JP6718800B2 - Sulfide, semiconductor material, and thermoelectric conversion material - Google Patents

Description

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

In recent years, sulfides have attracted attention as semiconductor materials, especially as thermoelectric conversion materials. The thermoelectric conversion material is a material that causes voltage to be generated by the temperature difference between both ends of the material by the Seebeck effect to convert thermal energy into electric energy, or causes temperature difference by 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 the movement of electrons from a higher thermal energy to a lower thermal energy and a p-type thermoelectric conversion material in which a current is generated by the movement of holes. As a thermoelectric conversion material, an alloy thermoelectric conversion material, a silicide thermoelectric conversion material, a tellurium thermoelectric conversion material, and an oxide thermoelectric conversion material are known.

In recent years, a sulfide that has been attracting attention as a thermoelectric conversion material is a sulfide containing copper and other metals. For example, in Non-Patent Documents 1 to 3, Cu ₂₆ V ₂ M ₆ S ₃₂ (M=Ge, Sn) having a corusite structure and Cu _26-X Zn _X V ₂ M ₆ S having a corusite structure, respectively. ₃₂ , and the thermoelectric properties of Cu _12-x Ni _x Sb ₄ S ₁₃ tetrahedrite have been reported. Further, Patent Document 1 is made of 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 a p-block element, as main components. , Thermoelectric conversion materials are described.

On the other hand, 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 the photovoltaic effect. As a solar cell material, a material using silicon or gallium arsenide has been put into practical use, but in recent years, it relates to a material such as copper-indium-selenium sulfide (CIS) or copper-zinc-tin sulfide (CZTS). Research is active.

JP, 2016-48730, A

Applied Physics Letters, (US), 2014, Vol. 105, 132107 Journal of Applied Physics, (US), 2014, Vol. 116, 063706 Journal of Applied Physics, (US), 2013, Vol. 113, 043712

According to the description of Patent Document 1, there is room for devising another novel sulfide having advantageous properties as a thermoelectric conversion material. The materials described in Non-Patent Documents 1 to 3 need to include a metal having toxicity such as vanadium (V) or antimony (Sb).

Currently, 60% or more of the energy used is discarded as heat, and 70% or more of the discarded heat is said to be low-temperature waste heat. Therefore, from an economical point of view, a thermoelectric conversion material having high thermoelectric properties in a medium to low temperature range (for example, room temperature to 400°C) is desired. The tellurium-based thermoelectric conversion material has high thermoelectric properties in the medium to low temperature range. However, since tellurium simple substance and tellurium compound have high toxicity and tellurium is a rare element, tellurium-based thermoelectric conversion materials are difficult to be widely used for general applications.

Therefore, the present invention provides a novel sulfide that is advantageous in exhibiting high thermoelectric properties in the medium to low temperature range without containing vanadium, antimony, and tellurium.

The present invention is
In the X-ray diffraction pattern obtained using CuKα rays, 2θ=16.35°±0.1°, 2θ=18.32°±0.1°, and 2θ=20.05°±0.1° A sulfide having a diffraction peak of, and a crystal structure containing copper, tin and/or germanium, and a Group 6 metal element is provided.

The present invention is
Provided is a sulfide having a crystal structure containing copper, tin and/or germanium, and a Group 6 metal element.

The present invention is
Provided is a semiconductor material containing the above sulfide.

The present invention is
Provided is a thermoelectric conversion material containing the above sulfide.

The above-mentioned sulfide has advantageous properties as a thermoelectric conversion material in the medium to low temperature range even if it does not contain vanadium, antimony, and tellurium.

The graph which shows the X-ray-diffraction pattern of the sulfide which concerns on Example 1. A graph showing a simulation result of an X-ray diffraction pattern of a sulfide having a composition of Cu ₁₃ MoSn ₃ S _16.

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

The sulfide according to the present invention is 2θ=16.35°±0.1°, 2θ=18.32°±0.1°, and 2θ=20 in the X-ray diffraction pattern obtained using CuKα radiation. It is a sulfide that has a diffraction peak of 0.05°±0.1° and has a crystal structure containing copper, tin and/or germanium, and a Group 6 metal element. This sulfide has advantageous properties as a thermoelectric conversion material in the temperature range of medium to low temperature, even if it does not contain vanadium, antimony, and tellurium. The X-ray diffraction pattern obtained using the CuKα ray of the sulfide according to the present invention may have diffraction peaks other than the above.

From another point of view, the sulfide according to the present invention has a colusite type crystal structure containing copper, tin and/or germanium, and a Group 6 metal element. This sulfide has advantageous properties as a thermoelectric conversion material in the temperature range of medium to low temperature, even if it does not contain vanadium, antimony, and tellurium. The crystal structure of sulfide can be determined, for example, by obtaining an X-ray diffraction pattern of sulfide. In this case, for example, CuKα rays are used as the X-rays. For example, in the X-ray diffraction pattern obtained by using CuKα rays, the corusite-type crystal structure has 2θ=16.35°±0.1°, 2θ=18.32°±0.1°, and 2θ. =20.05°±0.1°.

The Group 6 metal element contained in the crystal structure of sulfide desirably contains at least one of molybdenum and tungsten. As a result, the sulfide is likely to have advantageous properties as a thermoelectric conversion material in the medium to low temperature range.

The Group 6 metal element contained in the crystal structure of sulfide more preferably contains molybdenum. As a result, the sulfide is more likely to have advantageous characteristics as a thermoelectric conversion material in the medium to low temperature range.

The sulfide crystal structure desirably does not include lead, antimony, selenium, tellurium, and vanadium. This makes it possible to produce a sulfide without using a simple substance of lead, antimony, selenium, tellurium, and vanadium or a compound containing these elements, and thus it is easy to produce a sulfide safely. Moreover, since sulfides can be produced without using toxic substances, environmental pollution due to materials can be prevented.

The above sulfide can be used as a semiconductor material or a thermoelectric conversion material. Therefore, the semiconductor material of the present invention contains the above sulfide. Further, the thermoelectric conversion material of the present invention contains the above sulfide.

In some cases, the above-mentioned sulfide can be used as a semiconductor material other than the thermoelectric conversion material and also as a material for a photovoltaic cell such as a solar cell.

The dimensionless figure of merit ZT and the power factor PF are known as indexes showing the performance of thermoelectric conversion materials. Here, Z means a figure of merit and has a dimension of K ^-1 . Further, T means absolute temperature. The larger the dimensionless figure of merit ZT, the higher the performance of the thermoelectric conversion material. The dimensionless figure of merit ZT and the power factor PF of the thermoelectric conversion material are defined by the following equations (1) and (2), respectively. α, σ, and κ mean the Seebeck coefficient, electrical conductivity, and thermal conductivity of the thermoelectric conversion material, respectively.
ZT=α ² σT/κ (1)
PF=α ² σ (2)

The thermoelectric conversion material has a dimensionless figure of merit ZT of more than 0.05 at 40 to 50°C, for example. As described above, the thermoelectric conversion material containing the above-mentioned sulfide can exhibit high thermoelectric characteristics in the medium to low temperature range.

The crystal structure of sulfide may include an element other than copper, tin and/or germanium, a Group 6 metal element, and sulfur. For example, the number of atoms of elements other than copper, tin and/or germanium, Group 6 metal elements, and sulfur which may be included in the crystal structure of sulfide includes all atoms included in the crystal structure of sulfide. It is 10% or less of the number of atoms of the element. The crystal structure of the sulfide desirably contains only copper, tin and/or germanium, a Group 6 metal element, and sulfur.

Next, an example of the method for producing a sulfide according to the present invention will be described. The method for producing a sulfide of the present invention includes a mixing step of mixing raw materials containing copper, tin and/or germanium, a Group 6 metal element, and sulfur, and a sintering step of sintering the mixture obtained by the mixing step. And In the mixing step, sulfur, copper, tin and/or germanium, and a simple substance or a compound as a raw material of the Group 6 metal element are mixed in a predetermined mass ratio. The shape and size of the raw material are not particularly limited, and may be a lump having a certain size, or a granule or a powder. The method of mixing the raw materials is not particularly limited, and for example, a method of pulverizing and mixing using a planetary ball mill, a bead mill, a powder mixer, or the like can be considered. This allows the raw materials to be crushed and uniformly mixed. As a method of mixing the raw materials, a known method known as dry mixing or wet mixing can be used in addition to the method of pulverizing and mixing.

Further, the sulfide according to the present invention may be synthesized in solution. For example, a composite metal sulfide can be synthesized by adding a sulfiding agent to an aqueous solution of a metal salt such as a metal nitrate, a metal chloride, or a metal acetate or an aqueous solution of a metal complex such as a metal acetylacetonate. In this case, examples of the sulfiding agent include sulfides of alkali metals such as sodium sulfide and potassium sulfide, sulfides of alkaline earth metals, sulfides of ammonium ions such as ammonium sulfide, and thiourea or thioacetamide. Compounds such as sulfur organic compounds may be mentioned. Further, the sulfide can also be obtained by blowing hydrogen sulfide gas into an aqueous solution in which metal ions are dissolved under an appropriate hydrogen ion concentration to generate a precipitate of a composite metal sulfide.

The sulfide according to the present invention may be synthesized in an organic solvent. In this case, the particle size of the primary particles of sulfide can be reduced to several nanomail. For example, in an amine solvent such as triethylenetetramine or octylamine, or in a thiol solvent such as octanethiol or decanethiol, a metal salt such as metal nitrate, metal chloride, or metal carboxylate or metal acetylacetate. A sulfide can be obtained by mixing a metal complex such as nato and a sulfur-containing organic compound such as thiourea, thioacetamide, or dithiocarbamic acid or a sulfur powder in a predetermined amount and refluxing the mixture.

The sulfide according to the present invention may be synthesized by hydrothermal synthesis. In this case, a copper compound, a compound of tin and/or germanium, a compound of a Group 6 metal element, and a sulfur compound or elemental sulfur are added to water and mixed to prepare a mixed solution. Hydrothermal synthesis is performed by leaving the mixed solution in an environment of a predetermined temperature and a predetermined pressure for a predetermined period. Thereby, sulfide can be synthesized. The copper compound used in this method includes, for example, chlorides such as CuCl and CuCl _2, copper nitrate such as Cu(NO ₃ ) ₂ or carvone such as Cu(CH ₃ COO) and Cu(CH ₃ COO) _2. It is acid copper. The tin or germanium compound used in this method is, for example, a chloride such as SnCl ₂ , SnCl ₄ , GeCl ₂ , or GeCl ₄ , a nitric acid compound of tin or germanium, or a carboxylic acid compound of tin or germanium. The compound of the Group 6 metal element used in this method is, for example, a chloride, a nitric acid compound, or a carboxylic acid compound of the Group 6 metal element. The sulfur compounds used in this method are, for example, organic sulfur compounds such as thiourea and thioacetamide. The mixed liquid is prepared, for example, in an environment of normal temperature (20° C.±15° C.: Japanese Industrial Standard JIS Z 8703) and normal pressure.

The temperature of the environment in which the hydrothermal synthesis is performed in the above method is, for example, 120 to 300°C, preferably 150 to 250°C. The pressure of this environment is, for example, 0.1 to 5 MPa (megapascal) in gauge pressure, and preferably 0.2 to 3 MPa.

The sulfide obtained in the aqueous solution or in the organic solvent is separated from the aqueous solution or the organic solvent by a solid-liquid separation method such as filtration or centrifugation. In this case, since molecules of impurities derived from the aqueous solution, the organic solvent, or the raw material are attached to the surface of the sulfide particles, it is necessary to perform washing or calcination before the sintering step described below. It is preferable to remove impurities from the sulfide particles by the method described above. For example, the sulfide obtained in an aqueous solution or in an organic solvent can be subjected to a sintering step described below to produce a sulfide sintered body.

In the sintering step, the mixture obtained by mixing the raw materials or the synthesized sulfide is filled in a mold having a predetermined shape and sintered while being pressurized. As a method of sintering the mixture or the synthesized sulfide while pressurizing in this manner, for example, spark plasma sintering (Spark Plasma Sintering) can be used. The sintering temperature is not particularly limited, but is, for example, 150°C to 1500°C, preferably 200°C to 1000°C. The sintering time is, for example, 0 minutes to 10 minutes, and preferably 0 minutes to 5 minutes. In addition, 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 minutes to 10 minutes. For example, the temperature inside the mold filled with the mixture or the synthesized sulfide is raised to the maximum temperature at the above-mentioned heating rate, and the temperature inside the mold is kept at the maximum temperature for a predetermined time (sintering time). After that, the heating is stopped and the sintered body is naturally cooled. Thus, by shortening the sintering time, it becomes possible to perform sintering while maintaining the primary particle size. Thereby, the thermal conductivity can be lowered and the figure of merit can be improved. The pressure for pressurizing the mixture or the synthesized sulfide during the sintering step is, for example, 0.5 MPa to 100 MPa, preferably 5 MPa to 50 MPa. This sintering process can be performed in an inert gas atmosphere or a vacuum atmosphere. This sintering step is preferably performed in a vacuum atmosphere. In this way, a sulfide sintered body can be obtained. In this way, a material having high mechanical strength can be manufactured by sintering the mixture of raw materials or the synthesized sulfide while pressurizing.

The present invention will be described in detail below 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>
1.38 g of copper powder, 0.60 g of tin powder, 0.16 g of molybdenum powder, and 0.86 g of sulfur powder were charged into a Lecce planetary ball mill, and the planetary ball mill was rotated at 300 rpm (rotations per minute) for 9 minutes, and then for 1 minute. The operation of stopping the ball mill was repeated for 3 hours to obtain a mixed powder. The obtained mixed powder was sintered using a discharge plasma sintering device (manufactured by Sinterland Co., model number: LABOX-125). 0.75 g of the mixed powder was charged into a cylindrical die having an inner diameter of 10 mm, the temperature of the die was raised to 450° C. at 100° C./min, and the temperature of the die was raised to 500° C. at 50° C./min. The mixed powder was sintered by maintaining the die temperature at 500° C. for 2 minutes. Both sides of the pellet obtained by sintering were polished by a rotary polishing machine having a particle size of #2000 based on JIS R 6001:1998 to obtain a sample for thermoelectric conversion characteristic evaluation of Example 1 having a thickness of about 2 mm. ..

The dimensionless figure of merit (ZT) at 42.6° C. of the obtained thermoelectric conversion characteristic evaluation sample was 8.23×10 ⁻² . Here, for the thermoelectric conversion characteristic evaluation sample of Example 1, the electrical resistivity at 42.6°C, 113°C, 208°C, 305°C, and 404°C was measured by the four-terminal measurement method, and the electrical resistance at each temperature was measured. The electrical conductivity σ at each temperature was obtained as the reciprocal of the rate. Further, the thermal conductivity κ at room temperature (about 27° C.) of the thermoelectric conversion characteristic evaluation sample of Example 1 was measured by the laser flash method. For this measurement, a laser flash thermophysical property analyzer LFA-502 manufactured by Kyoto Electronics Manufacturing Co., Ltd. was used. Furthermore, by heating one part so that the average temperature of the thermoelectric conversion characteristic evaluation sample of Example 1 is 42.6°C, 113°C, 208°C, 305°C, and 404°C, and cooling another part, A predetermined temperature difference was generated on the upper surface of the thermoelectric conversion characteristic evaluation sample of Example 1, and the electromotive force was measured in this state. A graph showing the relationship between the temperature difference and the electromotive force in the thermoelectric conversion characteristic evaluation sample of Example 1, in which the vertical axis represents the electromotive force and the horizontal axis represents the temperature difference, was created. From the slope of this graph, the Seebeck coefficient of the thermoelectric conversion characteristic evaluation sample of Example 1 at each temperature was calculated. The dimensionless performance coefficient was calculated based on the equation (1) based on the electric conductivity, the thermal conductivity, and the Seebeck coefficient thus obtained. The power factor PF was calculated based on the equation (2) based on the electric conductivity and the Seebeck coefficient. The results are shown in Table 1.

<X-ray diffraction pattern>
An X-ray diffraction pattern of the thermoelectric conversion characteristic evaluation sample according to Example 1 was obtained using an X-ray diffractometer (Rigaku Corporation, product name: MiniFlex600). CuKα ray was used as the X-ray. The X-ray diffraction pattern of the thermoelectric conversion characteristic evaluation sample according to Example 1 is shown in FIG.

In 04-009-4458 listed in PDF-4 of International Center for Diffraction Data (ICDD), the vanadium and arsenic of Cu ₁₃ VSnAs ₂ S ₁₆ having a corusite structure are respectively contained. Substitution with molybdenum and tin was performed, and the molecular structure analysis software CASTEP from BIOVIA was used to optimize the cell constants and atomic positions while maintaining symmetry to determine a crystal structure model for simulation. RietanFP was used to simulate the X-ray diffraction pattern of the determined crystal structure model. The result is shown in FIG. The result of the XRD pattern shown in FIG. 1 almost corresponds to the simulation result shown in FIG. 2, and it was suggested that the thermoelectric conversion characteristic evaluation sample according to Example 1 had a corusite structure.

Claims (6)

In the X-ray diffraction pattern obtained using CuKα ray, 2θ=16.35°±0.1°, 2θ=18.32°±0.1°, and 2θ=20.05°±0.1° Sulfide having a crystal structure containing copper, tin and/or germanium, and a Group 6 metal element. A sulfide having a crystal structure of a colusite type, which contains copper, tin and/or germanium, and a Group 6 metal element. The sulfide according to claim 1, wherein the Group 6 metal element contains at least one of molybdenum and tungsten. A semiconductor material containing the sulfide according to claim 1. A thermoelectric conversion material comprising the sulfide according to any one of claims 1 to 3. The thermoelectric conversion material according to claim 5, which has a dimensionless figure of merit ZT greater than 0.05 at 40 to 50°C.

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