Defect state semi-heusler thermoelectric material, preparation method and application

Abstract

The application discloses a defect-state half-Heusler thermoelectric material, a preparation method and application, and relates to the technical field of thermoelectric materials. The problems of high intrinsic lattice thermal conductivity of the existing half-Heusler thermoelectric material and the limitation of the preparation process of the conventional melting method due to the difference in melting points of component elements are solved. The material is a half-Heusler thermoelectric material composed of non-stoichiometric Zr, Ni and Bi elements and having intrinsic vacancy defects in the crystal structure, and the chemical formula is Zr 0.88 NiBi. A preparation method of the defect-state half-Heusler thermoelectric material is also provided. Zr, Ni and Bi elements are taken in a preset proportion, high-energy ball milling is used to ball mill raw materials, and mixed powder without block condensation is obtained; a hot-pressing sintering process is used to solidify the mixed powder to obtain a hot-pressing sintering sample; high-temperature annealing is performed on the hot-pressing sintering sample, and the sample is cooled to room temperature to obtain a finished product. The half-Heusler material has low lattice thermal conductivity and excellent performance.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric materials technology, and in particular to a defect-state semi-Houseler thermoelectric material, its preparation method, and its application. Background Technology

[0002] Thermoelectric power generation technology can directly convert low-quality waste heat into high-quality electrical energy, offering advantages such as zero emissions, no noise, and no moving mechanical parts, making it a next-generation green energy technology. Semi-Heusler compounds, due to their unique properties, have become star materials in the field of thermoelectric power generation.

[0003] However, the main drawback of traditional semi-Høesler compounds as thermoelectric materials lies in their intrinsically high lattice thermal conductivity. While introducing heteroatoms is a common method to reduce lattice thermal conductivity, this approach suffers from limited reduction due to the solubility limit of these heteroatoms, resulting in conductivity still significantly higher than that of other classic thermoelectric materials (such as Bi₂Te₃ and PbTe). Therefore, to further explore the thermoelectric properties of semi-Høesler compounds and fully realize their power generation potential, directly developing novel semi-Høesler compounds with intrinsically low lattice thermal conductivity is a crucial development path. Simultaneously, conventional melt-processing methods struggle to precisely control component content when there are significant differences in the melting points of the constituent elements, directly hindering the development of new materials. Summary of the Invention

[0004] The purpose of this invention is to address the problems of high intrinsic lattice thermal conductivity in existing semi-Høesler thermoelectric materials and the limitations of conventional melting methods due to differences in the melting points of constituent elements. A novel defect-state semi-Høesler compound with the chemical formula Zr is prepared through a high-energy ball milling, hot-pressing sintering, and high-temperature annealing process. 0.88 NiBi has a lattice thermal conductivity of only 1.4 W / (m·K) at room temperature, which is the lowest experimental value for a semi-Heusler material system to date.

[0005] To achieve the above objectives, the present invention specifically adopts the following technical solution:

[0006] A defect-state semi-Heusler thermoelectric material is a semi-Heusler thermoelectric material composed of non-stoichiometric Zr, Ni, and Bi elements and possessing intrinsic vacancy defects in its crystal structure. Its chemical formula is Zr. 0.88 NiBi.

[0007] This invention also provides a method for preparing a defect-state semi-Houseler thermoelectric material, comprising the following steps:

[0008] S1. Take Zr, Ni and Bi elements according to the preset ratio, and use high-energy ball milling to ball mill the raw materials to obtain a mixed powder without blocky agglomeration;

[0009] S2. The mixed powder is solidified using a hot-pressing sintering process to obtain a hot-pressed sintered sample;

[0010] S3. The hot-pressed sintered sample is annealed at high temperature and then cooled to room temperature to obtain the finished material.

[0011] Furthermore, ball milling was carried out under an argon inert atmosphere.

[0012] Furthermore, in S1, the ball milling time is 20-30 hours, and the mass ratio of balls to raw materials is 1.33-1.66.

[0013] Furthermore, in S2, the heating rate is 100-200℃ / min, the hot pressing temperature is 700-750℃, and the pressure is 70-80MPa.

[0014] Furthermore, the duration of the S2 hot pressing sintering is 2-5 minutes.

[0015] Furthermore, in S3, the heating rate is 3-4℃ / min, and the annealing temperature is 700-750℃.

[0016] Furthermore, the duration of the S3 high-temperature annealing is 40-50 hours.

[0017] This invention also provides an application of a defect-state semi-Houseler thermoelectric material.

[0018] Compared with the prior art, the advantages of the present invention are as follows:

[0019] 1. The present invention provides a defect-state semi-Heusler thermoelectric material composed of non-stoichiometric Zr, Ni, and Bi elements. The inventors discovered that controlling the generation of vacancy defects in Ni and Bi was ineffective. Therefore, by adjusting the vacancy defects in Zr, a material with the chemical formula Zr was obtained. 0.88 Characterization of NiBi revealed that this semi-Heusler thermoelectric material possesses intrinsic vacancy defects in its crystal structure. Furthermore, its lattice thermal conductivity was measured to be as low as 1.4 W / (m·K) at room temperature, which is the lowest experimental value for semi-Heusler material systems to date.

[0020] 2. The present invention provides a method for preparing a defect-state semi-Houseler thermoelectric material, which employs a high-energy ball milling method to directly combine Zr, Ni, and Bi elements, ultimately obtaining a uniform powder without blocky agglomeration. A hot-pressing sintering process is used to achieve rapid solidification of the ball-milled powder. The hot-pressed sintered sample undergoes high-temperature annealing, and the process parameters at each stage are adjusted to ensure that the prepared material has a stable thermodynamic structure and a lattice thermal conductivity as low as 1.4 W / (m·K) at room temperature, exhibiting excellent performance. Furthermore, the preparation method is simple, easy to operate, and readily applicable for widespread application.

[0021] 3. The application of the defect-state semi-Houseler thermoelectric material provided by this invention has broad applicability and promising application prospects. Attached image description:

[0022] Figure 1 The X-ray diffraction patterns are those of the semi-Houseler thermoelectric material 2 in Example 2 of the present invention and the comparative sample 1 in Comparative Example 1.

[0023] Figure 2 This is a comparative analysis diagram of the lattice thermal conductivity of the semi-Heuschler thermoelectric material in Example 2 of the present invention and the conventional semi-Heuschler thermoelectric material.

[0024] Figure 1 The vertical axis represents intensity.

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0026] Therefore, the following detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Detailed Implementation

[0027] A defect-state semi-Heusler thermoelectric material is a semi-Heusler thermoelectric material composed of non-stoichiometric Zr, Ni, and Bi elements and possessing intrinsic vacancy defects in its crystal structure. Its chemical formula is Zr. 0.88 NiBi.

[0028] The specific process for adjusting defect types is as follows:

[0029] Based on the number of outer electrons of Zr, Ni, and Bi, ZrNiBi conforms to stoichiometry:

[0030] Valence electron number = 4(Zr 5s) 2 4d 2 )+10(Ni 4s 2 3D 8 )+5(Bi 6s 2 6p 3 ) = 19

[0031] Net valence electrons = 4 (Zr 4+ 5s 0 4d 0 )-0(Ni 0 3D10 )-3(Bi 3- 6s 2 6p 6 ) = 1

[0032] At this point, it is a non-thermodynamically stable structure. From an energy perspective, and considering the 18-electron rule, a decrease in the number of net valence electrons is conducive to the emergence of a stable structure.

[0033] Regulation of Zr:

[0034] Valence electron number = 3 (0.75Zr 5s) 2 4d 2 )+10(Ni 4s 2 3D 8 )+5(Bi 6s 2 6p 3 ) = 18

[0035] Net valence electron count = 3 (0.75Zr) 4+ 5s 0 4d 0 )-0(Ni 0 3D 10 )-3(Bi 3- 6s 2 6p 6 ) = 0

[0036] Regulation of Ni:

[0037] Valence electron number = 4(Zr 5s) 2 4d 2 )+9(0.9Ni 4s 2 3D 8 )+5(Bi 6s 2 6p 3 ) = 18

[0038] Net valence electrons = 4 (Zr 4+ 5s 0 4d 0 )-0(0.9Ni 0 3D 10 )-3(Bi 3- 6s 2 6p 6 ) = 1

[0039] Regulation of Bi:

[0040] Valence electron number = 4(Zr 5s) 2 4d 2 )+10(Ni 4s 2 3D 8 )+4(0.8Bi 6s 26p 3 ) = 18

[0041] Net valence electrons = 4 (Zr 4+ 5s 0 4d 0 )-0(Ni 0 3D 10 )–2.4(0.8Bi 3- 6s 2 6p 6 ) = 1.6

[0042] Therefore, manipulation of Ni and Bi is ineffective. Thus, the defect state described in this invention is a Zr vacancy defect.

[0043] It is understood that the defect-state semi-Heusler thermoelectric material provided by this invention is composed of Zr, Ni, and Bi elements in a non-stoichiometric ratio. Furthermore, the inventors discovered that controlling the generation of vacancy defects in Ni and Bi was ineffective. Therefore, by adjusting the vacancy defects in Zr, they obtained a material with the chemical formula Zr... 0.88 Characterization of NiBi revealed that this semi-Heuschler thermoelectric material possesses intrinsic vacancy defects in its crystal structure. Furthermore, its lattice thermal conductivity at room temperature was measured to be as low as 1.4 W / (m·K), the lowest experimental value for a semi-Heuschler material system to date. Therefore, the defect-state semi-Heuschler thermoelectric material provided by this invention exhibits superior performance.

[0044] This invention also provides a method for preparing a defect-state semi-Houseler thermoelectric material, comprising the following steps:

[0045] S1. Take Zr, Ni and Bi elements according to the preset ratio, and use high-energy ball milling to ball mill the raw materials to obtain a mixed powder without blocky agglomeration;

[0046] S2. The mixed powder is solidified using a hot-pressing sintering process to obtain a hot-pressed sintered sample;

[0047] S3. The hot-pressed sintered sample is annealed at high temperature and then cooled to room temperature to obtain the finished material.

[0048] It is understandable that Zr and Ni have melting points of 1855℃ and 1455℃, respectively, while Bi has a melting point of only 271℃. Since the commonly used melting method for semi-Heusler thermoelectric materials requires melting all three elements, and the melting points of the three components in this invention differ significantly, the currently used melting method struggles to achieve precise control of the component content, severely impacting the development of thermodynamically stable defect-state structures.

[0049] Furthermore, this invention abandons the melting method and employs a high-energy ball milling method to directly combine Zr, Ni, and Bi elements, without considering the differences in melting points among the three elements, ultimately obtaining a uniform powder without lumps or agglomeration. Next, a hot-pressing sintering process is used to achieve rapid solidification of the ball-milled powder. The combination of uniform mixing from high-energy ball milling and rapid hot-pressing sintering allows for precise control of the composition of the prepared material. Finally, the hot-pressed sintered sample undergoes high-temperature annealing, which further enhances the internal structure of the material. Precise adjustment of process parameters at each stage ensures the thermodynamic stability of the prepared material. The lattice thermal conductivity of the finished material is as low as 1.4 W / (m·K) at room temperature, exhibiting excellent performance. Moreover, the preparation method is simple, easy to operate, and readily applicable for widespread application.

[0050] In some embodiments of the present invention, the preset ratio is Zr:Ni:Bi = 0.88:1:1.

[0051] In some embodiments of the present invention, ball milling is performed under an argon inert atmosphere.

[0052] In some embodiments of the present invention, the ball milling time in S1 is 20-30 hours, and the mass ratio of balls to raw materials is 1.33-1.66.

[0053] In some embodiments of the present invention, the heating rate in S2 is 100-200°C / min, the hot pressing temperature is 700-750°C, and the pressure is 70-80 MPa.

[0054] In some embodiments of the present invention, the duration of the S2 hot pressing sintering is 2-5 minutes.

[0055] In some embodiments of the present invention, the heating rate in step S3 is 3-4°C / min, and the annealing temperature is 700-750°C.

[0056] In some embodiments of the present invention, the duration of the S3 high-temperature annealing is 40-50 hours.

[0057] In some embodiments of the present invention, S3 is operated in a vacuum environment.

[0058] This invention also provides an application of a defect-state semi-Houseler thermoelectric material. It has broad applicability and promising application prospects.

[0059] Example 1

[0060] This embodiment provides a defect-state semi-Heusler thermoelectric material 1, which is a semi-Heusler thermoelectric material composed of non-stoichiometric Zr, Ni, and Bi elements and has intrinsic vacancy defects in its crystal structure. Its chemical formula is Zr 0.88 NiBi.

[0061] Example 2

[0062] In this embodiment, a method for preparing a defect-state semi-Heusler thermoelectric material is provided, comprising the following steps:

[0063] S1. Take Zr, Ni and Bi elements according to the preset ratio, and ball mill the raw materials using high-energy ball milling under an argon inert atmosphere to obtain a mixed powder without lumps; ball mill for 20 hours, and the mass ratio of balls to raw materials is 1.64.

[0064] S2. The mixed powder is solidified by hot pressing sintering process to obtain hot pressing sintered sample. The heating rate is 150℃ / min, the hot pressing temperature is 730℃, the pressure is 70-80MPa, and the hot pressing sintering time is 2 minutes.

[0065] S3. The hot-pressed sintered sample was subjected to high-temperature annealing in a vacuum environment with a heating rate of 3.8℃ / min, an annealing temperature of 700℃, and a high-temperature annealing time of 40 hours. After cooling to room temperature, the finished semi-Household thermoelectric material 2 was obtained.

[0066] Comparative Example 1

[0067] Comparative Example 1 provides a semi-Heuschler thermoelectric material comparative sample 1, which is a semi-Heuschler thermoelectric material composed of Zr, Ni and Bi elements in stoichiometric ratios, with the chemical formula ZrNiBi.

[0068] Experimental Example 1

[0069] 1.1 Test Setup

[0070] The semi-Houselle thermoelectric material 2 from Example 2 of this invention and the comparative sample 1 from Comparative Example 1 were selected and subjected to spectral analysis. Their X-ray diffraction patterns are shown below. Figure 1 .

[0071] 1.2 Results Analysis

[0072] Please refer to this document. Figure 1 By comparing the semi-Heusler thermoelectric material 2 of Example 2 with the comparative sample 1 of Comparative Example 1, the diffraction patterns of the stoichiometric ZrNiBi material show a large number of impurity peaks, indicating a non-thermodynamically stable structure. Furthermore, the defective Zr in Example 2... 0.88 NiBi exhibits no impurity peaks in its diffraction pattern. The relevant diffraction peaks correspond to the (111), (200), (220), (311), (222), (400), (331), (420), and (422) crystal planes, respectively, with the space group being [missing information]. Consistent with traditional semi-Høisler compounds, this enriches the semi-Høisler material system.

[0073] Experiment Example 2

[0074] 2.1 Test Setup

[0075] The lattice thermal conductivity of the semi-Heuschler thermoelectric material 2 involved in Embodiment 2 of the present invention and the conventional semi-Heuschler thermoelectric material were analyzed respectively. The results of the lattice thermal conductivity analysis are shown in […]. Figure 2 .

[0076] 2.2 Results Analysis

[0077] Please refer to this document. Figure 2 By comparing the semi-Heuschler thermoelectric material 2 of the present invention with that of a conventional semi-Heuschler thermoelectric material, the semi-Heuschler thermoelectric material 2 of the present invention: Zr 0.88 The lattice thermal conductivity of NiBi is only 1.4 W / (m·K), which is significantly lower than that of traditional semi-Heusler thermoelectric materials, and can be reduced by up to an order of magnitude. At the same time, its lattice thermal conductivity is comparable to that of two classic thermoelectric materials (PbTe and Bi2Te3), effectively avoiding the drawbacks of the intrinsically high lattice thermal conductivity of the semi-Heusler system.

[0078] The above embodiments are merely one implementation of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A defect-state semi-Houseler thermoelectric material, characterized in that, It is a semi-Houseler thermoelectric material composed of non-stoichiometric Zr, Ni, and Bi elements and possessing intrinsic vacancy defects in its crystal structure. Its chemical formula is Zr. 0.88 NiBi.

2. The method for preparing a defect-state semi-Heusler thermoelectric material according to claim 1, characterized in that, Includes the following steps: S1. Take Zr, Ni and Bi elements according to the preset ratio, and use high-energy ball milling to ball mill the raw materials to obtain a mixed powder without blocky agglomeration; S2. The mixed powder is solidified using a hot-pressing sintering process to obtain a hot-pressed sintered sample; S3. The hot-pressed sintered sample is annealed at high temperature and then cooled to room temperature to obtain the finished material.

3. The defect-state semi-Heusler thermoelectric material according to claim 2, characterized in that, Ball milling was performed under an inert argon atmosphere.

4. The defect-state semi-Heusler thermoelectric material according to claim 3, characterized in that, The ball milling time in S1 is 20-30 hours, and the mass ratio of balls to raw materials is 1.33-1.

66.

5. The defect-state semi-Heusler thermoelectric material according to claim 2, characterized in that, The heating rate in S2 is 100-200℃ / min, the hot pressing temperature is 700-750℃, and the pressure is 70-80MPa.

6. The defect-state semi-Heusler thermoelectric material according to claim 5, characterized in that, The duration of the S2 hot pressing sintering is 2-5 minutes.

7. The defect-state semi-Heusler thermoelectric material according to claim 2, characterized in that, The heating rate in S3 is 3-4℃ / min, and the annealing temperature is 700-750℃.

8. The defect-state semi-Heusler thermoelectric material according to claim 7, characterized in that, The S3 high-temperature annealing time is 40-50 hours.

9. The application of the defect-state semi-Houseler thermoelectric material as described in claim 1.

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