metals contained in the sulfide is 18 mol% or less, the typical metal elements other than tin in the sulfide are regularly arranged in the crystal structure. An increase in thermal conductivity can be suppressed. Furthermore, if the content of the typical metal element other than tin in the total amount of the metal contained in the sulfide is 15 mol% or less, the typical metal element other than tin can be present in the structure more randomly. The lattice thermal conductivity can be reduced efficiently.

In the sulfide, the following conditions (I) and (II) are preferably satisfied in some cases.
(I) The tin content in the total amount of metal contained in the sulfide is 22 mol% or more and 40 mol% or less.
(II) The content of typical metal elements other than tin in the total amount of metals contained in the sulfide is 10 mol% or more and 18 mol% or less.

When the sulfide satisfies the above conditions (I) and (II), it preferably further satisfies the following condition (III).
(III) The copper content in the total amount of metal contained in the sulfide is 42 mol% or more and 68 mol% or less.

  When the sulfide satisfies the conditions (I) to (III), the copper content in the total amount of metals contained in the sulfide is more preferably 62% or more.

  The sulfide may contain two or more kinds of typical metal elements as typical metal elements other than tin. In this case, the content rate of the typical metal elements other than tin in the total amount of the metal contained in the sulfide is the sum of the content rates of the respective types of typical metal elements.

  The typical metal element other than tin contained in the sulfide is desirably trivalent. Thereby, content of typical metal elements other than tin in sulfide tends to be low. Thallium often behaves as a monovalent.

  The typical metal element other than tin contained in the sulfide is desirably at least one of Al and In. In this case, the lattice thermal conductivity of sulfide at 300K is more surely low.

The sulfide desirably has a composition represented by Cu ₅ Al _x In _1-x Sn ₂ S ₈ . Here, x is 0-1. In this case, the lattice thermal conductivity of sulfide at 300K is more surely low.

  The sulfide desirably has a crystal structure in which mainly anions are arranged in a tetrahedral shape. Examples of the structure in which the anions are arranged in a tetrahedral shape include crystal structures such as a zinc blende structure, a wurtzite structure, and an inverted fluorite structure. The sulfide more desirably has at least one crystal structure of a zinc blende structure and a wurtzite structure, and more desirably has a zinc blende structure. The zinc-blende-type crystal structure is a structure in which the cubic close-packed lattice of anions is expanded, and half of the voids of the tetrahedron made of anions are occupied by cations. Therefore, even if the cation site is substituted with an element having a different size in the zinc blende type crystal structure, the remaining half of the void not occupied by the cation buffers the distortion of the structure. For this reason, it is considered that an element of a specific ratio or less can replace the cation in the zinc blende type crystal structure. In addition, the zincblende structure has a higher electric conductivity than the sulfide having a thiospinel-type crystal structure composed of the same elements, and has advantageous characteristics as a thermoelectric conversion material. Examples of the structure similar to the zinc blende type include structures such as a corusite type structure, a germanite type structure, a stannite type structure, and a kesterite type structure. These structures are also structures in which anions are arranged in a tetrahedral shape.

  The sulfide may contain a different metal from copper, tin, and a typical metal element other than tin. The dissimilar metal content in the total amount of metals contained in the sulfide is, for example, 5 mol% or less, desirably 3 mol% or less, and more desirably 1 mol% or less. It is particularly desirable that the sulfide is substantially free of foreign metals. Thereby, the lattice thermal conductivity of sulfide at 300K can be reduced more reliably. In the present specification, “substantially does not contain” means that a foreign metal is intentionally not contained unless the foreign metal is inevitably mixed for production reasons such as raw materials or production equipment. means.

  The sulfide can be produced, for example, by sintering a powder obtained by mixing a copper powder, a tin powder, a powder of a typical metal element other than tin, and a sulfur powder. For mixing these powders, for example, a known apparatus such as a ball mill can be used. The method for sintering the powder is, for example, spark plasma sintering or hot pressing. The sintering temperature is, for example, 150 ° C. to 1500 ° C., and desirably 200 ° C. to 1000 ° C. The sintering time is, for example, 0 minutes to 10 minutes, and preferably 0 to 5 minutes. Moreover, the temperature increase time required from the start of a sintering process until it reaches the maximum temperature in a sintering process is 2 minutes-10 minutes, for example. For example, the temperature inside the die filled with powder is raised to the maximum temperature during the above temperature rise time, the temperature inside the die is kept at the maximum temperature for a predetermined time (sintering time), and then heating is stopped. Then, the sintered body is naturally cooled. The pressure for pressing the powder during the sintering process is, for example, 0.5 MPa to 100 MPa, and desirably 5 MPa to 50 MPa. When the size of the pellet is large or when it is necessary to increase the mechanical strength of the pellet, it is preferable to further increase the sintering time or the temperature raising time in order to obtain a uniform sintered body. This sintering step can be performed in an inert gas atmosphere or a vacuum atmosphere. This sintering step is desirably performed in a vacuum atmosphere.

  The above sulfides may be synthesized by a method such as a melting method, a hydrothermal synthesis method, or a liquid phase reduction method. In particular, a sulfide particle of nanometer order (for example, having a particle size of 100 nm or less) synthesized by a liquid phase reduction method efficiently scatters phonons by adjusting the particle size, resulting in a low lattice. It is expected to show thermal conductivity.

  The melting method is a method of obtaining a target compound by reacting raw materials at a high temperature. An example of a melting method is a method in which a raw material is vacuum-sealed in a quartz tube or the like so as to have a substance amount ratio of a target material, and the raw material is reacted at a predetermined reaction temperature using a heating device such as an electric furnace It is.

An example of the hydrothermal synthesis method will be described. A mixed solution is prepared by adding a copper compound, a tin compound, a typical metal element other than tin, and a sulfur compound or simple sulfur to water so as to obtain a substance amount ratio of the target material, and mixing them in water. Next, hydrothermal synthesis is performed by placing the mixed solution in an environment having a temperature of 150 to 300 ° C. and a pressure of 0.5 to 9 MPa (megapascal) for a predetermined period. The copper compound in this manufacturing method is, for example, chloride such as CuCl and CuCl _2, copper nitrate such as Cu (NO ₃ ) ₂ , or copper acetate such as Cu (CH ₃ COO) and Cu (CH ₃ COO) _2. is there. The tin compound in this production method is, for example, chlorides such as SnCl ₂ and SnCl ₄ , tin nitrate, or tin acetate. The sulfur compound in this production method is, for example, an organic sulfur compound such as thiourea and thioacetamide. For typical metal elements other than tin, for example, compounds such as chlorides, nitrates, and acetates can be used as a supply source of the metal elements.

  An example of the liquid phase reduction method will be described. First, typical metal elements other than copper compounds, tin compounds, and tin in the organic solvent so that the content of typical metal elements other than copper, tin, and tin in the total amount of metal contained in the sulfide is in the above range. And a mixed solution containing a sulfur compound and / or simple sulfur. Preparation of a liquid mixture is performed in the environment of normal temperature and a normal pressure, for example. Next, the liquid mixture is placed in an environment filled with an inert gas at a temperature of 150 to 350 ° C. for a predetermined period to synthesize a thermoelectric conversion material.

In this method, the copper compound include, for example, (i) chlorides such as CuCl and _{CuCl 2, (ii) Cu (} NO 3) ₂ and the like copper _{nitrate, (iii) Cu (CH 3} COO), Cu (CH 3 COO) ₂ and a carboxylate copper such as copper neodecanoate, or (iv) a complex compound such as copper acetylacetonate soluble in an organic solvent. In this method, the tin compound is a complex compound such as a chloride such as SnCl ₂ and SnCl ₄ , tin nitrate, tin carboxylate, and tin acetylacetonate. In this method, the compound of a typical metal element other than tin is, for example, a chloride, a nitric acid compound, a carboxylic acid compound, or a complex compound such as acetylacetonate of the typical metal element. In this method, the sulfur compound is, for example, (i) thiol such as octanethiol, decanethiol, and dodecanethiol, (ii) dithiol such as octanedithiol, decanedithiol, and dodecanedithiol, (iii) thiourea, or ( iv) Organic sulfur compounds such as thioacetamide. The organic sulfur compound is desirably a liquid organic sulfur compound such as thiol. In this case, the liquid organic sulfur compound can serve as an organic solvent in the mixed solution. The liquid mixture may contain a liquid organic compound other than the liquid organic sulfur compound. Examples of such liquid organic compounds include (i) amines such as oleylamine, (ii) unsaturated fatty acids such as myristoleic acid, palmitoleic acid, and oleic acid, or (iii) ethylene glycol, triethylene glycol, and Mention may be made of polyhydric alcohols such as tetraethylene glycol.

  The inert gas used in this method is not particularly limited as long as it is inert with respect to the mixed solution, and is, for example, a rare gas such as argon or nitrogen. The pressure in the environment where the liquid mixture is placed is desirably normal pressure.

  In this manufacturing method, the period for maintaining the environment of 150 to 350 ° C. filled with the inert gas is, for example, 1 to 5 hours.

<Thermoelectric conversion material>
This sulfide has a low lattice thermal conductivity at 300K, and this sulfide has advantageous properties for thermoelectric conversion materials. For this reason, the thermoelectric conversion material which concerns on this invention contains said sulfide. The thermoelectric conversion material may be comprised only from this sulfide, and may further contain another component with this sulfide. In addition, there is a possibility that this sulfide can be used for applications other than thermoelectric conversion materials. For example, this sulfide may be used as a material for solar cells.

<Thermoelectric conversion element>
A thermoelectric conversion element can be produced using the thermoelectric conversion material containing the sulfide. In this case, the thermoelectric conversion element includes a thermoelectric conversion material containing the sulfide.

  For example, a thermoelectric conversion element includes a thermoelectric conversion material containing the above sulfide and a conductor connected to the thermoelectric conversion material. As shown in FIG. 1A, the thermoelectric conversion element 1 includes, for example, a plurality of first thermoelectric conversion materials 10 and a plurality of second thermoelectric conversion materials 20 arranged alternately with the first thermoelectric conversion materials 10 and first adjacent to each other. A conductor 30 that connects the thermoelectric conversion material 10 and the second thermoelectric conversion material 20 is provided. For example, the plurality of first thermoelectric conversion materials 10 and the plurality of second thermoelectric conversion materials 20 are connected in series by a conductor 30. The first thermoelectric conversion material 10 is a thermoelectric conversion material containing the above sulfide. On the other hand, the second thermoelectric conversion material 20 is a known n-type semiconductor that can be used for a thermoelectric conversion element. As shown in FIG. 1A, the conductor 30 is disposed, for example, on a predetermined substrate 40a or substrate 40b. Each of the substrate 40a and the substrate 40b is a ceramic substrate having a high thermal conductivity, for example.

  As shown in FIG. 1B, the thermoelectric conversion element 2 includes, for example, a plurality of first thermoelectric conversion materials 50 and a conductor 60 that connects the adjacent first thermoelectric conversion materials 50. For example, the plurality of first thermoelectric conversion materials 50 are connected in series by the conductor 60. The first thermoelectric conversion material 50 is a thermoelectric conversion material containing the above sulfide. As shown in FIG. 1B, the conductor 60 is disposed on, for example, a predetermined substrate 70a or substrate 70b. Each of the substrate 70a and the substrate 70b is, for example, a ceramic substrate having high thermal conductivity.

  Hereinafter, the present invention will be described in more detail with reference to examples. The following examples are examples of the present invention, and the present invention is not limited to the following examples.

<Example 1>
1.137 g of copper powder, 0.097 g of aluminum powder, 0.849 g of tin powder and 0.918 g of sulfur powder were charged into a planetary ball mill manufactured by Lecce and rotated for 9 minutes at 400 rpm (revolutions per minute). The operation of stopping for 1 minute was repeated for 3 hours to obtain a powder. The obtained powder was sintered by a discharge plasma sintering apparatus (manufactured by Sinterland, model number: LABOX-125). In this sintering, a die having a diameter of 10 mm is filled with 0.75 g of powder, the temperature inside the die is increased to 800 ° C. at a rate of 100 ° C./minute, and then the temperature inside the die is increased to 2 ° C. at 800 ° C. Made by keeping minutes. Thereafter, both surfaces of the pellets, which are sintered products taken out from the inside of the die, were polished using abrasive paper having a particle size of # 2000 based on JIS R 6001: 1998, and a sample according to Example 1 was obtained.

<Example 2>
Example 1 except that 1.029 g of copper powder, 0.372 g of aluminum powder, 0.759 g of tin powder, and 0.831 g of sulfur powder were used and the sintering temperature was changed to 600 ° C. A sample according to Example 2 was obtained.

<Example 3>
Implementation as in Example 1 except that 1.080 g of copper powder, 0.046 g of aluminum powder, 0.195 g of indium powder, 0.807 g of tin powder and 0.872 g of sulfur were used. A sample according to Example 3 was obtained.

<Example 4>
20 mmol of neodecanoic acid copper, 4 mmol of indium 2-ethylhexanoate, 8 mmol of tin 2-ethylhexanoate, 100 ml of dodecanethiol, and 100 ml of oleylamine were mixed and stirred to obtain a uniformly dispersed mixture A. Next, a container containing the mixed solution A was placed in a space filled with argon gas, and the mixed solution A was stirred for 3 hours while being heated to 260 ° C., thereby obtaining a liquid in which particles were deposited. Methanol was added to the liquid thus obtained and centrifuged at 5000 rpm for 5 minutes to collect precipitates. The collected precipitate was washed with hexane and methanol. Thereafter, the obtained precipitate is dispersed in 50 ml of toluene, this dispersion is mixed with a solution of 2.5 g of thiourea dissolved in methanol, the mixture is subjected to ultrasonic treatment, and the surface treatment agent is added. Replaced. Thereafter, the solid was washed with hexane, methanol, and toluene, and further, the solid was vacuum dried using a vacuum dryer. Thus, the powder which concerns on Example 4 was obtained. The powder according to Example 4 was sintered and polished in the same manner as in Example 1 except that the sintering temperature was changed to 600 ° C., and a sample according to Example 4 was obtained.

<Measurement of thermal conductivity>
Thermal conductivity at a plurality of temperatures in the range of 300 to 700K was measured using the samples according to Examples 1 to 4. For the measurement of thermal conductivity, a laser flash method thermophysical property measuring apparatus (manufactured by Kyoto Electronics Industry Co., Ltd., product name: LFA-502) was used. The results are shown in FIGS. 2A to 2D.

<Measurement of electrical conductivity and Seebeck coefficient>
Electrical conductivity σ of the samples according to Examples 1 to 4 using a thermoelectric property evaluation apparatus (manufactured by Ozawa Science Co., Ltd., product name: RZ2001i) or a thermoelectric property evaluation apparatus (manufactured by ULVAC-RIKO, Inc., product name: ZEM-3) Was measured. This measurement was performed several times. The results are shown in FIGS. 3A to 3D. In addition, the electrical resistivity (rho) was calculated | required taking the reciprocal number of the electrical conductivity (sigma) of the sample which concerns on Examples 1-4. The results are shown in FIGS. 3A to 3D. The Seebeck coefficient S of the sample which concerns on Examples 1-4 was measured using said thermoelectric characteristic evaluation apparatus. The results are shown in FIGS. 4A to 4D. In the samples according to Examples 1 to 4, the power factor PF was obtained from the Seebeck coefficient S and the electrical conductivity σ based on the following formula (5). The results are shown in FIGS. 4A to 4D.
PF = S ² σ (5)

<Determination of carrier thermal conductivity and lattice thermal conductivity>
From the measurement result of the Seebeck coefficient S regarding the samples according to Examples 1 to 4, the Lorentz number L was determined using the above equation (4). From the determined measurement results of the Lorentz number L and the electrical conductivity σ, the carrier thermal conductivity κcar at the measurement temperature of the thermal conductivity of the samples according to Examples 1 to 4 was calculated using the above formula (3). The lattice thermal conductivity κlat at the measurement temperature of the thermal conductivity of the samples according to Examples 1 to 4 was determined by subtracting the carrier thermal conductivity κcar from the thermal conductivity according to the equation (2). The results are shown in FIGS. 2A to 2D. As shown in FIGS. 2A to 2D, the samples according to Examples 1 to 4 had a lattice thermal conductivity of 300 W or less at 1.3 W / (m · K).

<Dimensionless performance index>
From the results shown in FIGS. 2A to 2D, FIGS. 3A to 3D, and FIGS. 4A to 4D, the dimensionless figure of merit ZT for the samples according to Examples 1 to 4 was obtained. The results are shown in FIGS. 5A to 5D.

<X-ray diffraction measurement>
Using an X-ray diffractometer (product name: MiniFlex600, manufactured by Rigaku Corporation), an X-ray diffraction pattern of the sample after sintering by spark plasma sintering according to Examples 1 to 4 was obtained. CuKα rays were used as X-rays. The X-ray diffraction patterns of the samples according to Examples 1 to 4 are shown in FIGS. 6A to 6D.

  Using an X-ray diffractometer (product name: MiniFlex600, manufactured by Rigaku Corporation), an X-ray diffraction pattern of the powder before sintering by spark plasma sintering according to Example 4 was obtained. CuKα rays were used as X-rays. The X-ray diffraction pattern of the powder according to Example 4 is shown in FIG. It was suggested that the powder before sintering by spark plasma sintering according to Example 4 has a wurtzite structure type crystal structure.

Using a high frequency inductively coupled plasma optical emission spectrometry (ICP-OES) apparatus (manufactured by Thermo Fisher Scientific, product name: iCAP 6500), the metal element composition of the powder before sintering by spark plasma sintering according to Example 4 was used. analyzed. As a pretreatment for analysis, the powder was dissolved in a hydrochloric acid solution using a microwave heating acid decomposition apparatus (product name: ETHOS UP, manufactured by Milestone General). As a result of the analysis, the Cu content, the In content, and the Sn content in the total metal components of the powder before sintering by spark plasma sintering according to Example 4 are 62. 5%, 12.5%, and 25%. It was suggested that the powder before sintering by spark plasma sintering according to Example 4 has a composition represented by Cu ₅ InSn ₂ S ₈ .

Claims (5)

A sulfide containing copper, tin, and at least one typical metal element other than tin,
The copper content in the total amount of metal contained in the sulfide is 10 mol% or more,
The tin content in the total amount of the metal is 10 mol% or more,
The content of the typical metal element in the total amount of the metal is 10 mol% or more and 30 mol% or less,
Having a lattice thermal conductivity of 1.3 W / (m · K) or less at 300 K;
Sulfide.   The sulfide according to claim 1, wherein the content of the typical metal element in the total amount of the metal is 18 mol% or less. _{Cu 5 Al x In 1-x} Sn 2 having a composition represented by S _8, x is 0-1, sulfide according to claim 1 or 2.   The thermoelectric conversion material containing the sulfide of any one of Claims 1-3.   A thermoelectric conversion element comprising the thermoelectric conversion material according to claim 4.

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