A kind of vacancy filling type hessle thermoelectric material and its preparation method

Abstract

The present application relates to a kind of vacancy filling type Hesler thermoelectric material and its preparation method, its chemical formula is: Nb 0.75 Ti 0.25 FeCr x Sb, wherein x is in the range of 0≤x≤0.1;Using high-energy ball milling (HEBM) and spark plasma sintering (SPS) and annealing method, pure phase with Hesler structure is prepared, the alloy shows excellent thermoelectric properties similar to semiconductor type half Hesler alloy, wherein x=0.1 composition exists the highest zT value, and reaches maximum 1.21 at 973K. It shows that vacancy filling as the effectiveness of optimization HH compound thermoelectric performance strategy. The successful combination of low thermal conductivity and high electrical performance in the compound provides a promising way for the development of advanced thermoelectric materials.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric materials technology, and in particular to a vacancy-filled Hessler thermoelectric material and its preparation method. Background Technology

[0002] Energy and the environment are among the two major challenges facing the world today, and also crucial issues for human societal development. Energy is the foundation of modern social development and production activities, while the environment is the fundamental condition for human survival. However, excessive energy consumption and environmental pollution brought about by scientific and technological development have triggered numerous problems, such as global climate change, air and water pollution, which have severely impacted human survival and development. Therefore, it is urgent to develop renewable energy sources and improve energy efficiency.

[0003] Thermoelectric materials, also known as thermoelectric materials, are semiconductor functional materials that achieve direct energy conversion between heat and electricity based on the Seebeck and Peltier effects. Compared with traditional refrigeration and power generation, thermoelectric conversion technology has advantages such as quiet operation, environmental friendliness, and high reliability. It is widely used, particularly in industrial waste heat power generation, engine waste heat recovery, and automobile exhaust waste heat recovery. Research on thermoelectric materials is not only significant for improving energy efficiency and achieving sustainable energy development, but also for promoting the development of materials science. In thermoelectric material systems, the dimensionless thermoelectric figure of merit zT can be used to evaluate the thermoelectric performance of a material; the value of zT determines the efficiency of refrigeration and power generation during application. Typically, zT = S. 2 σT / κ, where S, σ, κ, and T are the Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature of the environment, respectively.

[0004] Hessler alloys have attracted increasing interest due to their wide range of applications and intriguing physical properties. Among them, half-Hessler (HH) alloys, with 18 valence electrons, are semiconductors according to the Slater-Pauling rule. Due to their superior electrical and mechanical properties, as well as excellent thermal stability, they are considered ideal thermoelectric materials for medium- and high-temperature applications. In recent years, research progress on HH thermoelectric materials has garnered significant attention. This includes the development of double-HH alloys and HH alloys with intrinsic defects, such as TiFe. 0.5 Ni 0.5 Sb and Nb 0.8 CoSb alloys, these alloys have 18 valence electrons. Another class of interest are vacancy-filled Heusler alloys, which are compositionally intermediate between HH and FH. Due to their unique crystal and electronic structure, vacancy-filled Heusler compounds possess unique physical and thermoelectric properties, such as anomalous density of states effective mass and extremely low lattice thermal conductivity.

[0005] Chinese patent CN202310264735.4 discloses a P-type Hessler-like thermoelectric material and its preparation method, with the chemical formula: TiFe x Cu 2x-1 Sb, where x ranges from 0.67 to 1; a pure phase with a Hessler-like structure was prepared using high-energy ball milling (HEBM) and spark plasma sintering (SPS). This alloy exhibits excellent thermoelectric properties similar to those of semiconductor-type semi-Hessler alloys, with the highest zT value found in the x = 0.7 composition, reaching a maximum of 0.75 at 973 K. Low-temperature physical property tests revealed that its low-temperature heat capacity (Cel) and resistivity (ρ) change with temperature in a manner completely similar to those of non-Fermi liquid metal systems, indicating that this alloy also possesses characteristics of non-Fermi liquid metals. Summary of the Invention

[0006] The purpose of this invention is to provide a vacancy-filled Hessler thermoelectric material and its preparation method. By doping at interstitial sites and adjusting the atomic content, the ideal characteristics of low lattice thermal conductivity and high density of states effective mass present in vacancy-filled Hessler alloys are combined with the existing characteristics of traditional 18-valent electron HH alloys. The aim is to invent an effective strategy to optimize the thermoelectric performance of traditional HH alloys.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A vacancy-filled Hessler thermoelectric material, the vacancy-filled Hessler thermoelectric material being composed of a basic framework and filling atoms, the filling atoms being located in the gaps of the basic framework;

[0009] The basic framework has the chemical formula Nb y Ti z FeSb, where y ranges from 0.75 to 1 and z ranges from 0 to 0.25, the filling atom is Cr atom, and the vacancy-filled Hessler thermoelectric material structure is as follows: Figure 1 As shown.

[0010] Furthermore, the basic framework has a tetrahedral structure, and the filling atoms are located in the gaps between the tetrahedrons.

[0011] Furthermore, the Cr atom has 6 valence electrons.

[0012] Furthermore, the chemical formula of the basic framework is Nb. 0.75 Ti 0.25 FeSb.

[0013] Furthermore, the chemical formula of the vacancy-filled Hessler thermoelectric material is: Nb 0.75 Ti 0.25 FeCrx Sb, where x takes values ​​in the range 0 ≤ x ≤ 0.1.

[0014] Furthermore, in the above chemical formula, x = 0.02, 0.06, 0.1.

[0015] Furthermore, the electrical conductivity of the vacancy-filled Hessler thermoelectric material is between 85,000 and 365,000 S / m, the Seebeck coefficient is between 94 and 220 μV / K, and the power factor is between 33.6 and 44.5 μW / (cm·K). 2 The thermal conductivity is between 3.47 and 7.15 W / (m·K), and the zT value is between 0.15 and 1.21.

[0016] Furthermore, in the aforementioned chemical formula, x = 0.1, and the highest power factor at 973 K is 43.2 μW / (cm·K). 2 The lowest thermal conductivity is 3.47 W / (m·K), and the highest zT is 1.21.

[0017] Furthermore, this invention also provides a method for preparing a vacancy-filled Hessler thermoelectric material, using elemental Nb sheets, Ti sheets, Fe sheets, Cr particles, and Sb particles as raw materials, prepared by high-energy ball milling (HEBM) and spark plasma sintering (SPS), and annealed at 973 K for 7 days to obtain the vacancy-filled Hessler thermoelectric material, whose chemical formula is: Nb 0.75 Ti 0.25 FeCr x Sb, where x takes values ​​in the range 0 ≤ x ≤ 0.1.

[0018] Furthermore, the preparation method of the vacancy-filled Hessler thermoelectric material includes the following specific steps:

[0019] S1. Calculation: Based on the stoichiometric ratio of Nb:Ti:Fe:Cr:Sb = 0.75:0.25:1:x:1, calculate the mass of each element corresponding to a specific x value.

[0020] S2. Sample preparation: Weigh the elemental Nb flakes, Ti flakes, Fe flakes, Cr particles, and Sb particles according to the mass calculated in step S1, and place the weighed raw materials in a stainless steel ball mill jar.

[0021] S3, Alloying: The ball mill jar from step S2 is placed in a high-energy ball mill and subjected to continuous ball milling and material collision for a long time to obtain mixed powder;

[0022] S4. Sintering: Weigh a certain amount of the mixed powder obtained in step S3 into a graphite mold, then place the mold into a spark plasma sintering equipment, evacuate it and apply a certain pressure to start sintering, and finally hold it at a certain temperature for a period of time, then release the pressure and let it cool naturally to room temperature to obtain a preliminary sample.

[0023] S5. Annealing: The preliminary sample obtained by sintering in step S4 is subjected to high-temperature annealing to obtain vacancy-filled Hessler thermoelectric material.

[0024] Furthermore, in step S1, the total amount of raw materials weighed is generally 0.04 mol. The required mass of each element can be calculated by using the formula m = n × M (n: the molar amount of a certain element under a specific composition, m: the required mass, M: the atomic molar mass) and the stoichiometric ratio of the corresponding composition.

[0025] Furthermore, in step S2, in an argon glove box, the elemental Nb flakes, Ti flakes, Fe flakes, Cr particles, and Sb particles are weighed according to the mass calculated in step S1.

[0026] The purity of the elemental Nb flakes, Ti flakes, Fe flakes, Cr particles, and Sb particles are 99.95%, 99.6%, 99.95%, 99.99%, and 99.999%, respectively.

[0027] Furthermore, in step S3, the obtained mixed powder is stored in an argon glove box.

[0028] The ball mill is set to a milling time of 20-30 hours, preferably 28 hours, to ensure that the raw materials are fully mixed and completely milled into powder.

[0029] Furthermore, in step S4, the sintering gas pressure is 58-62 MPa, the applied pressure is 6-6.5 kN, the temperature is raised to 900℃ at a sintering rate of 30-50℃ / min, and the holding time is 10-15 min.

[0030] Furthermore, the sintering pressure is 60 MPa, the applied pressure is 6.3 kN, the temperature is raised to 900℃ in 20 minutes at a sintering rate of 30-50℃ / min, and the holding time is 10-15 minutes.

[0031] Furthermore, in step S4, the graphite mold has a diameter of 12.7 mm, and after sintering, a circular thermoelectric material with a thickness of 1-2 mm is obtained.

[0032] Furthermore, in step S5, the annealing temperature is 900–1000 K, preferably 973 K; and the annealing time is 6–8 days, preferably 7 days.

[0033] This invention first constructs a vacancy-filled Hessler framework. Typically, this type of vacancy-filled Hessler structure appears in 17-valent electron HH alloys. However, this invention uses an 18-valent electron NbFeSb alloy as the basic framework for a vacancy-filled Hessler thermoelectric material. By introducing suitable filling atoms at the 4d position of its crystal structure, the aim is to invent a novel Hessler compound with high thermoelectric performance. To this end, the following attempts were made in this experiment:

[0034] In 17-valent electron HH alloys, attempts to fill interstitial positions with only suitable atoms can result in the formation of a stable pure phase. However, this compound can only form a stable pure phase under specific compositions and exhibits low performance. This invention aims to combine the ideal characteristics of low lattice thermal conductivity and high density of states effective mass present in vacancy-filled Hessler alloys with the existing properties of traditional 18-valent electron HH alloys, thereby inventing a vacancy-filled Hessler alloy with excellent thermoelectric properties. Since 18-valent electron HH alloys inherently possess a stable crystal structure, while the selection of additional filling atoms is highly random and the phase stability is unknown, this invention employs the Slater-Pauling rule for the study of this type of Hessler alloy system. According to the Slater-Pauling rule, when the average number of valence electrons of all atoms is 6, a non-magnetic, stable Hessler compound can be formed. For 18-valent electron NbFeSb, when filled with Cr atoms with 6 valence electrons, NbFeCr... x The average number of valence electrons in Sb compounds remains 6, meaning that this type of vacancy-filled Hessler alloy with 18 valence electrons (HH) is stable. Furthermore, according to the Slater-Pauling rule, the introduction of Cr atoms does not change the carrier concentration of the system, which facilitates the optimization of thermoelectric properties. A simple application of the Slater-Pauling rule shows that filling interstitial positions with Cr atoms does not affect the stability of the compound, but there is a limit to the actual amount of Cr atoms that can be filled. In addition, for NbFeSb, 25% Ti doping can adjust its carrier concentration to the optimal level, ultimately resulting in its chemical formula Nb. 0.75 Ti 0.25 FeCr x Sb, where 0 ≤ x ≤ 0.1. This invention has discovered that filling atoms in this ratio can form a stable phase, such as... Figure 2 As shown, all synthesized samples are pure phases with a Hessler-like structure.

[0035] To achieve the above-mentioned objectives, this invention employs a mechanical alloying method in the alloy preparation process. This method not only avoids the problem of Sb volatilization but also reduces preparation time. The mechanically alloyed powder is then stabilized through rapid sintering, ensuring a shorter alloy preparation process while retaining more grain boundaries to further reduce thermal conductivity.

[0036] The concepts involved in this invention may not be applicable only to the system mentioned in the present invention. Combining different 18-valent electron HHs and filling atoms may lead to the exploration of more high-performance HH thermoelectric materials, thereby broadening the Hessler alloy system and accelerating its development and application.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] 1. This invention uses high-energy ball milling (HEBM), spark plasma sintering (SPS), and annealing to prepare a pure phase with a Hessler-like structure. This process is convenient to operate and has a short preparation time.

[0039] 2. This invention is not a traditional stoichiometric HH compound, but a novel vacancy-filled Hessler alloy that exhibits excellent thermoelectric properties similar to those of a semi-semiconductor Hessler alloy. The composition with x = 0.1 has the highest zT value, which reaches a maximum of 1.21 at 973 K, demonstrating the effectiveness of vacancy filling as a strategy for optimizing the thermoelectric properties of HH compounds.

[0040] 3. In selecting the interstitial filling atoms, this invention attempted the Slater-Pauling rule and found a component with better performance within a certain component range.

[0041] 4. This invention eliminates the need for expensive and challenging process elements such as Hf and Ta. This not only simplifies the manufacturing process but also opens up possibilities for the wide industrial application of HH alloy-based thermoelectric devices.

[0042] 5. The material of this invention has a unique crystal structure and exhibits excellent thermoelectric properties. The successful combination of low thermal conductivity and high electrical properties in this compound provides a promising path for the development of advanced thermoelectric materials. Attached Figure Description

[0043] Figure 1 Nb in Embodiments 1-3 of the present invention 0.75 Ti 0.25 FeCr x Structural diagram of Sb-based thermoelectric materials;

[0044] Figure 2 Nb in Embodiments 1-3 of the present invention 0.75 Ti 0.25 FeCr x X-ray diffraction pattern of Sb-based thermoelectric materials;

[0045] Figure 3 Nb in Embodiments 1-3 of the present invention 0.75 Ti 0.25FeCr x Schematic diagram of the electrical conductivity of Sb-based thermoelectric materials as a function of temperature;

[0046] Figure 4 Nb in Embodiments 1-3 of the present invention 0.75 Ti 0.25 FeCr x Schematic diagram of room temperature carrier concentration in Sb-based thermoelectric materials;

[0047] Figure 5 Nb in Embodiments 1-3 of the present invention 0.75 Ti 0.25 FeCr x Schematic diagram of Seebeck coefficient versus temperature for Sb-based thermoelectric materials;

[0048] Figure 6 Nb in Embodiments 1-3 of the present invention 0.75 Ti 0.25 FeCr x Schematic diagram of the power factor of Sb-based thermoelectric materials as a function of temperature;

[0049] Figure 7 Nb in Embodiments 1-3 of the present invention 0.75 Ti 0.25 FeCr x Schematic diagram of the thermal conductivity of Sb-based thermoelectric materials as a function of temperature;

[0050] Figure 8 Nb in Embodiments 1-3 of the present invention 0.75 Ti 0.25 FeCr x Schematic diagram of the zT value of Sb-based thermoelectric materials as a function of temperature. Detailed Implementation

[0051] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0052] The following detailed description of some embodiments of the present invention is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0053] Example 1

[0054] This embodiment provides a high-performance vacancy-filled Hessler thermoelectric material with the chemical formula Nb. 0.75 Ti 0.25 FeCr 0.02 Sb.

[0055] Furthermore, this embodiment also provides a high-performance vacancy-filled Hessler thermoelectric material Nb 0.75 Ti 0.25 FeCr 0.02 The preparation method of Sb involves high-energy ball milling (HEBM), spark plasma sintering (SPS), and annealing synthesis. The specific steps are as follows:

[0056] a. Calculation: Based on the stoichiometric ratio of Nb:Ti:Fe:Cr:Sb = 0.75:0.25:1:0.02:1 and the formula m = n × M, calculate 0.04 mol Nb 0.75 Ti 0.25 FeCr 0.02 The required mass of each element for Sb;

[0057] b. Sample preparation: In an argon glove box, weigh the Nb flakes with a purity of 99.95%, Ti flakes with a purity of 99.6%, Fe flakes with a purity of 99.95%, Cr granules with a purity of 99.99%, and Sb granules with a purity of 99.99%, according to the mass calculated in step a, on an electronic balance with an accuracy of 0.1 mg, and place the weighed raw materials into a stainless steel ball mill jar;

[0058] c. Alloying: The ball mill jar from step b is placed in a high-energy ball mill, and mixed powder is obtained by continuous and uninterrupted collision of balls and materials for 28 hours;

[0059] d. Sintering: The mixed powder obtained in step c is stored in an argon glove box. 1-1.5 grams of powder are weighed and placed in a graphite mold with a diameter of 12.7 mm. The mold is then placed in a spark plasma sintering (SPS) apparatus and a vacuum is applied. When the vacuum chamber pressure is approximately 60 MPa, a pressure of 6.3 kN is slowly applied to the sample to begin sintering. The sintering rate is 30-50 °C / min, reaching 900 °C in 20 minutes. After holding at this temperature for 10-15 minutes, the pressure is released, and the sample is allowed to cool naturally to room temperature, yielding Nb alloys with a diameter of 12.7 mm and a thickness of 1-2 mm. 0.75 Ti 0.25 FeCr 0.02 Sb test disc.

[0060] e. Annealing: The preliminary sample obtained by sintering was annealed at 973K for 7 days to obtain the thermoelectric material Nb. 0.75 Ti 0.25 FeCr 0.02 Sb.

[0061] Example 2

[0062] This embodiment is basically the same as the previous embodiments, except that:

[0063] This embodiment provides a high-performance vacancy-filled Hessler thermoelectric material with the chemical formula Nb. 0.75 Ti 0.25 FeCr 0.06 Sb.

[0064] Furthermore, this embodiment also provides a high-performance vacancy-filled Hessler thermoelectric material Nb 0.75 Ti 0.25 FeCr 0.06 The preparation method of Sb involves high-energy ball milling (HEBM), spark plasma sintering (SPS), and annealing synthesis. The specific steps are as follows:

[0065] a. Calculation: Based on the stoichiometric ratio of Nb:Ti:Fe:Cr:Sb = 0.75:0.25:1:0.06:1 and the formula m = n × M, calculate 0.04 mol Nb 0.75 Ti 0.25 FeCr 0.06 The required mass of each element for Sb;

[0066] b. Sample preparation: This step is consistent with Example 1;

[0067] c. Alloying: This step is consistent with Example 1;

[0068] d. Sintering: The mixed powder obtained in step c is stored in an argon glove box. 1-1.5 grams of powder are weighed and placed in a graphite mold with a diameter of 12.7 mm. The mold is then placed in a spark plasma sintering (SPS) apparatus and a vacuum is applied. When the vacuum chamber pressure is approximately 60 MPa, a pressure of 6.3 kN is slowly applied to the sample to begin sintering. The sintering rate is 30-50 °C / min, reaching 900 °C in 20 minutes. After holding at this temperature for 10-15 minutes, the pressure is released, and the sample is allowed to cool naturally to room temperature, yielding Nb alloys with a diameter of 12.7 mm and a thickness of 1-2 mm. 0.75 Ti 0.25 FeCr 0.06 Sb test disc.

[0069] e. Annealing: The preliminary sample obtained by sintering was annealed at 973K for 7 days to obtain the thermoelectric material Nb. 0.75 Ti 0.25 FeCr 0.06 Sb.

[0070] Example 3

[0071] This embodiment is basically the same as the previous embodiments, except that:

[0072] This embodiment provides a high-performance vacancy-filled Hessler thermoelectric material with the chemical formula Nb.0.75 Ti 0.25 FeCr 0.1 Sb.

[0073] Furthermore, this embodiment also provides a high-performance vacancy-filled Hessler thermoelectric material Nb 0.75 Ti 0.25 FeCr 0.1 The preparation method of Sb involves high-energy ball milling (HEBM), spark plasma sintering (SPS), and annealing synthesis. The specific steps are as follows:

[0074] a. Calculation: Based on the stoichiometric ratio of Nb:Ti:Fe:Cr:Sb = 0.75:0.25:1:0.1:1 and the formula m = n × M, calculate 0.04 mol Nb 0.75 Ti 0.25 FeCr 0.1 The required mass of each element for Sb;

[0075] b. Sample preparation: This step is consistent with Example 1;

[0076] c. Alloying: This step is consistent with Example 1;

[0077] d. Sintering: The mixed powder obtained in step c is stored in an argon glove box. 1-1.5 grams of powder are weighed and placed in a graphite mold with a diameter of 12.7 mm. The mold is then placed in a spark plasma sintering (SPS) apparatus and a vacuum is applied. When the vacuum chamber pressure is approximately 60 MPa, a pressure of 6.3 kN is slowly applied to the sample to begin sintering. The sintering rate is 30-50 °C / min, reaching 900 °C in 20 minutes. After holding at this temperature for 10-15 minutes, the pressure is released, and the sample is allowed to cool naturally to room temperature, yielding Nb alloys with a diameter of 12.7 mm and a thickness of 1-2 mm. 0.75 Ti 0.25 FeCr 0.1 Sb test disc.

[0078] e. Annealing: The preliminary sample obtained by sintering was annealed at 973K for 7 days to obtain the thermoelectric material Nb. 0.75 Ti 0.25 FeCr 0.1 Sb.

[0079] Experimental test analysis:

[0080] X-ray diffraction patterns of the thermoelectric materials obtained in Examples 1-3 were obtained using a Rigaku SmartLab-II diffractometer. The X-ray source used for the tests was Cu-K. α The test sample was in powder form.

[0081] The thermoelectric materials obtained in Examples 1 to 3 were all tested for electrical properties, including resistivity and Seebeck coefficient, on the ULVAC-RIKO ZEM-3 equipment.

[0082] The thermoelectric materials obtained in Examples 1-3 were all subjected to electrical performance tests on a NETZSCH LFA 457 instrument, primarily testing the thermal diffusivity D. The thermal conductivity is calculated using the formula κ = DC. p ρ, where C p ρ is the heat capacity of the material, which can be estimated using the Dulong-Petty law, while ρ is the density of the material, which can be estimated using Archimedes' method of displacement.

[0083] The thermoelectric materials obtained in Examples 1-3 were tested for room temperature carrier concentration using a Physical Property Measurement System (PPMS).

[0084] Figure 3-8 The graph shows the thermoelectric performance test results of the thermoelectric materials obtained in Examples 1-3. The conductivity of all tested samples decreased continuously with increasing temperature, exhibiting heavily doped semiconductor behavior. Furthermore, the conductivity decreased with increasing filler atomic content. Notably, the carrier concentration of all samples remained unchanged, consistent with the Slater-Pauling rule. The Seebeck coefficient of the corresponding tested samples increased with increasing temperature, and all samples exhibited a positive Seebeck coefficient, indicating that they were all hole-dominated P-type conductors.

[0085] The thermal conductivity of all tested samples decreased monotonically with temperature, indicating that bipolar diffusion was not observed. The trend is likely a result of various scattering mechanisms, including phonon-phonon scattering, point defect scattering, and grain boundary scattering. Unlike conventional HH alloys, this vacancy-filled Hessler alloy has partially filled 4d positions, with additional point defects further scattering phonons, reducing lattice thermal conductivity and enhancing its thermoelectric properties. Analysis of the tested samples revealed that the overall thermal conductivity was not high. Compared to the intrinsic stoichiometric thermal conductivity of HH compounds (10-15 W / (m·K), the thermal conductivity of the samples tested in this invention ranged from 3.47 to 7.15 W / (m·K).

[0086] Based on the test results, it can be seen that the thermoelectric performance gradually increases with the increase of Cr atom content in the interstitial positions, among which Nb... 0.75 Ti 0.25 FeCr 0.1 Sb alloys exhibit the best performance: electrical conductivity between 85,000 and 255,000 S / m; Seebeck coefficient between 120 and 220 μV / K; and power factor between 37.5 and 44.5 μW / (cm·K). 2The thermal conductivity is between 3.47 and 5.4 W / (m·K); the zT value is between 0.23 and 1.21. Thanks to the larger power factor and lower thermal conductivity at high temperatures, the zT value is also the highest at 973 K, reaching 1.21.

[0087] In summary, this invention utilizes high-energy ball milling (HEBM), spark plasma sintering (SPS), and annealing to efficiently synthesize Nb. 0.75 Ti 0.25 FeCr x Sb (x = 0.02, 0.06, 0.1) is a vacancy-filled Hessler alloy with pure phases. These alloys exhibit high Seebeck coefficients, high electrical conductivity, and low thermal conductivity. Among them, Nb... 0.75 Ti 0.25 FeCr 0.1 Sb alloys exhibit the highest thermoelectric properties, with a power factor of 43.2 μW / (cm·K) at 973 K. 2 The lowest thermal conductivity is 3.47 W / (m·K), and the highest zT is 1.21.

[0088] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A vacancy-filled Hessler thermoelectric material, characterized in that, The vacancy-filled Hessler thermoelectric material consists of a basic framework and filling atoms, wherein the filling atoms are located at the 4d position of the crystal structure and are Cr atoms. The chemical formula of the vacancy-filled Hessler thermoelectric material is Nb. y Ti z FeCr x Sb, where y takes values ​​in the range of 0.75 ≤ y ≤ 1, z takes values ​​in the range of 0 ≤ z ≤ 0.25, and x takes values ​​in the range of 0. <x≤0.1。 2. The vacancy-filled Hessler thermoelectric material according to claim 1, characterized in that, The chemical formula of the vacancy-filled Hessler thermoelectric material is Nb. 0.75 Ti 0.25 FeCr x Sb, where x takes values ​​ranging from 0 to 1. <x≤0.1。 3. The vacancy-filled Hessler thermoelectric material according to claim 2, characterized in that, In the chemical formula, x = 0.02, 0.06, 0.

1.

4. The vacancy-filled Hessler thermoelectric material according to claim 3, characterized in that, The vacancy-filled Hessler thermoelectric material has an electrical conductivity between 85,000 and 365,000 S / m, a Seebeck coefficient between 94 and 220 μV / K, and a power factor between 33.6 and 44.5 μW / (cm·K). 2 The thermal conductivity is between 3.47 and 7.15 W / (m·K), and the zT value is between 0.15 and 1.

21.

5. The vacancy-filled Hessler thermoelectric material according to claim 4, characterized in that, In the chemical formula, x = 0.1, and the power factor is 43.2 μW / (cm·K) at 973 K. 2 The thermal conductivity is 3.47 W / (m·K), and the zT is 1.

21.

6. A method for preparing a vacancy-filled Hessler thermoelectric material as described in any one of claims 1-5, characterized in that, Using elemental Nb, Ti, Fe, Cr, and Sb particles as raw materials, a vacancy-filled Hessler thermoelectric material was prepared by high-energy ball milling and spark plasma sintering, followed by annealing at 900–1000 K for 6–8 days. The chemical formula of this material is: Nb 0.75 Ti 0.25 FeCr x Sb, where x takes values ​​ranging from 0 to 1. <x≤0.1。 7. The method for preparing a vacancy-filled Hessler thermoelectric material according to claim 6, characterized in that, The specific steps for preparing the vacancy-filled Hessler thermoelectric material are as follows: S1. Calculation: Based on the stoichiometric ratio of Nb:Ti:Fe:Cr:Sb = 0.75:0.25:1:x:1, calculate the mass of each element corresponding to a specific x value. S2. Sample preparation: Weigh the elemental Nb flakes, Ti flakes, Fe flakes, Cr particles, and Sb particles according to the mass calculated in step S1, and place the weighed raw materials in a stainless steel ball mill jar. S3, Alloying: The ball mill jar from step S2 is placed in a high-energy ball mill and subjected to continuous ball milling and material collision for a long time to obtain mixed powder; S4. Sintering: Weigh a certain amount of the mixed powder obtained in step S3 into a graphite mold, then place the mold into a spark plasma sintering equipment, evacuate it and apply a certain pressure to start sintering, and finally hold it at a certain temperature for a period of time, then release the pressure and let it cool naturally to room temperature to obtain a preliminary sample. S5. Annealing: The preliminary sample obtained by sintering in step S4 is annealed at high temperature to obtain vacancy-filled Hessler thermoelectric material.

8. The method for preparing a vacancy-filled Hessler thermoelectric material according to claim 7, characterized in that, In step S2, in an argon glove box, the elemental Nb flakes, Ti flakes, Fe flakes, Cr particles, and Sb particles are weighed according to the mass calculated in step S1. In step S3, the ball milling time is set to 20-30 hours; In step S4, the sintering gas pressure is 58-62MPa, the applied pressure is 6-6.5kN, the temperature is raised to 900℃ at a sintering rate of 30-50℃ / min, and the holding time is 10-15min. In step S5, the annealing temperature is 973K and the annealing time is 7 days.

Images