JP7290915B2 - Sulfides, thermoelectric conversion materials, and thermoelectric conversion elements - Google Patents

Description

The present invention relates to sulfides, thermoelectric conversion materials, and thermoelectric conversion elements.

In recent years, sulfides have attracted particular 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 electrical energy by the photovoltaic effect. Materials containing silicon, gallium arsenide, or the like have been put to practical use as solar cell materials. On the other hand, in recent years, there has been active research into the application of sulfide materials such as copper-indium-selenium sulfide (CIS) or copper-zinc-tin sulfide (CZTS) to solar cell materials. These sulfide materials are expected to be safe and inexpensive solar cell materials. is required.

A thermoelectric conversion material is a material that generates a voltage due to a temperature difference across the material due to the Seebeck effect and converts thermal energy into electrical energy, or that generates a temperature difference due to electrical energy due to 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 describe thermoelectric properties of Cu ₂₆ V ₂ M ₆ S ₃₂ (M=Ge, Sn) having a colusite structure and Cu ₂₆ V ₂ M ₆ S ₃₂ having a colusite structure, respectively. has been reported. In addition, in Patent Document 1, a composite metal sulfide having a predetermined crystal structure and containing copper and at least one metal other than copper, which is a first transition element or p-block element, as main components , thermoelectric conversion materials are described. In addition, in Non-Patent Document 3, the thermoelectric properties of _{Cu5AlSn2S8 in which Cu2SnS3} is used as the base structure and part of Cu or _Sn is replaced with Al are predicted by first-principles calculation.

Non-Patent Documents 4, 5, and 6 include Cu ₂ Tl ₂ SnS ₄ , Cu ₄ In _x Sn _1-x S ₄ (x=0-0.02), and copper, zinc, and tin, respectively. Thermoelectric properties of sulfides (CZTS) have been reported.

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, (USA), 2016, Vol. 45, No.3, p. 1453-1458 Chemistry of Materials, (US), 2005, Vol.17, No. 11, p.2875-2884 The Journal of Electronic Materials, (US), 2014, Vol. 43, No. 6, p. 2202-2205 Nano Letters, (US), 2012, Vol. 12, No. 2, p. 540-545

According to Non-Patent Documents 1 to 6, the thermoelectric properties of sulfides containing copper, tin, and typical metal elements other than tin, in which at least one of these metals is replaced with a transition metal element, are not clear. Therefore, the present invention provides a novel sulfide containing copper, tin, and typical metal elements other than tin, wherein at least one of these metals is replaced with a transition metal element, and having advantageous properties as a thermoelectric conversion material. .

The present invention
A sulfide containing copper, tin, at least one typical metal element other than tin, and at least one transition metal element,
The content of copper in the total amount of metals contained in the sulfide is 10 mol% or more,
The content of the tin 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,
The content of the transition metal element in the total amount of the metal is 10 mol% or less,
The transition metal element replaces at least one of the copper, the tin, and the typical metal element,
Provides sulfide.

In addition, the present invention
A thermoelectric conversion material containing the above sulfide is provided.

Furthermore, the present invention provides
Provided is a thermoelectric conversion element comprising the above thermoelectric conversion material.

The above sulfides have advantageous properties as thermoelectric conversion materials.

FIG. 1A is a cross-sectional view showing one 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. 2A is a graph showing changes in electrical conductivity and electrical resistivity with temperature of a sample according to Example 1. FIG. 2B is a graph showing changes in electrical conductivity and electrical resistivity with temperature of the sample according to Example 2. FIG. 2C is a graph showing changes in electrical conductivity and electrical resistivity with temperature of the sample according to Example 3. FIG. 2D is a graph showing changes in electrical conductivity and electrical resistivity with temperature of the sample according to Example 4. FIG. 2E is a graph showing changes in electrical conductivity and electrical resistivity with temperature of the sample according to Example 5. FIG. 2F is a graph showing changes in electrical conductivity and electrical resistivity with temperature of the sample according to Example 6. FIG. 2G is a graph showing changes in electrical conductivity and electrical resistivity with temperature of the sample according to Example 7. FIG. 2H is a graph showing the temperature change of the electrical conductivity and electrical resistivity of the sample according to Example 8. FIG. 2I is a graph showing changes in electrical conductivity and electrical resistivity with temperature of the sample according to Example 9. FIG. 3A is a graph showing the temperature change of the Seebeck coefficient and power factor of the sample according to Example 1. FIG. 3B is a graph showing the temperature change of the Seebeck coefficient and power factor of the sample according to Example 2. FIG. 3C is a graph showing the temperature change of the Seebeck coefficient and power factor of the sample according to Example 3. FIG. 3D is a graph showing the temperature change of the Seebeck coefficient and power factor of the sample according to Example 4. FIG. 3E is a graph showing the temperature change of the Seebeck coefficient and power factor of the sample according to Example 5. FIG. 3F is a graph showing the temperature change of the Seebeck coefficient and power factor of the sample according to Example 6. FIG. 3G is a graph showing the temperature change of the Seebeck coefficient and power factor of the sample according to Example 7. FIG. 3H is a graph showing the temperature change of the Seebeck coefficient and power factor of the sample according to Example 8. FIG. 3I is a graph showing the temperature variation of the Seebeck coefficient and power factor of the sample according to Example 9. FIG. FIG. 4 is a graph showing the temperature change of the power factor of the samples according to Examples 1 to 5 and the sample according to the reference example. 5A is a graph showing an X-ray diffraction pattern of a sample according to Example 1. FIG. 5B is a graph showing the X-ray diffraction pattern of the sample according to Example 2. FIG. 5C is a graph showing the X-ray diffraction pattern of the sample according to Example 3. FIG. 5D is a graph showing the X-ray diffraction pattern of the sample according to Example 4. FIG. 5E is a graph showing the X-ray diffraction pattern of the sample according to Example 5. FIG. 5F is a graph showing the X-ray diffraction pattern of the sample according to Example 6. FIG. 5G is a graph showing the X-ray diffraction pattern of the sample according to Example 7. FIG. 5H is a graph showing the X-ray diffraction pattern of the sample according to Example 8. FIG. 5I is a graph showing the X-ray diffraction pattern of the sample according to Example 9. FIG.

A thermoelectric conversion material is a material that converts thermal energy into electrical energy by generating a voltage due to a temperature difference across the material by the Seebeck effect, or that generates a temperature difference by electrical energy by the Peltier effect. Thermoelectric conversion materials include n-type thermoelectric conversion materials in which current is generated by movement of electrons from higher to lower thermal energy, and p-type thermoelectric conversion materials in which current is generated by movement of holes.

As an index for evaluating the performance of thermoelectric conversion materials, there is a dimensionless figure of merit ZT defined by the following formula (1). Here, S indicates the Seebeck coefficient, σ indicates electrical conductivity, T indicates absolute temperature, and κ indicates thermal conductivity. It is desirable that the thermoelectric conversion material has a high dimensionless figure of merit ZT.
ZT=S ² σT/κ (1)

Moreover, there is a power factor PF represented by the following formula (2) as an index for evaluating the performance of thermoelectric conversion materials. A high power factor PF is advantageous in increasing the dimensionless figure of merit ZT.
PF=S ² σ (2)

The present inventors focused on copper, tin, and sulfides containing typical metal elements other than tin, and after much trial and error, tried to replace these metals with predetermined metals. As a result, we have newly found a sulfide that has advantageous properties as a thermoelectric conversion material.

Embodiments of the present invention will be described below. In addition, the following description relates to an example of the present invention, and the present invention is not limited to these.

<Sulfide>
A sulfide according to an embodiment of the present invention contains copper, tin, at least one typical metal element other than tin, and at least one transition metal element. The content of copper in the total amount of metals contained in this sulfide is 10 mol % or more. The content of tin 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. The transition metal element replaces at least one of copper, tin, and typical metal elements other than tin. The transition metal element content in the total amount of metals contained in the sulfide is 10 mol % or less.

The content of copper in the total amount of metals contained in the sulfide can be, for example, 10 mol % or more, in some cases 30 mol % or more, and further 50 mol % or more. Moreover, the content of copper in the total amount of metals contained in the sulfide is, for example, 70 mol % or less. If the content of copper in the total amount of metals contained in the sulfide is 10 mol % or more, the crystal structure of the sulfide tends to be a zincblende structure. Moreover, when the copper content in the total amount of metals contained in the sulfide is 30 mol % or more, the sulfide tends to be stable in terms of energy.

The tin content in the total amount of metals contained in the sulfide can be, for example, 10 mol % or more, in some cases 15 mol % or more, or even 20 mol % or more. Also, the content of tin in the total amount of metals contained in the sulfide is, for example, 70 mol % or less.

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, 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, 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 30 mol% or less, the lattice thermal conductivity is increased by regularly arranging the typical metal elements other than tin in the sulfide. You can control the increase.

The sulfide may contain two or more types of typical metal elements other than tin. In this case, the content of typical metal elements other than tin in the total amount of metals contained in the sulfide is the sum of the content of each type of typical metal element.

A typical metal element other than tin contained in the sulfide is desirably trivalent.

A typical metal element other than tin contained in the sulfide is desirably at least one of Al and In. In this case, the sulfide tends to have desired properties as a thermoelectric conversion material.

The sulfide may contain two or more transition metal elements as transition metal elements substituting at least one of copper, tin, and typical metal elements other than tin. In this case, the content of the transition metal element in the total amount of metal contained in the sulfide is the sum of the content of each type of transition metal element.

The sulfide desirably has a composition represented by Cu5 _{- aAlxbIn1 - xcSn2-} dDa _{+b+c+ dS8} . Here, D is the above transition metal element that substitutes for at least one of copper, tin, and typical metal elements other than tin. In addition, this sulfide satisfies the relationships 0≤x≤1 and 0<a+b+c+d≤0.8. In this case, the sulfide tends to have desired properties as a thermoelectric conversion material.

Sulfide more preferably satisfies the relationship 0<a+b+c+d≦0.8, and more preferably satisfies the relationship 0<a+b+c+d≦0.4.

The sulfide desirably satisfies the relationships 0≤a≤0.8, 0≤b≤0.2, 0≤c≤0.2, and 0≤d≤0.6. The sulfide more desirably satisfies the relationships 0≤a≤0.5, 0≤b≤0.1, 0≤c≤0.1, and 0<d≤0.4.

In the sulfide, the transition metal element that replaces at least one of copper, tin, and typical metal elements other than tin is desirably selected from the group consisting of Mn, Fe, Co, Ni, Cu, and Zn. At least one. In the sulfide, when the transition metal element is Cu, Cu replaces tin or a typical metal element other than tin.

The sulfide desirably has a crystal structure with predominantly tetrahedrally arranged anions. Structures in which anions are arranged in a tetrahedral pattern include, for example, crystal structures such as a zincblende structure, a wurtzite structure, and an inverse fluorite structure. The sulfide more desirably has a crystal structure of at least one of a sphalerite structure and a wurtzite structure, and more desirably a sphalerite structure. The zincblende crystal structure is a structure in which a cubic close-packed lattice of anions is expanded, and half of the tetrahedral voids composed of anions are occupied by cations. Therefore, in the zincblende crystal structure, even if the cation sites are replaced by elements of different sizes, the remaining half of the voids not occupied by cations buffer the distortion of the structure. For this reason, it is believed that a certain proportion or less of elements can replace cations in the zincblende crystal structure. In addition, the zincblende structure tends to have higher electrical conductivity than sulfide having a thiospinel-type crystal structure composed of the same elements, and has advantageous properties as a thermoelectric conversion material. Structures similar to the zinc blende type include structures such as a colucite 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 configuration.

The above sulfide can be produced, for example, by sintering a powder obtained by mixing powder of copper, powder of tin, powder of a typical metal element other than tin, and powder of a transition metal element. When the transition metal element is Cu, the sulfide can be produced by sintering powder obtained by mixing powder of copper, powder of tin, and powder of typical metal elements other than tin. For mixing these powders, for example, a known device such as a ball mill can be used. Moreover, the method of sintering the powder is, for example, spark plasma sintering or hot pressing. The sintering temperature is, for example, 150°C to 1500°C, preferably 200°C to 1000°C. The sintering time is, for example, 0 to 10 minutes, preferably 0 to 5 minutes. Moreover, the temperature rising time required from the start of the sintering process to reaching the maximum temperature during the sintering process is, for example, 2 to 10 minutes. For example, the temperature inside the die filled with powder is raised to the maximum temperature in the above heating time, the temperature inside the die is maintained at the maximum temperature for a predetermined time (sintering time), and then heating is stopped. to allow the sintered body to cool naturally. The pressure to press the powder during the sintering process is, for example, 0.5 MPa to 100 MPa, preferably 5 MPa to 50 MPa. If the size of the pellet is large or if it is necessary to increase the mechanical strength of the pellet, it is preferable to further lengthen the sintering time or heating 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, nanometer-order sulfide particles (for example, having a particle size of 100 nm or less) synthesized by the liquid-phase reduction method efficiently scatter phonons by adjusting the particle size, resulting in a low lattice It is expected to exhibit thermal conductivity.

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

An example of the hydrothermal synthesis method will be described. A copper compound, a tin compound, a typical metal element other than tin, and a sulfur compound or elemental sulfur are added to water so that the substance amount ratio of the target material is achieved, and if necessary, another transition metal compound. are also added and mixed to prepare a mixture. Next, hydrothermal synthesis is performed by placing the mixed liquid in an environment of temperature of 150 to 300° C. and pressure of 0.5 to 9 MPa (megapascal) for a predetermined period. The copper compound in this production method is, for example, chlorides such _{as CuCl and CuCl2, copper nitrates such as Cu(NO3)2 , or} copper acetates such as Cu( _CH3COO ) and Cu( _CH3COO ) ₂ . be. Tin compounds in this process are, 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. As for typical metal elements other than tin, compounds such as chlorides, nitrates, and acetates can be used as supply sources of the metal elements. Alternative transition metal sources can be compounds such as chlorides, nitrates, and acetates.

An example of the liquid phase reduction method will be described. First, a copper compound, a tin compound, and a typical metal element other than tin are added to an organic solvent so that the contents of copper, tin, and typical metal elements other than tin in the total amount of metals contained in the sulfide fall within the above ranges. A mixture solution containing a metal element compound, a transition metal compound substituting at least one of copper, tin, and typical metal elements other than tin, and a sulfur compound and/or elemental sulfur is prepared. Preparation of the mixed solution is performed, for example, in an environment of normal temperature and normal pressure. Next, the mixed liquid is placed in an environment filled with an inert gas at a temperature of 150 to 350° C. for a predetermined period of time to synthesize a thermoelectric conversion material.

In this method, the compound of the metal can be, for example, a chloride, a nitrate compound, a carboxylic acid, or a complex compound such as a metal acetylacetonate. In this method, the sulfur compound is, for example, (i) a thiol such as octanethiol, decanethiol, and dodecanethiol, (ii) a 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 a thiol. In this case, the liquid organic sulfur compound can serve as an organic solvent in the mixture. The liquid mixture may contain a liquid organic compound other than the liquid organic sulfur compound. Such liquid organic compounds include, for example, (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 Polyhydric alcohols such as tetraethylene glycol may be mentioned.

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

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

<Thermoelectric conversion material>
This sulfide has advantageous properties for thermoelectric conversion materials. Therefore, the thermoelectric conversion material according to the present invention contains the above sulfides. The thermoelectric conversion material may be composed only of this sulfide, or may further contain other components together with this sulfide. It should be noted that this sulfide may be used in 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 above sulfide. In this case, the thermoelectric conversion element includes the 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, a plurality of second thermoelectric conversion materials 20 alternately arranged with the first thermoelectric conversion materials 10, and adjacent first thermoelectric conversion materials 10 A conductor 30 connecting the thermoelectric conversion material 10 and the second thermoelectric conversion material 20 is provided. For example, multiple first thermoelectric conversion materials 10 and multiple second thermoelectric conversion materials 20 are connected in series by conductors 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 thermoelectric conversion elements. As shown in FIG. 1A, the conductors 30 are disposed on, for example, a given substrate 40a or 40b. Each of the substrate 40a and the substrate 40b is, for example, a ceramic substrate having high thermal conductivity.

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

The present invention will be described in more detail below using examples. In addition, the following examples are examples of the present invention, and the present invention is not limited to the following examples.

<Example 1>
1.154 g of copper powder, 0.098 g of aluminum powder, 0.7762 g of tin powder, 0.040 g of manganese powder, and 0.932 g of sulfur powder were placed in a planetary ball mill manufactured by Retsch and milled at 400 rpm (revolutions per minute). ) for 9 minutes and then stopped for 1 minute were repeated for 3 hours to obtain a mixed powder. The obtained powder was sintered with a discharge plasma sintering apparatus (manufactured by Sinterland, model number: LABOX-125). The sintering is performed by filling a 10 mm diameter die with 0.75 g of powder, increasing the temperature inside the die to 800°C at a rate of 100°C/min, and then raising the temperature inside the die to 800°C for 2 It was done by keeping for a minute. After that, both sides of the pellet, which is a sintered product taken out from the die, were polished with abrasive paper having a particle size of #2000 based on JIS R 6001:1998, and a sample according to Example 1 was obtained. The composition of _{the sample} according to _Example 1 was _{Cu5AlMn0.2Sn1.8S8} .

<Example 2>
Instead of the above powders, 1.154 g of copper powder, 0.098 g of aluminum powder, 0.776 g of tin powder, 0.041 g of iron powder, and 0.932 g of sulfur powder were used to obtain a mixed powder. A sample according to Example 2 was obtained in the same manner as in Example 1 except for the above. _The composition of the _sample according to _Example 2 was _{Cu5AlFe0.2Sn1.8S8} .

<Example 3>
Instead of the above powders, 1.153 g of copper powder, 0.098 g of aluminum powder, 0.775 g of tin powder, 0.043 g of cobalt powder, and 0.931 g of sulfur powder were used to obtain a mixed powder. A sample according to Example 3 was obtained in the same manner as in Example 1 except for the above. The composition of _{the sample} according to _Example 3 was _{Cu5AlCo0.2Sn1.8S8} .

<Example 4>
Instead of the above powders, 1.153 g of copper powder, 0.098 g of aluminum powder, 0.776 g of tin powder, 0.043 g of nickel powder, and 0.931 g of sulfur powder were used to obtain a mixed powder. A sample according to Example 4 was obtained in the same manner as in Example 1 except for the above. The composition of _{the sample} according to _{Example 4} was Cu5AlNi0.2Sn1.8S8 .

<Example 5>
Example 1 except that a mixed powder was obtained by using 1.198 g of copper powder, 0.098 g of aluminum powder, 0.775 g of tin powder, and 0.930 g of sulfur powder instead of the above powders. A sample according to Example 5 was obtained in the same manner as above. _{The composition of} the sample according to Example 5 was Cu5.2AlSn1.8S8 .

<Example 6>
Instead of the above powders, 1.151 g of copper powder, 0.098 g of aluminum powder, 0.774 g of tin powder, 0.047 g of zinc powder, and 0.930 g of sulfur powder were used to obtain a mixed powder. A sample according to Example 6 was obtained in the same manner as in Example 1 except for the above. _The composition of _{the sample} according to Example 6 was _{Cu5AlZn0.2Sn1.8S8} .

<Example 7>
Instead of the above powders, 1.042 g of copper powder, 0.377 g of indium powder, 0.701 g of tin powder, 0.039 g of nickel powder, and 0.842 g of sulfur powder were used to obtain a mixed powder. A sample according to Example 7 was obtained in the same manner as in Example 1, except that the sintering temperature was changed to 600°C. _The composition of _the sample according to _Example 7 was _{Cu5InNi0.2Sn1.8S8} .

<Example 8>
1.093 g of copper powder, 0.046 g of aluminum powder, 0.198 g of indium powder, 0.735 g of tin powder, 0.045 g of zinc powder, and 0.883 g of sulfur powder were substituted for the above powders. A sample according to Example 8 was obtained in the same manner as in Example 1, except that a mixed powder was obtained using _The composition of _the sample _according to _Example 8 was _{Cu5Al0.5In0.5Zn0.2Sn1.8S8 .}

<Example 9>
20 mmol of copper neodecanoate, 4 mmol of indium 2-ethylhexanoate, 6.4 mmol of tin 2-ethylhexanoate, 1.6 mmol of nickel 2-ethylhexanoate, 100 ml of dodecanethiol, and 100 ml of oleylamine are mixed and stirred to uniformly disperse. A mixed liquid was obtained. Next, a container containing the mixed liquid was placed in a space filled with argon gas, and the mixed liquid was heated to 260° C. and stirred for 3 hours to obtain a liquid in which particles were precipitated. Methanol was added to the liquid thus obtained, and the mixture was centrifuged at 5000 rpm for 5 minutes to collect the precipitate. The collected precipitate was washed with hexane and methanol. After that, the resulting precipitate was dispersed in 50 ml of toluene, this dispersion was mixed with a solution of 2.5 g of thiourea dissolved in methanol, and the mixture was subjected to ultrasonic treatment to remove the surface treatment agent. replaced. After that, the solid matter was washed with hexane, methanol, and toluene, and further vacuum-dried using a vacuum dryer. Thus, the powder according to Example 9 was obtained. The powder according to Example 9 was sintered and polished in the same manner as in Example 1 except that the sintering temperature was set to 600° C. to obtain a sample according to Example 9.

<Reference example>
Example 1 except that a mixed powder was obtained by using 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 instead of the above powders. A sample of Reference Example was obtained in the same manner as above. _The composition of _the sample according to the reference example was _Cu5AlSn2S8 .

<Measurement of electrical conductivity and Seebeck coefficient>
Using a thermoelectric property evaluation device (manufactured by Ozawa Scientific Co., Ltd., product name: RZ2001i) or a thermoelectric property evaluation device (manufactured by ULVAC-RIKO, product name: ZEM-3), the electrical conductivity σ of the samples according to Examples 1 to 9 was measured. The results are shown in Figures 2A-2E. The electric resistivity ρ was obtained by taking the reciprocal of the electric conductivity σ of the samples according to Examples 1 to 9. The results are shown in Figures 2A-2I. The Seebeck coefficient S of the samples according to Examples 1 to 9 was measured using the thermoelectric property evaluation apparatus described above. The results are shown in Figures 3A-3I. In the samples according to Examples 1 to 9, the power factor PF was obtained from the Seebeck coefficient S and the electric conductivity σ based on the above formula (2). The results are shown in Figures 3A-3I.

The power factor PF was obtained in the same manner as in Examples 1 to 9 for the samples according to Reference Example. FIG. 4 shows the representative value of the power factor PF of each example shown in FIGS. 3A to 3I and the power factor of the sample according to the reference example.

<X-ray diffraction measurement>
Using an X-ray diffractometer (manufactured by Rigaku, product name: MiniFlex600), X-ray diffraction patterns of the samples according to Examples 1 to 9 were obtained. CuKα rays were used as X-rays. The X-ray diffraction patterns of the samples according to Examples 1-9 are shown in FIGS. 5A-5I.

Claims (3)

It has a composition represented by Cu5 _{- aAlxbIn1 -xcSn2 -} dDa _{+b+c+ dS8} , where D is a transition metal element, and 0≤x≤1 and 0< satisfying the relationship a + b + c + d ≤ 0.4,
The transition metal element is at least one selected from the group consisting of Mn, Fe, Co, Ni, Cu, and Zn,
1.2 ×10 ⁻⁴ Wm ⁻¹ K ⁻² or more at 350 K to 650 K, 1.4×10 ⁻⁴ W m ⁻¹ K ⁻² or more at 380 K to 390 K, and 1.7× at 470 K to 490 K. having a power factor of 10 ⁻⁴ Wm ⁻¹ K ⁻² or more and 1.8×10 ⁻⁴ Wm ⁻¹ K ⁻² or more at 570 K to 580 K ;
sulfide. A thermoelectric conversion material containing the sulfide according to claim 1 . A thermoelectric conversion element comprising the thermoelectric conversion material according to claim 2 .

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