JP7640223B2 - Thermoelectric conversion materials, thermoelectric conversion elements, and sulfides - Google Patents

Description

Applicable to Article 30, Paragraph 2 of the Patent Act. Published as a proceedings of the 99th Spring Annual Meeting of the Chemical Society of Japan. Date of publication: March 1, 2019, URL: https://nenkai.csj.jp/Proceeding/?year=2019

Applicable to Article 30, Paragraph 2 of the Patent Act. Presented at the 99th Spring Annual Meeting of the Chemical Society of Japan (held at Konan University Okamoto Campus), presentation date: March 16, 2019.

Article 30, paragraph 2 of the Patent Act applied. Published as a proceedings of the 38th International Thermoelectric Conference and the 4th Asian Thermoelectric Conference. Date of publication: June 29, 2019, Address: http://ict2019. kr/pages. php? p=2_4_1_1

Patent Law Article 30, Paragraph 2 applied. Presented at the 38th International Thermoelectric Conference and the 4th Asian Thermoelectric Conference (held at Hwabaek International Convention Center, Korea) Presentation date: July 2, 2019

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

In recent years, sulfides have been attracting particular attention as semiconductor materials such as thermoelectric conversion materials and solar cell materials. Solar cell materials are materials that absorb light such as ultraviolet light, visible light, or infrared light, and convert light energy into electrical energy by the photovoltaic effect. Materials containing silicon or gallium arsenide have been put to practical use as solar cell materials. Meanwhile, in recent years, research on the application of sulfide materials such as copper-indium-selenium sulfide (CIS) or copper-zinc-tin sulfide (CZTS) to solar cell materials has also been active. In addition, Non-Patent Documents 1 and 2 describe methods for synthesizing nanoparticles of Cu ₃ AlSnS ₅ and Cu ₃ InSnS ₅ , respectively, and the authors have considered the application to solar cells and measured the ultraviolet-visible-near infrared absorption spectra and current-voltage curves of these materials.

A thermoelectric conversion material is a material that generates a voltage due to a temperature difference between both ends of a material by the Seebeck effect, converts thermal energy into electrical energy, or generates a temperature difference by electrical energy by the Peltier effect. In recent years, sulfides containing copper and other metals have been attracting attention as thermoelectric conversion materials. For example, Non-Patent Documents 3 and 4 report the thermoelectric properties of Cu ₂₆ V ₂ M ₆ S ₃₂ (M=Ge, Sn) having a corrucite structure and Cu ₂₆ V ₂ M ₆ S ₃₂ having a corrucite structure, respectively. In addition, Patent Document 1 describes a thermoelectric conversion material 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 a main component. In addition, in Non-Patent Document 5, the thermoelectric properties of Cu ₅ AlSn ₂ S ₈ , which has a base structure of Cu ₂ SnS ₃ and in which part of Cu or Sn is replaced by Al, are predicted by first-principles calculations.

Non-Patent Document 6 describes that the thermal conductivity of Cu ₂ Tl ₂ SnS ₄ is 0.6 W/(m·K) at 300K.

JP 2016-48730 A

ChemPlusChem, (Germany), 2015, Vol.80, 652-655 CrystEngComm,(Eng), 2013, Vol.15, p.10459-10463 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

Patent Document 1 and Non-Patent Documents 3 to 6 do not disclose a specific thermoelectric conversion material containing a sulfide having Cu, Sn, and at least one of Al, Zn, and In. In addition, Non-Patent Documents 1 and 2 do not disclose any measurement results regarding the thermoelectric properties of Cu ₃ AlSnS ₅ and Cu ₃ InSnS ₅ .

In light of these circumstances, the present invention provides a thermoelectric conversion material containing a sulfide of a specific composition having Cu, Sn, and at least one of Al, Zn, and In. The present invention also provides a thermoelectric conversion material containing a sulfide of a specific composition having Cu, Sn, and at least one of Al, Zn, In, and Ga. The present invention also provides a novel sulfide that can be used for thermoelectric conversion and energy conversion such as solar cells.

The present invention relates to
Cu _ha M _ib Sn _jc D _a+b+c S _k ,
M is at least one element selected from Al, In, and Zn;
D is a metal element other than Cu, Al, In, Zn, and Sn;
a ≧ 0, b ≧ 0, c ≧ 0, 2.8 ≦ h ≦ 3.2, 0.8 ≦ i ≦ 1.2, and 0.8 ≦ j ≦ 1.2 are satisfied, and k is a value that maintains electrical neutrality;
When M contains Zn, 0≦a+b+c≦0.2;
When M does not contain Zn, it contains sulfides, where 0≦a+b+c≦0.5;
A thermoelectric conversion material is provided.

The present invention also provides a method for producing a method for manufacturing a semiconductor device comprising the steps of:
Cu _ha Al _x-b1 In _ix-b2 Sn _jc Z _a+b1+b2+c S _k ,
Z is a metal element other than Cu, Al, In, and Sn;
Contains a sulfide that satisfies 0≦x≦i, a≧0, b1≧0, b2≧0, c≧0, 0≦a+b1+b2+c≦0.5, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2, and k is a value that maintains electrical neutrality;
A thermoelectric conversion material is provided.

The present invention also provides a method for producing a method for manufacturing a semiconductor device comprising the steps of:
Cu _ha Al _x-b3 Zn _ix-b4 Sn _jc T _a+b3+b4+c S _k ,
T is a metal element other than Cu, Al, Zn, and Sn;
Contains a sulfide that satisfies 0≦x≦i, a≧0, b3≧0, b4≧0, c≧0, 0≦a+b3+b4+c≦0.2, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2, and k is a value that maintains electrical neutrality;
A thermoelectric conversion material is provided.

The present invention also provides a method for producing a method for manufacturing a semiconductor device comprising the steps of:
Cu _ha R _ib Sn _jc E _a+b+c S _k ,
R is at least one element selected from Al, In, Zn, and Ga;
E is a metal element other than Cu, Al, In, Zn, Ga, and Sn;
a ≧ 0, b ≧ 0, c ≧ 0, 2.8 ≦ h ≦ 3.2, 0.8 ≦ i ≦ 1.2, and 0.8 ≦ j ≦ 1.2 are satisfied, and k is a value that maintains electrical neutrality;
When R contains Zn, 0≦a+b+c≦0.2;
If R does not contain Zn, then 0≦a+b+c≦0.5, and it contains sulfides.
A thermoelectric conversion material is provided.

The present invention also provides a method for producing a method for manufacturing a semiconductor device comprising the steps of:
Cu _ha Al _x-b1 Ga _ix-b2 Sn _jc J _a+b1+b2+c S _k ,
J is a metal element other than Cu, Al, Ga, and Sn;
Contains a sulfide that satisfies 0≦x≦i, a≧0, b1≧0, b2≧0, c≧0, 0≦a+b1+b2+c≦0.5, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2, and k is a value that maintains electrical neutrality;
A thermoelectric conversion material is provided.

The present invention also provides a method for producing a method for manufacturing a semiconductor device comprising the steps of:
A thermoelectric conversion element including the above thermoelectric conversion material is provided.

The present invention also provides a method for producing a method for manufacturing a semiconductor device comprising the steps of:
Cu _ha M _ib Sn _jc D _a+b+c S _k ,
M is at least one element selected from Al, In, and Zn, and contains Zn;
D is a metal element other than Cu, Al, In, Zn, and Sn;
a≧0, b≧0, c≧0, 0≦a+b+c≦0.2, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2 are satisfied, and k is a value that maintains electrical neutrality,
Provide sulfides.

The present invention also provides a method for producing a method for manufacturing a semiconductor device comprising the steps of:
Cu _ha Al _x-b1 In _ix-b2 Sn _jc Z _a+b1+b2+c S _k ,
Z is a metal element other than Cu, Al, In, and Sn;
Provided is a sulfide that satisfies 0≦x≦i, a≧0, b1≧0, b2≧0, c≧0, 0≦a+b1+b2+c≦0.5, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2, and k is a value that maintains electrical neutrality.

The present invention also provides a method for producing a method for manufacturing a semiconductor device comprising the steps of:
Cu _ha Al _x-b3 Zn _ix-b4 Sn _jc T _a+b3+b4+c S _k ,
T is a metal element other than Cu, Al, Zn, and Sn;
Provided is a sulfide that satisfies 0≦x≦i, a≧0, b3≧0, b4≧0, c≧0, 0≦a+b3+b4+c≦0.2, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2, and k is a value that maintains electrical neutrality.

The present invention also provides a method for producing a method for manufacturing a semiconductor device comprising the steps of:
Cu _ha R _ib Sn _jc E _a+b+c S _k ,
R is at least one element selected from Al, In, Zn, and Ga, and contains Ga;
E is a metal element other than Cu, Al, In, Zn, Ga, and Sn;
a ≧ 0, b ≧ 0, c ≧ 0, 2.8 ≦ h ≦ 3.2, 0.8 ≦ i ≦ 1.2, and 0.8 ≦ j ≦ 1.2 are satisfied, and k is a value that maintains electrical neutrality;
When R contains Zn, 0≦a+b+c≦0.2;
When R does not contain Zn, 0≦a+b+c≦0.5.
Provide sulfides.

The present invention also provides a method for producing a method for manufacturing a semiconductor device comprising the steps of:
Cu _ha Al _x-b1 Ga _ix-b2 Sn _jc J _a+b1+b2+c S _k ,
J is a metal element other than Cu, Al, Ga, and Sn;
Provided is a sulfide that satisfies 0≦x≦i, a≧0, b1≧0, b2≧0, c≧0, 0≦a+b1+b2+c≦0.5, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2, and k is a value that maintains electrical neutrality.

The above thermoelectric conversion material contains a sulfide having Cu, Sn, and at least one of Al, Zn, and In, or contains a sulfide having Cu, Sn, and at least one of Al, Zn, In, and Ga, and has desired thermoelectric properties. In addition, the above sulfide can be used as a material for energy conversion such as a thermoelectric conversion material.

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 a thermoelectric conversion element according to the present invention. FIG. 2A is a graph showing the X-ray diffraction pattern of the powder of Example 1. FIG. 2B is a graph showing the X-ray diffraction pattern of the powder of Example 2. FIG. 2C is a graph showing the X-ray diffraction pattern of the powder of Example 3. FIG. 2D is a graph showing the X-ray diffraction pattern of the powder of Example 4. FIG. 2E is a graph showing the X-ray diffraction pattern of the powder of Example 5. FIG. 2F is a graph showing the X-ray diffraction pattern of the powder of Example 6. FIG. 2G is a graph showing the X-ray diffraction pattern of the powder of Example 7. FIG. 2H is a graph showing the X-ray diffraction pattern of the powder of Example 8. FIG. 2I is a graph showing the X-ray diffraction pattern of the powder of Example 9. FIG. 2J is a graph showing the X-ray diffraction pattern of the powder of Example 10. FIG. 3A is a graph showing an X-ray diffraction pattern of the sample according to Example 1. FIG. 3B is a graph showing the X-ray diffraction pattern of the sample according to Example 2. FIG. 3C is a graph showing the X-ray diffraction pattern of the sample according to Example 3. FIG. 3D is a graph showing the X-ray diffraction pattern of the sample according to Example 4. FIG. 3E is a graph showing the X-ray diffraction pattern of the sample according to Example 5. FIG. 3F is a graph showing the X-ray diffraction pattern of the sample according to Example 6. FIG. 3G is a graph showing the X-ray diffraction pattern of the sample according to Example 7. FIG. 3H is a graph showing the X-ray diffraction pattern of the sample according to Example 8. FIG. 4A is a graph showing the temperature change in thermal conductivity of the sample according to Example 1. FIG. 4B is a graph showing the temperature change in thermal conductivity of the sample according to Example 2. FIG. 4C is a graph showing the temperature change in thermal conductivity of the sample according to Example 3. FIG. 4D is a graph showing the temperature change in thermal conductivity of the sample according to Example 4. FIG. 4E is a graph showing the temperature change in thermal conductivity of the sample according to Example 5. FIG. 4F is a graph showing the temperature change in thermal conductivity of the sample according to Example 6. FIG. 4G is a graph showing the change in thermal conductivity of the sample according to Example 7 with respect to temperature. FIG. 4H is a graph showing the temperature change in thermal conductivity of the sample according to Example 8. FIG. 5A is a graph showing the temperature changes in electrical conductivity and electrical resistivity of the sample according to Example 1. FIG. 5B is a graph showing the temperature changes in electrical conductivity and electrical resistivity of the sample according to Example 2. FIG. 5C is a graph showing the temperature change in electrical conductivity of the sample according to Example 3. FIG. 5D is a graph showing the temperature change in electrical conductivity of the sample according to Example 4. FIG. 5E is a graph showing the temperature change in electrical conductivity of the sample according to Example 5. FIG. 5F is a graph showing the temperature change in electrical conductivity of the sample according to Example 6. FIG. 5G is a graph showing the change in electrical conductivity with temperature of the sample according to Example 7. FIG. 5H is a graph showing the change in electrical conductivity with temperature of the sample according to Example 8. FIG. 6A is a graph showing the temperature change of the Seebeck coefficient and the power factor of the sample according to Example 1. FIG. 6B is a graph showing the temperature change of the Seebeck coefficient and the power factor of the sample according to Example 2. FIG. 6C is a graph showing the temperature change of the Seebeck coefficient and the power factor of the sample according to Example 3. FIG. 6D is a graph showing the temperature change of the Seebeck coefficient and the power factor of the sample according to Example 4. FIG. 6E is a graph showing the temperature change of the Seebeck coefficient and the power factor of the sample according to Example 5. FIG. 6F is a graph showing the temperature change of the Seebeck coefficient and the power factor of the sample according to Example 6. FIG. 6G is a graph showing the temperature change of the Seebeck coefficient and the power factor of the sample according to Example 7. FIG. 6H is a graph showing the temperature change of the Seebeck coefficient and the power factor of the sample according to Example 8. FIG. 7A is a graph showing the dimensionless figure of merit of the sample according to Example 1. FIG. 7B is a graph showing the dimensionless figure of merit of the sample according to Example 2. FIG. 7C is a graph showing the dimensionless figure of merit of the sample according to Example 3. FIG. 7D is a graph showing the dimensionless figure of merit of the sample according to Example 4. FIG. 7E is a graph showing the dimensionless figure of merit of the sample according to Example 5. FIG. 7F is a graph showing the dimensionless figure of merit of the sample according to Example 6. FIG. 7G is a graph showing the dimensionless figure of merit of the sample according to Example 7. FIG. 7H is a graph showing the dimensionless figure of merit of the sample according to Example 8. FIG. 8A is a transmission electron microscope (TEM) photograph of the powder according to Example 1. FIG. 8B is a TEM photograph of the powder according to Example 3. FIG. 8C is a TEM photograph of the powder according to Example 4. FIG. 8D is a TEM photograph of the powder according to Example 5. FIG. 8E is a TEM photograph of the powder of Example 6. FIG. 8F is a TEM photograph of the powder according to Example 7. FIG. 8G is a TEM photograph of the powder of Example 8. FIG. 8H is a TEM photograph of the powder of Example 9. FIG. 8I is a TEM photograph of the powder of Example 10.

The following describes an embodiment of the present invention. Note that the following description is an example of the present invention, and the present invention is not limited to this.

<Thermoelectric conversion materials>
The thermoelectric conversion material according to the present invention contains a sulfide having a composition represented by Cu _ha M _ib Sn _jc D _a+b+c S _k . Here, M is at least one element selected from Al, In, and Zn. D is a metal element other than Cu, Al, In, Zn, and Sn. D may be one type of element or multiple types of elements. The sulfide satisfies a ≧ 0, b ≧ 0, c ≧ 0, 2.8 ≦ h ≦ 3.2, 0.8 ≦ i ≦ 1.2, and 0.8 ≦ j ≦ 1.2. In addition, k is a value that maintains the electrical neutrality of the sulfide. k is, for example, 5. Furthermore, when M contains Zn, 0 ≦ a + b + c ≦ 0.2, and when M does not contain Zn, 0 ≦ a + b + c ≦ 0.5. As a result of extensive trial and error, the present inventors have newly discovered that a material containing a sulfide having such a composition exhibits desired thermoelectric properties.

In the sulfide, M may contain only one element selected from Al, In, and Zn, or may contain two or more elements selected from Al, In, and Zn.

M includes, for example, Zn. In this case, the band gap of the thermoelectric conversion material is narrowed, and it is expected that the thermoelectric conversion material will exhibit high thermoelectric performance in the low temperature range. In addition, it is believed that by adjusting the amount of Zn, the electron density at the edge of the valence band increases, making it easier to increase the Seebeck coefficient of the thermoelectric conversion material.

In the sulfide, D is, for example, at least one selected from the group consisting of Mn, Fe, Co, and Ni. D may also be Ga.

The sulfide may have a composition represented by Cu _ha Al _x-b1 In _ix-b2 Sn _jc A _a+b1+b2+c S _k . Here, A is a metal element other than Cu, Al, In, and Sn. A may be one type of element or multiple types of elements. The sulfide satisfies 0≦x≦i, a≧0, b1≧0, b2≧0, c≧0, 0≦a+b1+b2+c≦0.5, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2. In addition, k is a value that maintains the electrical neutrality of the sulfide. k is, for example, 5.

A is, for example, at least one element selected from the group consisting of Mn, Fe, Co, Ni, and Zn. A may also be Ga.

The sulfide may have a composition represented by Cu _ha Al _x-b3 Zn _ix-b4 Sn _jc Q _a+b3+b4+c S _k . Q is a metal element other than Cu, Al, Zn, and Sn. 0≦x≦i, a≧0, b3≧0, b4≧0, c≧0, 0≦a+b3+b4+c≦0.2, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2 are satisfied. k is a value that maintains electrical neutrality. k is, for example, 5.

Q is, for example, at least one element selected from the group consisting of Mn, Fe, Co, and Ni. Q may be Ga.

The sulfide typically satisfies h+i+j=5.0. The sulfide satisfies, for example, h=3.0, i=1.0, and j ₌ 1.0. The sulfide desirably has a composition represented by _{Cu3AlxIn1 -xSnS5 .} Here, 0≦x≦1 is satisfied. The sulfide may have a composition represented _{by Cu3AlSnS5} or may have a composition represented by _Cu3InSnS5 . The sulfide desirably may have a composition represented by _{Cu3AlxZn1 -xSnS5 . Here} , 0≦x≦ ₁ is satisfied. In this case, the sulfide may have a composition represented _{by Cu3ZnSnS5} .

From another viewpoint, the thermoelectric conversion material according to the present invention may be a material containing a sulfide having a composition represented by Cu _ha Al _x-b1 In _ix-b2 Sn _jc Z _a+b1+b2+c S _k . Z is a metal element other than Cu, Al, In, and Sn. Z may be one type of element or multiple types of elements. The sulfide satisfies 0≦x≦i, a≧0, b1≧0, b2≧0, c≧0, 0≦a+b1+b2+c≦0.5, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2. In addition, k is a value that maintains the electrical neutrality of the sulfide. k is, for example, 5. As a result of extensive trial and error, the present inventors have newly discovered that such a material also exhibits the desired thermoelectric properties.

Z is, for example, at least one element selected from the group consisting of Mn, Fe, Co, Ni, Zn, and Ga. This sulfide typically satisfies h+i+j=5.0. This sulfide typically satisfies h=3.0, i=1.0, and j=1.0.

From another viewpoint, the thermoelectric conversion material according to the present invention may be a material containing a sulfide having a composition represented by Cu _ha Al _x-b3 Zn _ix-b4 Sn _jc T _a+b3+b4+c S _k . T is a metal element other than Cu, Al, Zn, and Sn. T may be one type of element or multiple types of elements. The sulfide satisfies 0≦x≦i, a≧0, b3≧0, b4≧0, c≧0, 0≦a+b3+b4+c≦0.2, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2. In addition, k is a value that maintains the electrical neutrality of the sulfide. k is, for example, 5. As a result of extensive trial and error, the present inventors have newly discovered that such a material also exhibits the desired thermoelectric properties.

T is, for example, at least one element selected from the group consisting of Mn, Fe, Co, Ni, and Ga. This sulfide typically satisfies h+i+j=5.0. This sulfide typically satisfies h=3.0, i=1.0, and j=1.0.

From another viewpoint, the thermoelectric conversion material according to the present invention may be a material containing a sulfide having a composition represented by Cu _ha R _ib Sn _jc E _a+b+c S _k . R is at least one element selected from Al, In, Zn, and Ga. E is a metal element other than Cu, Al, In, Zn, Ga, and Sn. E may be one type of element or multiple types of elements. The sulfide satisfies a ≧ 0, b ≧ 0, c ≧ 0, 2.8 ≦ h ≦ 3.2, 0.8 ≦ i ≦ 1.2, and 0.8 ≦ j ≦ 1.2. In addition, k is a value that maintains the electrical neutrality of the sulfide. k is, for example, 5. Furthermore, when R contains Zn, 0 ≦ a + b + c ≦ 0.2, and when R does not contain Zn, 0 ≦ a + b + c ≦ 0.5. The present inventors, after much trial and error, have newly discovered that such materials also exhibit the desired thermoelectric properties.

E is, for example, at least one element selected from the group consisting of Mn, Fe, Co, and Ni.

From another viewpoint, the thermoelectric conversion material according to the present invention may be a material containing a sulfide having a composition represented by Cu _ha Al _x-b1 Ga _ix-b2 Sn _jc J _a+b1+b2+c S _k . J is a metal element other than Cu, Al, Ga, and Sn. J may be one type of element or multiple types of elements. The sulfide satisfies 0≦x≦i, a≧0, b1≧0, b2≧0, c≧0, 0≦a+b1+b2+c≦0.5, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2. In addition, k is a value that maintains the electrical neutrality of the sulfide. k is, for example, 5. As a result of extensive trial and error, the inventors have newly discovered that such a material also exhibits the desired thermoelectric properties.

J is, for example, at least one element selected from the group consisting of Mn, Fe, Co, Ni, and Zn.

The sulfide having a composition represented by Cu _ha R _ib Sn _jc E _a+b+c S _k and the sulfide having a composition represented by Cu _ha Al _x-b1 Ga _ix-b2 Sn _jc J _a+b1+b2+c S _k typically satisfy h+i+j=5.0. The sulfide, for example, satisfies h=3.0, i=1.0, and j=1.0. The sulfide desirably has a composition represented by Cu ₃ Al _x Ga _1-x SnS _5. Here, 0≦x≦1 is satisfied. The sulfide may have a composition represented by Cu ₃ GaSnS ₅ .

The sulfide preferably has a crystal structure in which anions are mainly arranged tetrahedronally. Examples of the structure in which anions are arranged tetrahedronally include a zinc blende structure, a wurtzite structure, and an inverse fluorite structure. More preferably, the sulfide has at least one crystal structure of a zinc blende structure and a wurtzite structure. The zinc blende crystal structure is a structure in which a cubic close-packed lattice of anions is expanded, and half of the vacancies of the tetrahedrons consisting of anions are occupied by cations. Therefore, even if the cation sites are replaced by elements of different sizes in the zinc blende crystal structure, the remaining half of the vacancies not occupied by cations buffers the distortion of the structure. For this reason, it is considered that elements of a certain ratio or less can replace cations in the zinc blende crystal structure. In addition, the zinc blende structure is more likely to have a high electrical conductivity than sulfides having a thiospinel crystal structure composed of the same elements, and has advantageous properties as a thermoelectric conversion material. Examples of structures similar to zinc blende include the corrucite structure, germanite structure, stannite structure, and kesterite structure. These structures also have anions arranged in a tetrahedral shape.

In the thermoelectric conversion material, the sulfide is, for example, sintered. This makes it easier for the sulfide to have the desired properties as a thermoelectric conversion material. In addition, the thermoelectric conversion material can be molded into a predetermined shape, making it easier to handle the thermoelectric conversion material in the manufacture of thermoelectric conversion elements.

The thermoelectric conversion material has, for example, a lattice thermal conductivity of 1.3 W/(m·K) or less at 373 to 673 K.

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

On the other hand, the thermal conductivity κ is expressed as 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 formula (3), which is known as the Wiedemann-Franz law. Here, L is the Lorentz number, which can be treated as a constant for metal materials, but it is known that it is smaller than the constant used for metal materials in semiconductor materials, and according to Applied Physics Letters, (US), 2015, Vol.3, 041506, it is proposed to define L as shown in formula (4). S in formula (4) is the Seebeck coefficient.
κ = κcar + κlat (2)
κcar=LσT (3)
L=1.5+exp(-│S│/116) (4)

As such, when the carrier thermal conductivity κcar is low, the electrical conductivity σ also tends to be low, and a low carrier thermal conductivity κcar is not necessarily advantageous from the perspective 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 perspective of increasing the dimensionless figure of merit ZT.

The following sulfides may be used for applications other than thermoelectric conversion materials. The sulfides have a composition represented by Cu _ha M _ib Sn _jc D _a+b+c S _k . Here, M is at least one element selected from Al, In, and Zn, and contains Zn. In addition, D is a metal element other than Cu, Al, In, Zn, and Sn. This sulfide satisfies a ≧ 0, b ≧ 0, c ≧ 0, 0 ≦ a + b + c ≦ 0.2, 2.8 ≦ h ≦ 3.2, 0.8 ≦ i ≦ 1.2, and 0.8 ≦ j ≦ 1.2. In addition, k is a value that maintains the electrical neutrality of the sulfide.

In this sulfide, D is, for example, at least one selected from the group consisting of Mn, Fe, Co, and Ni. D may also be Ga.

This sulfide can be used, for example, as a material for energy conversion. For example, this sulfide can potentially be used as a material for solar cells. In this case, the sulfide may be in the form of particles, a film, or fibers. By including Zn, the band gap of the sulfide tends to become narrower. In addition, the ionic radius of Zn is close to that of Cu, and they are easily substituted, so that when used as a material for solar cells, etc., the properties of the material can be easily adjusted.

The following sulfides may be used for applications other than thermoelectric conversion materials. The sulfides have a composition represented by Cu _ha Al _x-b1 In _ix-b2 Sn _jc Z _a+b1+b2+c S _k . Z is a metal element other than Cu, Al, In, and Sn. The sulfides satisfy 0≦x≦i, a≧0, b1≧0, b2≧0, c≧0, 0≦a+b1+b2+c≦0.5, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2. In addition, k is a value that maintains the electrical neutrality of the sulfide.

In this sulfide, Z is, for example, at least one element selected from the group consisting of Mn, Fe, Co, Ni, Zn, and Ga.

The following sulfide may be used for applications other than thermoelectric conversion materials. The sulfide has a composition represented by Cu _ha Al _x-b3 Zn _ix-b4 Sn _jc T _a+b3+b4+c S _k . T is a metal element other than Cu, Al, Zn, and Sn. The sulfide satisfies 0≦x≦i, a≧0, b3≧0, b4≧0, c≧0, 0≦a+b3+b4+c≦0.2, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2. In addition, k is a value that maintains the electrical neutrality of the sulfide.

In this sulfide, T is, for example, at least one element selected from the group consisting of Mn, Fe, Co, Ni, and Ga.

The following sulfides may be used for applications other than thermoelectric conversion materials. The sulfides have a composition represented by Cu _ha R _ib Sn _jc E _a+b+c S _k . Here, R is at least one element selected from Al, In, Zn, and Ga, and includes Ga. In addition, E is a metal element other than Cu, Al, In, Zn, Ga, and Sn. The sulfides satisfy a ≧ 0, b ≧ 0, c ≧ 0, 0 ≦ a + b + c ≦ 0.2, 2.8 ≦ h ≦ 3.2, 0.8 ≦ i ≦ 1.2, and 0.8 ≦ j ≦ 1.2. In addition, k is a value that maintains the electrical neutrality of the sulfide.

E is, for example, at least one element selected from the group consisting of Mn, Fe, Co, and Ni.

The following sulfides may be used for applications other than thermoelectric conversion materials. The sulfides have a composition represented by Cu _ha Al _x-b1 Ga _ix-b2 Sn _jc J _a+b1+b2+c S _k . Here, J is a metal element other than Cu, Al, Ga, and Sn. The sulfides satisfy 0≦x≦i, a≧0, b1≧0, b2≧0, c≧0, 0≦a+b1+b2+c≦0.5, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2. Furthermore, k is a value that maintains the electrical neutrality of the sulfide.

J is, for example, at least one element selected from the group consisting of Mn, Fe, Co, Ni, and Zn.

The above sulfides contained in the thermoelectric conversion material and the above sulfides usable for applications other than thermoelectric conversion materials can be synthesized, for example, by a liquid-phase reduction method. Sulfide particles of nanometer order (e.g., having a particle diameter of 100 nm or less) synthesized by the liquid-phase reduction method are expected to efficiently scatter phonons and exhibit low lattice thermal conductivity by adjusting the particle diameter. The sulfide particles have an average particle diameter of, for example, 100 nm or less. The sulfide particles preferably have an average particle diameter of 50 nm or less. The average particle diameter of the sulfide particles can be determined, for example, as follows. Ten or more sulfide particles are observed by TEM to determine the particle diameter of each particle. At this time, a rectangle with the minimum area circumscribing the TEM image of each particle is drawn, and the lengths of the long side and short side of the drawn rectangle are defined as the long axis and short axis of the particle, respectively, and the particle diameter of each particle is determined from the relationship of particle diameter = (long axis of particle + short axis of particle) / 2. The arithmetic mean of the particle sizes of each particle is then determined as the average particle size of the sulfide particles.

An example of the liquid phase reduction method is described below. A mixed liquid containing a copper compound, a tin compound, at least one of an aluminum compound, a zinc compound, an indium compound, and a gallium compound, and a sulfur compound and/or elemental sulfur is prepared in a specific organic solvent. The mixed liquid is prepared, for example, in an environment at room temperature and 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 specific period of time to synthesize a thermoelectric conversion material.

In this method, the copper compound is, for example, (i) a chloride such as CuCl and _CuCl2 , (ii) a copper nitrate such as Cu( _NO3 ) ₂ , (iii) a copper carboxylate such as Cu( _CH3COO ), Cu( _CH3COO ) ₂ , and copper neodecanoate, or (iv) a complex compound such as copper acetylacetonate soluble in an organic solvent. In this method, the tin compound is, for example, a chloride such as _SnCl2 and _SnCl4 , a tin nitrate, a tin carboxylate, or a complex compound such as tin acetylacetonate. In this method, the aluminum compound, zinc compound, indium compound, and gallium compound are, for example, chlorides of aluminum, zinc, indium, and gallium, nitrates of aluminum, zinc, indium, and gallium, carboxylates of aluminum, zinc, indium, and gallium, or complex compounds such as acetylacetonate of aluminum, zinc, indium, and gallium. 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) an organic sulfur compound such as thioacetamide. The organic sulfur compound is preferably a liquid organic sulfur compound such as thiol. In this case, the liquid organic sulfur compound can play the role of an organic solvent in the mixed liquid. The mixed liquid may contain a liquid organic compound other than the liquid organic sulfur compound. Examples of such liquid organic compounds include, for example, (i) an amine such as oleylamine, (ii) an unsaturated fatty acid such as myristoleic acid, palmitoleic acid, and oleic acid, or (iii) a polyhydric alcohol such as ethylene glycol, triethylene glycol, and tetraethylene glycol.

The inert gas used in this method is not particularly limited as long as it is inert to the mixed liquid, but may be, for example, a rare gas such as argon or nitrogen. The pressure in the environment in which the mixed liquid is placed is preferably normal pressure.

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

According to this method, the synthesized sulfide precipitates. The precipitated sulfide is separated by a solid-liquid separation method such as centrifugation using a specified organic solvent, and is washed with a specified organic solvent as necessary and dried. In this way, a thermoelectric conversion material containing sulfide can be obtained.

The thermoelectric conversion material thus obtained may be in powder form. The thermoelectric conversion material may be produced by further sintering the powder containing sulfide. The method for sintering the powder containing sulfide is not particularly limited, but may be, 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. The heating time required from the start of the sintering process to reach the maximum temperature during the sintering process is, for example, 2 to 10 minutes. For example, the temperature inside the die filled with the powder is raised to the maximum temperature in the above heating time, the temperature inside the die is kept at the maximum temperature for a predetermined time (sintering time), and then heating is stopped to allow the sintered body to cool naturally. In sintering by spark plasma sintering, the pressure to pressurize the powder during the sintering process is, for example, 0.5 MPa to 100 MPa, and preferably 5 MPa to 50 MPa. On the other hand, in sintering by hot pressing, the pressure to pressurize the powder during the sintering process is, for example, 5 MPa to 500 MPa, and preferably 200 MPa to 400 MPa. When the pellet size is large or when the mechanical strength of the pellet needs to be increased, it is preferable to further extend the sintering time or the temperature rise time in order to obtain a uniform sintered body. This sintering process can be performed in an inert gas atmosphere or a vacuum atmosphere. This sintering process is preferably performed in a vacuum atmosphere.

Each of the above sulfides contained in the thermoelectric conversion material and the above sulfides usable for applications other than thermoelectric conversion materials may be produced by, for example, sintering a powder obtained by mixing copper powder, tin powder, and at least one of aluminum powder, zinc powder, indium powder, and gallium powder. For mixing these powders, a known device such as a ball mill can be used. The method for sintering the powder is, for example, spark plasma sintering or hot pressing. In this case, the conditions for the spark plasma sintering or hot pressing described above regarding the spark plasma sintering or hot pressing of the powder containing the sulfide obtained by the liquid phase reduction method can be applied as the conditions for the spark plasma sintering or hot pressing.

Each of the above sulfides contained in the thermoelectric conversion material and the above sulfides usable for applications other than thermoelectric conversion materials may be synthesized by a melting method or a hydrothermal synthesis method.

The melting method is a method of reacting raw materials at high temperatures to obtain the desired compound. One example of the melting method is to vacuum seal the raw materials in a quartz tube or the like so that the mass ratio of the desired materials is achieved, and then react the raw materials at a predetermined reaction temperature using a heating device such as an electric furnace.

An example of the hydrothermal synthesis method will be described. A mixture is prepared by adding and mixing at least one of a copper compound, a tin compound, an aluminum compound, a zinc compound, an indium compound, and a gallium compound, and a sulfur compound or elemental sulfur in water so as to obtain a substance amount ratio of the target material. Next, the mixture is placed in an environment of a temperature of 150 to 300°C and a pressure of 0.5 to 9 MPa (megapascals) for a predetermined period of time to perform hydrothermal synthesis. The copper compound in this manufacturing method is, for example, a chloride such as CuCl and CuCl ₂ , a copper nitrate such as Cu(NO ₃ ) ₂ , or a copper carboxylate such as Cu(CH ₃ COO) and Cu(CH ₃ COO) _2. The tin compound in this manufacturing method is, for example, a chloride such as SnCl ₂ and SnCl ₄ , a tin nitrate, or a tin carboxylate. The aluminum compound, zinc compound, indium compound, and gallium compound in this manufacturing method are, for example, aluminum chloride, zinc chloride, indium chloride, and gallium chloride, aluminum nitrate, zinc nitrate, indium nitrate, and gallium nitrate, or aluminum carboxylate, zinc carboxylate, indium carboxylate, and gallium carboxylate. The sulfur compound in this manufacturing method is, for example, an organic sulfur compound such as thiourea and thioacetamide.

<Thermoelectric conversion element>
The above-mentioned sulfide-containing thermoelectric conversion material for thermoelectric conversion materials can be used to fabricate a thermoelectric conversion element. In this case, the thermoelectric conversion element includes the above-mentioned sulfide-containing thermoelectric conversion material.

For example, the thermoelectric conversion element includes a thermoelectric conversion material containing the above-mentioned 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 arranged alternately with the first thermoelectric conversion materials 10, and a conductor 30 connecting adjacent first thermoelectric conversion materials 10 and second thermoelectric conversion materials 20. For example, the plurality of first thermoelectric conversion materials 10 and the plurality of second thermoelectric conversion materials 20 are connected in series by the conductor 30. The first thermoelectric conversion material 10 is a thermoelectric conversion material containing the above-mentioned sulfide. On the other hand, the second thermoelectric conversion material 20 is a known n-type semiconductor that can be used in a thermoelectric conversion element. As shown in FIG. 1A, the conductor 30 is arranged on, for example, a predetermined substrate 40a or substrate 40b. Each of the substrates 40a and 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 a conductor 60 that connects adjacent first thermoelectric conversion materials 50 to each other. 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 that contains the above-mentioned sulfide. As shown in FIG. 1B, the conductor 60 is disposed, for example, on a predetermined 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. Note that the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

Example 1
3 millimoles (mmol) of copper acetate, 1 mmol of aluminum acetylacetone, 1 mmol of tin acetate, 100 ml of dodecanethiol, and 100 ml of oleylamine were mixed and stirred to obtain a uniformly dispersed mixed solution A. Next, a container containing mixed solution A was placed in a space filled with argon gas, and mixed solution A was heated to 260° C. and stirred for 1 hour 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, and the solid containing the precipitate was vacuum-dried using a vacuum dryer. In this way, the powder according to Example 1 was obtained.

The powder according to Example 1 was sintered using a spark plasma sintering device (manufactured by Sinterland, model number: LABOX-125). This sintering was carried out by filling a die with 0.75 g of the powder according to Example 1, raising the temperature inside the die to 450°C at a rate of 100°C/min, and then maintaining the temperature inside the die at 450°C for 2 minutes. After that, both sides of the pellet, which was the sintered product removed from inside the die, were polished using polishing paper with a grain size of #2000 based on Japanese Industrial Standards (JIS) R 6001:1998 to obtain a sample according to Example 1.

Example 2
18 mmol of copper neodecanoate, 6 mmol of indium 2-ethylhexanoate, 6 mmol of tin 2-ethylhexanoate, 100 ml of dodecanethiol, and 100 ml of oleylamine were mixed and stirred to obtain a uniformly dispersed mixed liquid B. Next, a container containing mixed liquid B was placed in a space filled with nitrogen gas, and mixed liquid B was heated to 240° 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, and the solid containing the precipitate was vacuum-dried using a vacuum dryer. In this way, a powder according to Example 2 was obtained. The powder according to Example 2 was sintered and polished in the same manner as the powder according to Example 1 to obtain a sample according to Example 2.

Example 3
5 mmol of copper acetate, 0.75 mmol of aluminum acetylacetone, 0.25 mmol of zinc acetylacetone, 2 mmol of tin acetate, 100 ml of dodecanethiol, and 100 ml of oleylamine were mixed and stirred to obtain a uniformly dispersed mixed solution C. The mixed solution C thus obtained was subjected to the powder preparation, sintering, and polishing treatment in the same manner as in Example 1 to obtain a sample according to Example 3.

Example 4
5 mmol of copper acetate, 0.5 mmol of aluminum acetylacetone, 0.5 mmol of zinc acetylacetone, 2 mmol of tin acetate, 100 ml of dodecanethiol, and 100 ml of oleylamine were mixed and stirred to obtain a uniformly dispersed mixture D. The mixture D thus obtained was subjected to the same powder preparation, sintering, and polishing treatments as in Example 1 to obtain a sample according to Example 4.

Example 5
5 mmol of copper acetate, 0.25 mmol of aluminum acetylacetone, 0.75 mmol of zinc acetylacetone, 2 mmol of tin acetate, 100 ml of dodecanethiol, and 100 ml of oleylamine were mixed and stirred to obtain a uniformly dispersed mixture E. The mixture E thus obtained was subjected to the same powder preparation, sintering, and polishing treatment as in Example 1 to obtain a sample according to Example 5.

Example 6
5 mmol of copper acetate, 1 mmol of zinc acetylacetone, 2 mmol of tin acetate, 100 ml of dodecanethiol, and 100 ml of oleylamine were mixed and stirred to obtain a uniformly dispersed mixture F. The mixture F thus obtained was subjected to the powder recovery, sintering, and polishing processes in the same manner as in Example 1 to obtain a sample according to Example 6.

Example 7
5 mmol of copper acetate, 0.75 mmol of aluminum acetylacetone, 0.5 mmol of gallium acetylacetone, 2 mmol of tin acetate, 100 ml of dodecanethiol, and 100 ml of oleylamine were mixed and stirred to obtain a uniformly dispersed mixed solution G. Next, a container containing the mixed solution G was placed in a space filled with argon gas, and the mixed solution G was heated to 260° C. and stirred for 1 hour to obtain a liquid in which particles were precipitated. The liquid thus obtained was centrifuged at 5000 rpm for 5 minutes to recover the precipitate. The recovered precipitate was washed with hexane, and the solid containing the precipitate was vacuum-dried using a vacuum dryer. In this way, the powder according to Example 7 was obtained. The powder according to Example 7 was sintered and polished in the same manner as the powder according to Example 1 to obtain a sample according to Example 7.

Example 8
5 mmol of copper acetate, 0.5 mmol of aluminum acetylacetone, 1 mmol of gallium acetylacetone, 2 mmol of tin acetate, 100 ml of dodecanethiol, and 100 ml of oleylamine were mixed and stirred to obtain a uniformly dispersed mixture H. The mixture H thus obtained was subjected to the powder recovery, sintering, and polishing treatment in the same manner as in Example 7 to obtain a sample according to Example 8.

<Example 9>
5 mmol of copper acetate, 0.25 mmol of aluminum acetylacetone, 1.5 mmol of gallium acetylacetone, 2 mmol of tin acetate, 100 ml of dodecanethiol, and 100 ml of oleylamine were mixed and stirred to obtain a uniformly dispersed mixture I. The mixture I thus obtained was subjected to the powder recovery, sintering, and polishing treatment in the same manner as in Example 7 to obtain a sample according to Example 9.

Example 10
5 mmol of copper acetate, 2 mmol of acetylacetone gallium, 2 mmol of tin acetate, 100 ml of dodecanethiol, and 100 ml of oleylamine were mixed and stirred to obtain a uniformly dispersed mixture J. The mixture J thus obtained was subjected to the powder recovery, sintering, and polishing processes in the same manner as in Example 7 to obtain a sample according to Example 10.

<X-ray diffraction measurement>
Using an X-ray diffractometer (manufactured by Rigaku Corporation, product name: MiniFlex600), X-ray diffraction patterns were obtained for each powder before sintering by spark plasma sintering in Examples 1 and 2. CuKα rays were used as X-rays. X-ray diffraction patterns for each powder in Examples 1 to 6 are shown in Figures 2A to 2F. From these results, it was suggested that the powder before sintering by spark plasma sintering in Example 1 has a wurtzite crystal structure. It was also suggested that the powder before sintering by spark plasma sintering in Example 2 has a wurtzite crystal structure and a composition of _{Cu3InSnS5 .} It was suggested _that the powders before sintering by spark plasma sintering in _{Examples 3} to ₁₀ had a crystal structure of _{a wurtzite type structure and} had compositions _{of Cu3Al0.75Zn0.25SnS5 , Cu3Al0.5Zn0.5SnS5 , Cu3Al0.25Zn0.75SnS5 , Cu3ZnSnS5 , Cu3Al0.75Ga0.25SnS5 , Cu3Al0.5Ga0.5SnS5 , Cu3Al0.25Ga0.75SnS5 , and Cu3GaSnS5 , respectively} .

Using an energy dispersive X-ray analyzer (EDS) (Hitachi High-Technologies Corporation, product name: TM3030), EDS was performed on the samples made from the powders before sintering by spark plasma sintering in Examples 1 and 3 to 10, and on the samples made from each sample after sintering by spark plasma sintering in Examples 1 and 3 to 6, and the abundance ratios of Cu, Al, Zn, Ga, and Sn based on atomic number were measured. The results are shown in Table 1.

Using an X-ray diffractometer (Rigaku Corporation, product name: MiniFlex600) or a fully automated multipurpose X-ray diffractometer (Rigaku Corporation, product name: SmartLab), the X-ray diffraction patterns of each sample after sintering by spark plasma sintering in Examples 1 to 8 were obtained. CuKα rays were used as the X-rays. The X-ray diffraction patterns of each sample after sintering by spark plasma sintering in Examples 1 to 8 are shown in Figures 3A to 3H. These results suggest that each sample after sintering by spark plasma sintering in Examples 1 to 8 has at least one of a wurtzite crystal structure and a zinc blende crystal structure.

<Measurement of thermal conductivity>
The thermal conductivity of each sample according to Examples 1 to 8 was measured at a plurality of temperatures in the range of 300 to 700 K. The thermal conductivity was measured using a laser flash method thermal property measuring device (manufactured by Netzsch, product name: Lfa457) or a laser flash method thermal property measuring device (manufactured by Kyoto Electronics Manufacturing Co., Ltd., product name: LFA-502). The results are shown in Figures 4A to 4H.

<Measurement of Electrical Conductivity and Seebeck Coefficient>
Using a thermoelectric property evaluation device (manufactured by ULVAC-RIKO, product name: ZEM-3) or a thermoelectric property evaluation device (manufactured by Ozawa Scientific, product name: RZ2001i), the electrical conductivity σ of each sample according to Examples 1 to 8 was measured at a plurality of temperatures in the range of 300 to 700K. The results are shown in Figs. 5A to 5H. The electrical resistivity ρ was calculated by taking the reciprocal of the electrical conductivity σ of each sample according to Examples 1 and 2. The results are shown in Figs. 5A and 5B. The Seebeck coefficient S of each sample according to Examples 1 to 8 was measured using the above-mentioned thermoelectric property evaluation device. The results are shown in Figs. 6A to 6H. For each sample according to Examples 1 to 8, the power factor PF was calculated based on the Seebeck coefficient S and electrical conductivity σ according to the following formula (5). The results are shown in Figs. 6A to 6H.
PF= ^S2σ (5)

Determination of Carrier Thermal Conductivity and Lattice Thermal Conductivity
From the measurement results of the Seebeck coefficient S for each sample according to Examples 1 to 8, the Lorentz number L was determined using the above formula (4). From the measurement results of the determined Lorentz number L and the electrical conductivity σ, the carrier thermal conductivity κcar at the measurement temperature of the thermal conductivity of each sample according to Examples 1 to 8 was calculated using the above formula (3). The lattice thermal conductivity κlat at the measurement temperature of the thermal conductivity of each sample according to Examples 1 to 8 was determined by subtracting the carrier thermal conductivity κcar from the thermal conductivity according to formula (2). The results are shown in Figures 4A to 4H. As shown in Figures 4A and 4B, each sample according to Examples 1 and 2 had a lattice thermal conductivity of 1.3 W/(m·K) or less at 373 to 673 K. Each sample according to Examples 3 to 8 had a lattice thermal conductivity of 0.7 W/(m·K) or less at 373 to 673 K.

<Dimensionless performance index>
4A to 6H, the dimensionless figure of merit ZT for each sample according to the embodiment was calculated according to formula (1). The results are shown in Figures 7A to 7H.

<TEM Observation>
Samples for TEM observation were prepared from the powders before sintering according to Examples 1, 3 to 10, and TEM observation was performed. TEM photographs of the powders before sintering according to Examples 1, 3 to 10 are shown in Figures 8A to 8I. In the TEM photographs of each sample, 10 or more particles were selected, a rectangle of the smallest area circumscribing the TEM image of each particle was drawn, and the length of the long side and the length of the short side of the drawn rectangle were determined as the long axis and the short axis of the particle, respectively. The length of the long side and the short side of the drawn rectangle were determined as the long axis and the short axis of the particle, respectively, and the particle size of each particle was determined from the relationship of particle size = (particle long axis + particle short axis) / 2. The arithmetic mean of the particle size of each particle was then determined as the average particle size. The average values of the long axis and short axis of the powder in each Example and the average particle size are shown in Table 2.

Claims (9)

A sulfide having a composition represented by Cu _ha M _ib Sn _jc D _a+b+c S _k ,
M is at least one element selected from Al, In, and Zn;
D is Ga ;
a ≧ 0, b ≧ 0, c ≧ 0, 2.8 ≦ h ≦ 3.2, 0.8 ≦ i ≦ 1.2, and 0.8 ≦ j ≦ 1.2 are satisfied, and k is a value that maintains the electrical neutrality of the sulfide,
When M contains Zn, 0≦a+b+c≦0.2;
When M does not contain Zn, it contains sulfides, where 0≦a+b+c≦0.5;
The sulfide has at least one of a wurtzite crystal structure and a zinc blende crystal structure.
Thermoelectric conversion materials. The sulfide has a composition represented by Cu _ha Al _x-b1 In _ix-b2 Sn _jc A _a+b1+b2+c S _k ,
A is Ga ;
0≦x≦i, a≧0, b1≧0, b2≧0, c≧0, 0≦a + b1 + b2 + c≦0.5, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2 are satisfied, and k is a value that maintains the electrical neutrality of the sulfide.
The thermoelectric conversion material according to claim 1 . The sulfide has a composition represented by Cu _ha Al _x-b3 Zn _ix-b4 Sn _jc Q _a+b3+b4+c S _k ,
Q is Ga ;
0≦x≦i, a≧0, b3≧0, b4≧0, c≧0, 0≦a + b3 + b4 + c≦0.2, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2 are satisfied, and k is a value that maintains the electrical neutrality of the sulfide.
The thermoelectric conversion material according to claim 1 . A sulfide having a composition represented by Cu _ha Al _x-b1 In _ix-b2 Sn _jc Z _a+b1+b2+c S _k ,
Z is Zn or Ga ;
Contains a sulfide that satisfies 0≦x≦i, a≧0, b1≧0, b2≧0, c≧0, 0≦a+b1+b2+c≦0.5, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2, and k is a value that maintains the electrical neutrality of the sulfide;
The sulfide has at least one of a wurtzite crystal structure and a zinc blende crystal structure.
Thermoelectric conversion materials. A sulfide having a composition represented by Cu _ha Al _x-b3 Zn _ix-b4 Sn _jc T _a+b3+b4+c S _k ,
T is Ga ;
Contains a sulfide that satisfies 0≦x≦i, a≧0, b3≧0, b4≧0, c≧0, 0≦a+b3+b4+c≦0.2, 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2, and k is a value that maintains the electrical neutrality of the sulfide;
The sulfide has at least one of a wurtzite crystal structure and a zinc blende crystal structure.
Thermoelectric conversion materials. A sulfide having a composition represented by Cu _ha R _ib Sn _jc E _a+b+c S _k ,
R is at least one element selected from Al, In, Zn, and Ga;
E is a metal element other than Cu, Al, In, Zn, Ga, and Sn;
a ≧ 0, b ≧ 0, c ≧ 0, 2.8 ≦ h ≦ 3.2, 0.8 ≦ i ≦ 1.2, and 0.8 ≦ j ≦ 1.2 are satisfied, and k is a value that maintains the electrical neutrality of the sulfide,
Contains sulfides , where a+b+c=0;
The sulfide has at least one of a wurtzite crystal structure and a zinc blende crystal structure.
Thermoelectric conversion materials. A sulfide having a composition represented by Cu _ha Al _x-b1 Ga _ix-b2 Sn _jc J _a+b1+b2+c S _k ,
J is a metal element other than Cu, Al, Ga, and Sn;
Contains a sulfide that satisfies 0≦x≦i, a≧0, b1≧0, b2≧0, c≧0, a+b1+b2+c=0 , 2.8≦h≦3.2, 0.8≦i≦1.2, and 0.8≦j≦1.2, and k is a value that maintains the electrical neutrality of the sulfide;
The sulfide has at least one of a wurtzite crystal structure and a zinc blende crystal structure.
Thermoelectric conversion materials. The thermoelectric conversion material according to any one of claims 1 to 7, wherein the sulfide is sintered. A thermoelectric conversion element comprising the thermoelectric conversion material according to any one of claims 1 to 8.

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