Non-stoichiometric thermoelectric material and preparation method and application thereof

Abstract

The invention relates to the technical field of thermoelectric materials, in particular to a non-stoichiometric thermoelectric material and a preparation method and application thereof. The chemical general formula of the non-stoichiometric thermoelectric material provided by the invention is Cu Fe Sn < c > S < 8-x > Se < x >, wherein 4 < = a < 7, 0 < b < = 1, 1.5 < = c < = 2, 0 < = x < = 3, and a, b, c and x are atomic ratios respectively. The thermoelectric material provided by the invention is high in density, low in resistivity and thermal conductivity and relatively high in thermoelectric performance, vacancy and doping concentration can be accurately controlled and carrier concentration and phonon scattering effect can be optimized by adjusting the ratio of the raw materials, and finally, the obtained thermoelectric material block has relatively high electrical performance and relatively low lattice thermal conductivity at the same time; and a high dimensionless thermoelectric figure of merit (ZT value) is achieved.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric materials technology, specifically to a non-stoichiometric thermoelectric material, its preparation method, and its application. Background Technology

[0002] Thermoelectric materials, as functional materials capable of directly converting heat energy into electrical energy, have attracted much attention. They can be used to manufacture thermoelectric power generation devices, effectively converting large amounts of waste heat generated during industrial production into electrical energy. Thermoelectric devices require no moving mechanical parts and do not rely on flowing substances as energy conversion media, thus offering numerous advantages: small size for portability, stable and reliable performance, pollution-free and noiseless operation, and long service life. Thermoelectric conversion technology based on thermoelectric materials provides new ideas and solutions for the sustainable use of energy and environmental protection.

[0003] Currently, many high-performance and well-developed materials are known, including Bi₂Te₃, PbTe, and Si-Ge alloys, which exhibit excellent thermoelectric properties across different temperature ranges. However, these materials face several challenges for commercial application: Bi₂Te₃ and PbTe suffer from poor machinability and contain the rare element Te and / or the toxic element Pb, while SiGe alloys are hampered by demanding preparation conditions, high energy consumption, and the high cost of Ge.

[0004] Therefore, developing thermoelectric materials with inexpensive, non-toxic, simple, easy-to-prepare, and high-performance constituent elements is of great significance to the development of thermoelectric conversion technology. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a non-stoichiometric thermoelectric material, its preparation method, and its application. This thermoelectric material exhibits high density, low resistivity and thermal conductivity, and thus high thermoelectric performance.

[0006] Therefore, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides, in an optional embodiment, a non-stoichiometric thermoelectric material, wherein the general chemical formula of the thermoelectric material is Cu. a Fe b Sn c S 8-x Se x ;

[0008] Wherein, 4≤a<7, 0<b≤1, 1.5≤c≤2, 0≤x≤3, and a, b, c and x are atomic ratios respectively.

[0009] In this invention, by adjusting the raw material ratio, the concentration of vacancies and doping can be precisely controlled, the carrier concentration and phonon scattering effect can be optimized, and the thermoelectric material bulk can be made to have both high electrical performance and low lattice thermal conductivity, thereby having a high dimensionless thermoelectric figure of merit (ZT value).

[0010] Preferably, when x is 0, then 4≤a≤6, 0.25≤b≤1, and 1.5≤c≤2.

[0011] In this invention, when x is 0, then 4≤a≤6, 0.25≤b≤1, and 1.5≤c≤2. This thermoelectric material is called a cation vacancy type thermoelectric material, and the carrier concentration and lattice thermal conductivity are controlled by Cu / Fe / Sn vacancies.

[0012] Preferably, when a is 6, then b is 1, c is 2, and 0 ≤ x ≤ 3.

[0013] In this invention, when a is 6, then b is 1, c is 2, and 0≤x≤3. This thermoelectric material is called anion-controlled thermoelectric material, which optimizes the band structure and phonon scattering by partially replacing S with Se.

[0014] Preferably, when x is 2, then 6≤a<7, 0<b≤1, c is 2, and a+b=7.

[0015] In this invention, when x is 2, then 6≤a<7, 0<b≤1, c is 2, and a+b=7. This thermoelectric material is called a cation supersaturated thermoelectric material, and its acoustic-electric transport performance is synergistically regulated by excess Cu and deficient Fe.

[0016] Preferably, the chemical formula of the thermoelectric material is Cu6FeSn2S8, Cu 5.5 FeSn2S8, Cu5FeSn2S8, Cu 4.5 FeSn2S8, Cu4FeSn2S8, Cu6Fe 0.75 Sn2S8, Cu6Fe 0.625 Sn2S8, Cu6Fe 0.5 Sn2S8, Cu6Fe 0.375 Sn2S8, Cu6Fe 0.25 Sn2S8, Cu6FeSn 1.875 S8, Cu6FeSn 1.75 S8, Cu6FeSn 1.625 S8, Cu6FeSn 1.5 S8, Cu6FeSn2S7Se1, Cu6FeSn2S6Se2, Cu6FeSn2S5Se3, Cu 6.4 Fe 0.6 Sn2S6Se2, Cu 6.7 Fe0.3 Sn2S6Se2, Cu 6.8 Fe 0.2 Sn2S6Se2 or Cu 6.9 Fe 0.1 Sn2S6Se2.

[0017] Furthermore, the chemical formula of the thermoelectric material is Cu. 6.8 Fe 0.2 Sn2S6Se2 or Cu6Fe 0.375 Sn2S8.

[0018] In this invention, when a = 6.8, the dimensionless thermoelectric figure of merit (ZT value) of the thermoelectric material at 750K can reach 0.78.

[0019] Secondly, in an optional embodiment, the present invention provides a method for preparing the above-mentioned non-stoichiometric thermoelectric material, comprising the following steps:

[0020] According to the atomic ratio of each element in the thermoelectric material, Cu elemental powder, Fe elemental powder, Sn elemental powder, S elemental powder and Se elemental powder are weighed respectively. Under a protective gas atmosphere, the raw materials are mixed and then ball-milled, sintered, and finally polished to obtain the thermoelectric material.

[0021] The ball milling time is 35-45 hours.

[0022] In this invention, atomic-level uniform mixing of elements is achieved through ball milling, and the nanocrystalline and amorphous phases formed by mechanical alloying retain grains after sintering, enhancing the phonon scattering effect while reducing element volatilization caused by high temperature.

[0023] Preferably, during the ball milling process, the mass ratio of grinding balls to raw materials is 40-50:1, and the ball milling speed is 450 rpm; the purity of the Cu elemental powder, Fe elemental powder, and Se elemental powder is ≥99.9%, and the purity of the Sn elemental powder and S elemental powder is ≥99.99%.

[0024] Preferably, the sintering method is as follows: the ball-milled powder is heated from room temperature to 500°C at a heating rate of 10°C / min, and the longitudinal pressure is increased to 15 MPa within 2 minutes; then the temperature is increased from 500°C to 650°C, and the longitudinal pressure is increased from 15 MPa to 35 MPa within 2 minutes; finally, sintering is carried out at 650°C for 1 hour; the protective gas is an argon-hydrogen mixture, in which the volume fraction of argon is 92% and the volume fraction of hydrogen is 8%.

[0025] In this invention, the ball-milled powder is heated from room temperature to 500°C at a rate of 10°C / min, and the longitudinal pressure is increased to 15MPa within 2 minutes to achieve initial densification. Heating from 500°C to 650°C and increasing the longitudinal pressure from 15MPa to 35MPa within 2 minutes, followed by sintering at 650°C for 1 hour, achieves high densification.

[0026] Thirdly, in an optional embodiment, the present invention provides the application of the above-mentioned non-stoichiometric thermoelectric material in thermoelectric power generation and refrigeration devices in the temperature range of 300-750K.

[0027] Compared with the prior art, the present invention has one of the following beneficial effects:

[0028] 1. The thermoelectric material provided by this invention has high density, low resistivity and thermal conductivity, and high thermoelectric performance. By adjusting the raw material ratio, the concentration of vacancies and doping can be precisely controlled, the carrier concentration and phonon scattering effect can be optimized, and the thermoelectric material bulk can simultaneously have high electrical performance and low lattice thermal conductivity, thereby having a high dimensionless thermoelectric figure of merit (ZT value).

[0029] 2. This invention achieves atomic-level uniform mixing of elements through ball milling, and the nanocrystals formed by mechanical alloying are retained after sintering, enhancing the phonon scattering effect while reducing element volatilization caused by high temperature.

[0030] 3. The method for preparing thermoelectric materials provided by this invention is simple to operate, consumes little energy, has a short cycle, uses low-cost raw materials, is pollution-free, and poses no high-temperature hazard. The thermoelectric material prepared in the end has good crystallinity, a dense structure, and a high reproducibility. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the process for preparing thermoelectric materials in Example 1 of the present invention;

[0033] Figure 2 The XRD diffraction patterns of the thermoelectric material prepared according to the chemical formula of Example 2 after ball milling for 10 hours, 20 hours, 40 hours and 60 hours are shown below.

[0034] Figure 3 This is a schematic diagram showing the change of total thermal conductivity as a function of temperature for the thermoelectric materials prepared in Example 1 and Comparative Examples 1-5 of the present invention;

[0035] Figure 4 This is a schematic diagram showing the change of lattice thermal conductivity as a function of temperature in the thermoelectric materials prepared in Example 1 and Comparative Examples 1-5 of the present invention.

[0036] Figure 5 This is a schematic diagram showing the power factor of the thermoelectric materials prepared in Example 1 and Comparative Examples 1-5 of the present invention as a function of temperature.

[0037] Figure 6 This is a schematic diagram showing the change of the dimensionless thermoelectric figure of merit of the thermoelectric materials prepared in Example 1 and Comparative Examples 1-5 of the present invention with temperature.

[0038] Figure 7 Differential scanning calorimetry-thermogravimetric analysis (DSC-TGA) curves of the thermoelectric material prepared in Example 2 of this invention.

[0039] Figure 8 This is a schematic diagram illustrating the density variation with temperature of the thermoelectric materials prepared in Example 2 and Comparative Examples 6-10 of the present invention.

[0040] Figure 9 The X-ray diffraction patterns of the thermoelectric materials prepared in Examples 2, 15-17 of this invention are shown below.

[0041] Figure 10 These are cross-sectional scanning electron microscope images of the thermoelectric materials prepared in Examples 16 and 17 of this invention;

[0042] Figure 11 This is a schematic diagram showing the change in resistivity of the thermoelectric materials prepared in Examples 2, 15-17 of the present invention as a function of temperature;

[0043] Figure 12 This is a schematic diagram showing the Seebeck coefficient of the thermoelectric materials prepared in Examples 2, 15-17 of the present invention as a function of temperature;

[0044] Figure 13 This is a schematic diagram showing the power factor of the thermoelectric materials prepared in Examples 2, 15-17 of the present invention as a function of temperature.

[0045] Figure 14 This is a schematic diagram showing the change in total thermal conductivity of the thermoelectric materials prepared in Examples 2, 15-17 of the present invention as a function of temperature;

[0046] Figure 15 This is a schematic diagram showing the change of the dimensionless thermoelectric figure of merit of the thermoelectric materials prepared in Examples 2, 15-17 of the present invention with temperature;

[0047] Figure 16 This is a schematic diagram showing the change in resistivity of the thermoelectric materials prepared in Examples 15 and 18-21 of the present invention as a function of temperature.

[0048] Figure 17 This is a schematic diagram showing the Seebeck coefficient of the thermoelectric materials prepared in Examples 15 and 18-21 of the present invention as a function of temperature.

[0049] Figure 18 This is a schematic diagram showing the power factor of the thermoelectric materials prepared in Examples 15 and 18-21 of the present invention as a function of temperature.

[0050] Figure 19 This is a schematic diagram showing the change of total thermal conductivity as a function of temperature for the thermoelectric materials prepared in Examples 15, 18-21 of the present invention;

[0051] Figure 20 This is a schematic diagram showing the change of lattice thermal conductivity as a function of temperature in the thermoelectric materials prepared in Examples 15, 18-21 of the present invention.

[0052] Figure 21 This is a schematic diagram showing the change of the dimensionless thermoelectric figure of merit of the thermoelectric materials prepared in Examples 15, 18-21 of the present invention with temperature.

[0053] Figure 22 The X-ray diffraction patterns of the thermoelectric materials prepared in Example 2 and Comparative Examples 11, 13, 15-17 of this invention; Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0055] In the following examples and comparative examples, Cu, Fe, Sn, S, and Se elemental powders were all produced by Zhongnuo New Materials (Beijing) Technology Co., Ltd., and the purity of Cu, Fe, and Se elemental powders was ≥99.9%, while the purity of Sn and S elemental powders was ≥99.99%.

[0056] The technical solution of the present invention will be described below with reference to the embodiments.

[0057] Example 1

[0058] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6Fe. 0.375 Sn2S8.

[0059] See Figure 1 The preparation method of the above-mentioned non-stoichiometric thermoelectric material includes the following steps:

[0060] S1: Chemical formula Cu6Fe 0.375Approximately 6 grams of raw materials were weighed out for Sn2S8 according to the stoichiometric ratio, specifically 2.5542 grams of Cu elemental powder, 0.1403 grams of Fe elemental powder, 1.5905 grams of Sn elemental powder, and 1.7149 grams of S elemental powder. The weighed raw materials were placed in a stainless steel ball mill jar (the mass ratio of stainless steel grinding balls to raw materials was 45:1). The ball mill jar was filled with an argon-hydrogen mixture as a protective gas, in which the volume fraction of hydrogen was 8% and the volume fraction of argon was 92%. The mixture was ball-milled in a planetary ball mill (MSK-SFM-1, Hefei Kejing) at a speed of 450 rpm for 40 hours to obtain a mixed powder.

[0061] S2: The prepared mixed powder is placed in a graphite mold, compacted, and then placed in a vacuum hot pressing sintering furnace. The temperature is increased from room temperature to 500°C at a rate of 10°C / min, and the longitudinal pressure is increased to 15MPa within 2 minutes. Then the temperature is increased from 500°C to 650°C, and the longitudinal pressure is increased from 15MPa to 35MPa within 2 minutes. Sintering is carried out at 650°C for 1 hour (during the sintering process, boron nitride is sprayed inside the mold for lubrication and insulation). After cooling to room temperature with the furnace, the mold is demolded and the surface is polished to obtain the thermoelectric material block.

[0062] Example 2

[0063] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn2S8.

[0064] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0065] Example 3

[0066] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu. 5.5 FeSn2S8.

[0067] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0068] Example 4

[0069] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu5FeSn2S8.

[0070] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0071] Example 5

[0072] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu. 4.5 FeSn2S8.

[0073] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0074] Example 6

[0075] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu4FeSn2S8.

[0076] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0077] Example 7

[0078] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6Fe. 0.75 Sn2S8.

[0079] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0080] Example 8

[0081] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6Fe. 0.625 Sn2S8.

[0082] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0083] Example 9

[0084] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6Fe. 0.5 Sn2S8.

[0085] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0086] Example 10

[0087] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6Fe. 0.25 Sn2S8.

[0088] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0089] Example 11

[0090] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn. 1.875 S8.

[0091] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0092] Example 12

[0093] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn. 1.75 S8.

[0094] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0095] Example 13

[0096] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn. 1.625 S8.

[0097] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0098] Example 14

[0099] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn. 1.5 S8.

[0100] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0101] Example 15

[0102] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn2S6Se2.

[0103] The preparation method of the above-mentioned non-stoichiometric thermoelectric material includes the following steps:

[0104] S1: Weigh approximately 6 grams of raw materials according to the stoichiometric ratio of Cu6FeSn2S6Se2, specifically 2.2330 grams of Cu elemental powder, 0.3270 grams of Fe elemental powder, 1.3905 grams of Sn elemental powder, 1.1245 grams of S elemental powder, and 1.1245 grams of Se elemental powder. Place the weighed raw materials into a stainless steel ball mill jar (the mass ratio of stainless steel grinding balls to raw materials is 45:1). The ball mill jar is filled with an argon-hydrogen mixture as a protective gas, wherein the volume fraction of hydrogen is 8% and the volume fraction of argon is 92%. Ball mill the mixture in a planetary ball mill (MSK-SFM-1, Hefei Kejing) at a speed of 450 rpm for 40 hours to obtain a mixed powder.

[0105] S2: The prepared mixed powder is placed in a graphite mold, compacted, and then placed in a vacuum hot pressing sintering furnace. The temperature is increased from room temperature to 500°C at a rate of 10°C / min, and the longitudinal pressure is increased to 15MPa within 2 minutes. Then the temperature is increased from 500°C to 650°C, and the longitudinal pressure is increased from 15MPa to 35MPa within 2 minutes. Sintering is carried out at 650°C for 1 hour (during the sintering process, boron nitride is sprayed inside the mold for lubrication and insulation). After cooling to room temperature with the furnace, the mold is demolded and the surface is polished to obtain the thermoelectric material block.

[0106] Example 16

[0107] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn2S7Se.

[0108] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0109] Example 17

[0110] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn2S5Se3.

[0111] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0112] Example 18

[0113] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu. 6.8 Fe 0.2 Sn2S6Se2.

[0114] The preparation method of the above-mentioned non-stoichiometric thermoelectric material includes the following steps:

[0115] S1: Chemical formula Cu6Fe 0.375 Approximately 6 grams of raw materials were weighed out for Sn2S8 according to the stoichiometric ratio, specifically: 2.5156 grams of Cu elemental powder, 0.0602 grams of Fe elemental powder, 1.3822 grams of Sn elemental powder, 1.1178 grams of S elemental powder, and 0.9193 grams of Se elemental powder. The weighed raw materials were placed in a stainless steel ball mill jar (the mass ratio of stainless steel grinding balls to raw materials was 45:1). The jar was filled with an argon-hydrogen mixture as a protective gas, with hydrogen comprising 8% by volume and argon comprising 92% by volume. The mixture was ball-milled for 40 hours at 450 rpm in a planetary ball mill (MSK-SFM-1, Hefei Kejing) to obtain the mixed powder.

[0116] S2: The prepared mixed powder is placed in a graphite mold, compacted, and then placed in a vacuum hot pressing sintering furnace. The temperature is increased from room temperature to 500°C at a rate of 10°C / min, and the longitudinal pressure is increased to 15MPa within 2 minutes. Then the temperature is increased from 500°C to 650°C, and the longitudinal pressure is increased from 15MPa to 35MPa within 2 minutes. Sintering is carried out at 650°C for 1 hour (during the sintering process, boron nitride is sprayed inside the mold for lubrication and insulation). After cooling to room temperature with the furnace, the mold is demolded and the surface is polished to obtain the thermoelectric material block.

[0117] Example 19

[0118] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu. 6.4 Fe 0.6 Sn2S6Se2.

[0119] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0120] Example 20

[0121] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu. 6.7 Fe 0.3 Sn2S6Se2.

[0122] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0123] Example 21

[0124] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu. 6.9 Fe 0.1 Sn2S6Se2.

[0125] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0126] Comparative Example 1

[0127] This comparative example provides a non-stoichiometric thermoelectric material with the chemical formula Cu6Fe. 0.375 Sn2S8.

[0128] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the ball milling time is 10 hours. This comparative example will not be repeated.

[0129] Comparative Example 2

[0130] This comparative example provides a non-stoichiometric thermoelectric material with the chemical formula Cu6Fe. 0.375 Sn2S8.

[0131] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the ball milling time is 20 hours. This comparative example will not be repeated.

[0132] Comparative Example 3

[0133] This comparative example provides a non-stoichiometric thermoelectric material with the chemical formula Cu6Fe. 0.375 Sn2S8.

[0134] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the ball milling time is 30 hours. This comparative example will not be repeated.

[0135] Comparative Example 4

[0136] This comparative example provides a non-stoichiometric thermoelectric material with the chemical formula Cu6Fe. 0.375 Sn2S8.

[0137] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the ball milling time is 50 hours. This comparative example will not be repeated.

[0138] Comparative Example 5

[0139] This comparative example provides a non-stoichiometric thermoelectric material with the chemical formula Cu6Fe. 0.375 Sn2S8.

[0140] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the ball milling time is 60 hours. This comparative example will not be repeated.

[0141] Comparative Example 6

[0142] This comparative example provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn2S8.

[0143] Except for step S2, which involves "placing the prepared mixed powder into a graphite mold, compacting it, and then placing it in a vacuum hot-pressing sintering furnace, heating it from room temperature to 450°C at a rate of 10°C / min, increasing the longitudinal pressure to 35MPa within 2 minutes, sintering at 450°C for 1 hour (during the sintering process, spraying boron nitride inside the mold for lubrication and insulation), cooling it to room temperature with the furnace, demolding and surface polishing to obtain the thermoelectric material block", the other steps are the same as in Example 1, and will not be repeated in this comparative example.

[0144] Comparative Example 7

[0145] This comparative example provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn2S8.

[0146] Except for step S2, which involves "placing the prepared mixed powder into a graphite mold, compacting it, and then placing it in a vacuum hot-pressing sintering furnace, heating it from room temperature to 500°C at a rate of 10°C / min, and increasing the longitudinal pressure to 35MPa within 2 minutes, sintering it at 500°C for 1 hour (during the sintering process, spraying boron nitride inside the mold for lubrication and insulation), cooling it to room temperature with the furnace, demolding and surface polishing to obtain the thermoelectric material block", the other steps are the same as in Example 1, and will not be repeated in this comparative example.

[0147] Comparative Example 8

[0148] This comparative example provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn2S8.

[0149] Except for step S2, which involves placing the prepared mixed powder into a graphite mold, compacting it, and then placing it into a vacuum hot-pressing sintering furnace, heating it from room temperature to 500°C at a rate of 10°C / min, and increasing the longitudinal pressure to 15MPa within 2 minutes, then heating it from 500°C to 550°C, and increasing the longitudinal pressure from 15MPa to 35MPa within 2 minutes, sintering it at 550°C for 1 hour (during the sintering process, boron nitride is sprayed inside the mold for lubrication and insulation), and after cooling to room temperature with the furnace, demolding and surface polishing are performed to obtain the thermoelectric material block, all other steps are the same as in Example 1, and will not be repeated in this comparative example.

[0150] Comparative Example 9

[0151] This comparative example provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn2S8.

[0152] Except for step S2, which involves placing the prepared mixed powder into a graphite mold, compacting it, and then placing it into a vacuum hot-pressing sintering furnace, heating it from room temperature to 500°C at a rate of 10°C / min, and increasing the longitudinal pressure to 15MPa within 2 minutes, then heating it from 500°C to 600°C, and increasing the longitudinal pressure from 15MPa to 35MPa within 2 minutes, sintering it at 600°C for 1 hour (during the sintering process, boron nitride is sprayed inside the mold for lubrication and insulation), and after cooling to room temperature with the furnace, demolding and surface polishing are performed to obtain the thermoelectric material block, all other steps are the same as in Example 1, and will not be repeated in this comparative example.

[0153] Comparative Example 10

[0154] This comparative example provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn2S8.

[0155] Except for step S2, which involves "placing the prepared mixed powder into a graphite mold, compacting it, and then placing it in a vacuum hot-pressing sintering furnace, heating it from room temperature to 500°C at a rate of 10°C / min, and increasing the longitudinal pressure to 15MPa within 2 minutes, then heating it from 500°C to 700°C, and increasing the longitudinal pressure from 15MPa to 35MPa within 2 minutes, sintering it at 700°C for 1 hour (during the sintering process, boron nitride is sprayed inside the mold for lubrication and insulation), and after cooling to room temperature with the furnace, demolding and surface polishing are performed to obtain the thermoelectric material block," all other steps are the same as in Example 1, and will not be repeated in this comparative example.

[0156] Comparative Example 11

[0157] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu. 3.5 FeSn2S8.

[0158] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0159] Comparative Example 12

[0160] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu. 7.5 FeSn2S8.

[0161] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0162] Comparative Example 13

[0163] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6Fe. 1.5 Sn2S8.

[0164] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0165] Comparative Example 14

[0166] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6Sn2S8.

[0167] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0168] Comparative Example 15

[0169] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSnS8.

[0170] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0171] Comparative Example 16

[0172] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn. 2.5 S8.

[0173] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0174] Comparative Example 17

[0175] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn2S. 8.5 .

[0176] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0177] Comparative Example 18

[0178] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn2S. 4.5 .

[0179] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0180] Comparative Example 19

[0181] This embodiment provides a non-stoichiometric thermoelectric material with the chemical formula Cu6FeSn2S. 4.5 Se 3.5 .

[0182] The preparation method of the above-mentioned non-stoichiometric thermoelectric material is the same as that in Example 1, except that the raw materials are weighed according to the stoichiometric ratio of this embodiment. Therefore, it will not be repeated in this embodiment.

[0183] Experimental Example

[0184] 1. At room temperature, the thermoelectric materials prepared in Example 1 and Comparative Examples 1-5 were tested for their electrical transport properties (resistivity, Seebeck coefficient, and power factor), total thermal conductivity, lattice thermal conductivity, and dimensionless thermoelectric figure of merit. The results are shown in Table 1 and... Figures 3-6 .

[0185] Table 1. Electrotransport performance tests of thermoelectric materials in Example 1 and Comparative Examples 1-5

[0186] Resistivity (mΩ / cm) Seebeck coefficient (μV / K) <![CDATA[Power factor (μW / cmK 2 )]]> Example 1 2.09 84.78 3.44 Comparative Example 1 0.87 51.51 3.05 Comparative Example 2 0.85 50.76 3.03 Comparative Example 3 0.98 54.36 3.02 Comparative Example 4 4.24 105.07 2.60 Comparative Example 5 5.36 108.23 2.19

[0187] Conclusion: It is commonly believed that longer ball milling times lead to easier acquisition of single-phase samples. However, the inventors of this invention have discovered that this is not the case. Figure 2 ( Figure 2 The XRD diffraction patterns of the thermoelectric material after ball milling for 10, 20, 40, and 60 hours during the preparation of the thermoelectric material of the chemical formula in Example 2 are shown. It has been confirmed that a ball milling time of 10 hours is sufficient to synthesize a sample that meets the basic requirements. However, the inventors found through testing that the particle size of the material decreases rapidly in the first few hours of ball milling; further ball milling slows down the rate of particle size reduction but can still further refine the particle size. With prolonged ball milling, the microstructure of the sample becomes more uniform, and the electrical conductivity of the material generally increases. However, excessively long ball milling times can introduce more defects or impurities into the microstructure, thereby increasing resistivity. Specifically, in Figure 3 In the process of ball milling, thermoelectric material powders reach a nanocrystalline stable state after 10-30 hours, with grain boundary density approaching saturation and forming a stable point defect scattering network. However, with increasing ball milling time, a sharp drop in thermal conductivity occurs after 40 hours, indicating that prolonged ball milling induces amorphization in some regions. Figure 2 The significantly increased full width at half maximum (FWHM) at 25-30 degrees in the diffraction curves after 60 hours confirms this. Further extension of the ball milling time introduces more lattice defects, which enhance phonon scattering. Figure 4 In samples ball-milled for 40-60 hours, the lattice thermal conductivity continuously decreased. However, excessive amorphization led to a sharp drop in carrier mobility. Figure 5 In this study, the power factor actually decreased after ball milling for more than 40 hours, indicating that the performance gain from increasing the ball milling time became marginal. Considering all factors, a ball milling time of 40 hours was determined to be the optimal process window. Precise control of the ball milling time can effectively regulate the nanocrystalline or amorphous composite structure and defect distribution of the material. At this time, the thermal conductivity of the material is reduced to a relatively ideal level, achieving a balance between enhanced phonon scattering and carrier transport, ultimately resulting in a higher ZT value. Figure 6 As shown.

[0188] 2. Differential scanning calorimetry-thermogravimetric analysis was performed on the thermoelectric material prepared in Example 2. The results are shown in [reference needed]. Figure 7 The densities of the hot-pressed sintered samples (i.e., the thermoelectric materials prepared in Example 2 and Comparative Examples 6-10) at different temperatures are as follows: Figure 8 As shown.

[0189] Conclusion: The density increases with increasing sintering temperature, exceeding 95% at a sintering temperature of 650℃. Based on thermogravimetric analysis and differential scanning calorimetry (DSC) results, the material Cu6FeSn2S8 exhibits excellent thermal stability (weight loss <0.5wt%) within the temperature range of room temperature to 773K. The DSC curve showed no endothermic or exothermic peaks, confirming that no phase transformation or melting occurred within the test temperature range.

[0190] 3. At room temperature, the electrical transport properties (resistivity, Seebeck coefficient, and power factor) of the thermoelectric materials prepared in Examples 2-6 were tested, and the results are shown in Table 2.

[0191] Table 2. Electrotransport performance tests of thermoelectric materials in Examples 2-6

[0192] Resistivity (mΩ / cm) Seebeck coefficient (μV / K) <![CDATA[Power factor (μW / cmK 2 )]]> Example 2 212.75 294.19 0.41 Example 3 40.72 212.54 1.11 Example 4 26.48 158.40 0.95 Example 5 25.58 157.77 0.97 Example 6 30.13 142.97 0.68

[0193] Conclusion: The introduction of Cu vacancies usually increases the carrier concentration, leading to a decrease in Seebeck coefficient and resistivity. By reasonably controlling the number of Cu vacancies, the electrical properties of thermoelectric materials can be optimized, thereby improving their thermoelectric figure of merit.

[0194] 4. At room temperature, the thermoelectric materials prepared in Examples 1-2 and 7-10 were tested for their electrical transport properties (resistivity, Seebeck coefficient, and power factor). The results are shown in Table 3.

[0195] Table 3. Electrotransport performance tests of thermoelectric materials in Examples 1-2 and 7-10.

[0196]

[0197]

[0198] Conclusion: Cu6FeSn2S8 exhibits relatively high thermal conductivity, and its thermoelectric properties can be optimized by introducing Fe vacancies. The introduction of Fe vacancies typically increases carrier concentration, thereby reducing resistivity, but the effect on the Seebeck coefficient depends on the specific material system and defect concentration. By rationally controlling the number of Fe vacancies, the electrical properties of the material can be optimized, thus improving its thermoelectric figure of merit. The introduction of Fe vacancies generally decreases the Seebeck coefficient of the material. This is because the introduction of Fe vacancies increases carrier concentration, thereby reducing the Seebeck coefficient. With increasing Fe vacancy concentration, the Seebeck coefficient decreases at room temperature with increasing defect concentration. These point defects can enhance phonon scattering, thereby reducing lattice thermal conductivity. In this way, the thermoelectric properties of the material can be effectively improved, as lower thermal conductivity contributes to a higher thermoelectric figure of merit. When b is 0.375, the power factor is the largest, and the contribution of electronic thermal conductivity to the total thermal conductivity is extremely low; therefore, the quality factor is also the largest, i.e., Cu6Fe 0.375 Sn2S8 has the largest quality factor.

[0199] 5. At room temperature, the thermoelectric materials prepared in Examples 2 and 11-14 were tested for electrical transport properties (resistivity, Seebeck coefficient, and power factor). The results are shown in Table 4.

[0200] Table 4. Electrical transport performance tests of thermoelectric materials in Examples 2 and 11-14

[0201] Resistivity (mΩ / cm) Seebeck coefficient (μV / K) <![CDATA[Power factor (μW / cmK 2 )]]> Example 2 212.75 294.19 0.41 Example 11 38.75 205.86 1.09 Example 12 19.40 119.91 0.74 Example 13 27.45 124.03 0.56 Example 14 15.63 118.92 0.90

[0202] Conclusion: The absence of Sn may lead to local lattice distortion. As can be seen from the table above, the Seebeck coefficient and resistivity gradually decrease, but the power factor shows fluctuating changes.

[0203] 6. After sanding the carbon paper on the surface of the thermoelectric materials prepared in Examples 2 and 15-17 with sandpaper, phase identification and microstructure characterization were performed, and performance tests were conducted. The results are shown in [reference needed]. Figure 9 and Figure 10 , Figure 9 This is an X-ray diffraction pattern. Figure 10 The images shown are cross-sectional scanning electron microscope (SEM) images. The thermoelectric materials prepared in Examples 2 and 15-17 were tested for electrical transport properties (resistivity, Seebeck coefficient, and power factor), total thermal conductivity, and dimensionless thermoelectric figure of merit. The results are shown below. Figures 11-15 .

[0204] in conclusion: Figure 9 This indicates that the prepared material has high purity and no obvious impurity peaks. Furthermore, as the doping concentration increases, the main diffraction peak shifts to a lower angle, suggesting that larger Se atoms successfully replace S atoms, and the lattice constant gradually increases. Figure 10 In the sample with x=3, the pore size was approximately 1 μm. The pore size gradually decreased with increasing doping concentration. This may be because the excessive addition of Se compensated for high-temperature volatilization losses, preserving some point defects and effectively reducing thermal conductivity. Figures 11 to 15 It can be seen that the resistivity of the high-Se sample decreases with increasing temperature, which is lower than that of the low-Se sample. Irreversible volatilization of Se at high temperatures leads to changes in the microstructure. The Seebeck coefficient of the high-Se sample fluctuates but lacks a regularity, while the Seebeck coefficient of other samples generally shows a trend of first decreasing and then increasing with increasing temperature. With increasing Se doping concentration, the total thermal conductivity decreases with increasing temperature, showing a significant decrease compared to the undoped Se sample. The dimensionless thermoelectric figure of merit increases with increasing temperature, with a substantial increase in the doped sample, reaching 0.32 at 750 K when x = 2.

[0205] 7. The electrical transport properties (resistivity, Seebeck coefficient, and power factor) of the thermoelectric materials prepared in Examples 15, 18-21 were tested.

[0206] The results of tests on total thermal conductivity, lattice thermal conductivity, and dimensionless thermoelectric figure of merit are shown in [reference needed]. Figures 16-21 .

[0207] Conclusion: From Figures 16 to 21It can be seen that when 6 ≤ a < 6.8 and 0.2 < b ≤ 1, the resistivity of the sample decreases with temperature, exhibiting semiconductor characteristics. Overfilling of Cu leads to a transformation of the sample towards metallic properties. This can be attributed to the formation of new defects by excess Cu, which become ionization scattering centers, increasing the scattering probability between electrons and causing a significant decrease in mobility with increasing temperature. The Seebeck coefficient increases with increasing temperature; the power factor increases with increasing temperature; the thermal conductivity decreases with increasing temperature; the lattice thermal conductivity decreases with increasing temperature; the dimensionless thermoelectric figure of merit (ZT) increases with increasing temperature. When a = 6.8 and b = 0.2, the thermoelectric figure of merit reaches 0.78 at 750 K, at which point the power factor is 6.12 μW / cm². -1 K -2 The lattice thermal conductivity is 0.37 W / m². -1 K -1 .

[0208] 8. At room temperature, the electrical transport properties (resistivity, Seebeck coefficient, and power factor) of the thermoelectric materials prepared in Comparative Examples 11-19 were tested, and the results are shown in Table 5.

[0209] Table 5. Electrotransport performance tests of thermoelectric materials in Comparative Examples 11-19

[0210] Resistivity (mΩ / cm) Seebeck coefficient (μV / K) <![CDATA[Power factor (μW / cmK 2 )]]> Comparative Example 11 97.24 174.27 0.31 Comparative Example 12 226.71 514.81 1.17 Comparative Example 13 86.79 162.49 0.30 Comparative Example 14 0.26 15.44 0.92 Comparative Example 15 90.44 211.92 0.50 Comparative Example 16 560.95 296.87 0.16 Comparative Example 17 86.70 228.18 0.60 Comparative Example 18 1.25 -16.45 0.22 Comparative Example 19 108.84 114.14 0.12

[0211] Conclusion: When x > 3, a degenerate semiconductor is formed, leading to a sharp decrease in the Seebeck coefficient. Increased carrier concentration induces ionized impurity scattering, resulting in decreased mobility. When a < 4, as... Figure 22 Excessive Cu vacancies easily lead to the precipitation of Cu₂S or FeS impurity phases, disrupting the single-phase nature and significantly impacting the thermoelectric properties of the material. When a > 7, a large number of Cu ions are precipitated, causing a sharp increase in Seebeck's coefficient and resistivity. When b = 0, the chemical formula becomes Cu₆Sn₂S₈, with almost complete absence of Fe, but the main phase structure is still maintained according to XRD, with only trace amounts of SnS impurity phase appearing. The Sn interstitial spaces and S vacancies introduce high-concentration electrons, and the bipolar conduction effect reduces the Seebeck effect. When b > 1, Fe… 2+The addition of extra electrons, manifested as n-type doping, increases carrier concentration and thus decreases resistivity. When c < 1.5, ordered vacancies in Sn form electron potential traps, creating vacancy clusters. This localization causes a sharp drop in carrier mobility. Simultaneously, local Sn aggregation and precipitation of the SnS impurity phase introduce an energy filtering effect, increasing the Seebeck coefficient. Sn has limited solubility; excess Sn may precipitate as metallic Sn particles or Cu2SnS3 impurity phases. Interstitial Sn atoms act as donor levels (electron providers) and recombine with vacancies (p-type) in the main phase, effectively reducing carrier concentration. The quality factor also drops sharply due to excessively high resistivity. Furthermore, this invention also found that when the S content exceeds the stoichiometry (greater than 8), excess S further exacerbates S volatilization and simultaneously generates impurity phases such as FeS2 and elemental S, causing the sintered composition to deviate from the design value. When the S content is too low (less than 5), each missing S atom releases two electrons, causing the material to transform from p-type to n-type. In the sintering process, we found that when the temperature is raised to 650℃, the sample develops a large number of macroscopic cracks and the metallic luster decreases, making it unable to maintain its bulk morphology. This is due to the formation of low-melting-point impurity phases in the material.

[0212] In summary, this invention produces thermoelectric materials with excellent thermoelectric properties through cation vacancy regulation, Se solid solution, and Cu supersaturation. These materials effectively improve electrical conductivity and power factor, reduce lattice thermal conductivity, and significantly enhance their dimensionless thermoelectric figure of merit. Furthermore, the use of mechanical alloying combined with vacuum hot pressing sintering yields even better thermoelectric properties.

[0213] Although the principles of the present invention have been described in detail above with reference to preferred embodiments, those skilled in the art should understand that the above embodiments are merely illustrative explanations of the implementation of the present invention and are not intended to limit the scope of the present invention. The details in the embodiments do not constitute a limitation on the scope of the present invention. Any obvious changes, such as equivalent transformations or simple substitutions, based on the technical solutions of the present invention without departing from the spirit and scope of the present invention fall within the protection scope of the present invention.

Claims

1. A non-stoichiometric thermoelectric material, characterized in that, The general chemical formula of the thermoelectric material is Cu. a Fe b Sn c S 8-x Se x ; Wherein, 4≤a<7, 0<b≤1, 1.5≤c≤2, 0≤x≤3, and a, b, c and x are atomic ratios respectively.

2. The non-stoichiometric thermoelectric material according to claim 1, characterized in that, When x is 0, then 4≤a≤6, 0.25≤b≤1, and 1.5≤c≤2.

3. The non-stoichiometric thermoelectric material according to claim 1, characterized in that, When a is 6, then b is 1, c is 2, and 0 ≤ x ≤ 3.

4. The non-stoichiometric thermoelectric material according to claim 1, characterized in that, When x is 2, then 6 ≤ a < 7, 0 < b ≤ 1, c is 2, and a + b = 7.

5. The non-stoichiometric thermoelectric material according to claim 1, characterized in that, The thermoelectric material has the chemical formula Cu6FeSn2S8, Cu 5.5 FeSn2S8, Cu5FeSn2S8, Cu 4.5 FeSn2S8, Cu4FeSn2S8, Cu6Fe 0.75 Sn2S8, Cu6Fe 0.625 Sn2S8, Cu6Fe 0.5 Sn2S8, Cu6Fe 0.375 Sn2S8, Cu6Fe 0.25 Sn2S8, Cu6FeSn 1.875 S8, Cu6FeSn 1.75 S8, Cu6FeSn 1.625 S8, Cu6FeSn 1.5 S8, Cu6FeSn2S7Se1, Cu6FeSn2S6Se2, Cu6FeSn2S5Se3, Cu 6.4 Fe 0.6 Sn2S6Se2, Cu 6.7 Fe 0.3 Sn2S6Se2, Cu 6.8 Fe 0.2 Sn2S6Se2 or Cu 6.9 Fe 0.1 Sn2S6Se2.

6. The non-stoichiometric thermoelectric material according to claim 1, characterized in that, The chemical formula of the thermoelectric material is Cu. 6.8 Fe 0.2 Sn2S6Se2 or Cu6Fe 0.375 Sn2S8.

7. A method for preparing a non-stoichiometric thermoelectric material according to any one of claims 1-6, characterized in that, Includes the following steps: According to the atomic ratio of each element in the thermoelectric material, Cu elemental powder, Fe elemental powder, Sn elemental powder, S elemental powder and Se elemental powder are weighed respectively. Under a protective gas atmosphere, the raw materials are mixed and then ball-milled, sintered, and finally polished to obtain the thermoelectric material. The ball milling time is 35-45 hours.

8. The method for preparing a non-stoichiometric thermoelectric material according to claim 7, characterized in that, During the ball milling process, the mass ratio of grinding balls to raw materials is 40-50:1, and the milling speed is 450 rpm; and / or, The purity of the Cu, Fe, and Se elemental powders is ≥99.9%, and the purity of the Sn and S elemental powders is ≥99.99%.

9. The method for preparing a non-stoichiometric thermoelectric material according to claim 7, characterized in that, The sintering method is as follows: the ball-milled powder is heated from room temperature to 500°C at a heating rate of 10°C / min, and the longitudinal pressure is increased to 15 MPa within 2 minutes; then the temperature is increased from 500°C to 650°C, and the longitudinal pressure is increased from 15 MPa to 35 MPa within 2 minutes; finally, sintering is carried out at 650°C for 1 hour; and / or, The protective gas is an argon-hydrogen mixture, in which the volume fraction of argon is 92% and the volume fraction of hydrogen is 8%.

10. The application of a non-stoichiometric thermoelectric material according to any one of claims 1-6 in a thermoelectric power generation and refrigeration device in the temperature range of 300-750K.

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