Ho-doped Mg3SbBi-based thermoelectric material and preparation method and application thereof

Abstract

The invention relates to the technical field of new energy materials, in particular to a Ho-doped Mg3SbBi-based thermoelectric material and a preparation method and application thereof. The chemical formula of the Ho-doped Mg3SbBi-based thermoelectric material is Mg < 3.08-x > SbBiHox, wherein x is greater than or equal to 0 and less than or equal to 0.08. The invention also provides a preparation method of the Ho-doped Mg3SbBi-based thermoelectric material, which comprises the following steps: sealing solid elementary substances of magnesium, antimony, bismuth and holmium in a tantalum tube or a stainless steel crucible, and melting the solid elementary substances in vacuum to form a cast ingot; grinding the cast ingot to obtain alloy particles; and carrying out spark plasma sintering on the particles to obtain the Ho-doped Mg3SbBi-based thermoelectric material. The invention further provides application of the Ho-doped Mg3SbBi-based thermoelectric material as a heat energy and electric energy conversion material. According to the invention, the synthesis problem of low conductivity caused by near-room-temperature grain boundary scattering of the existing Mg3 (Sb, Bi) 2-based thermoelectric material is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy materials, in particular to a Ho-doped Mg3SbBi-based thermoelectric material and a preparation method and application thereof. BACKGROUND

[0002] Thermoelectric technology, as an advanced technology that can realize the direct conversion between heat and electricity, has key application value in many fields such as industrial waste heat recovery and solid-state refrigeration. This technology not only can effectively improve energy utilization efficiency, but also has important significance for responding to the global demand for energy efficiency improvement. The energy conversion efficiency of thermoelectric materials is determined by a dimensionless thermoelectric figure of merit zT, whose calculation formula is zT= S 2 σT / κ, where S represents the Seebeck coefficient, σ represents the electrical conductivity, κ represents the thermal conductivity, and T represents the absolute temperature. In order to achieve excellent thermoelectric performance, the material needs to have high electrical transport performance (S 2 σ) and low thermal conductivity (κ). However, there is an inherent coupling relationship between these two parameters, that is, while improving the carrier concentration to increase the electrical conductivity, the Seebeck coefficient will often decrease, and it is difficult to simultaneously reduce the thermal conductivity, which is a core bottleneck restricting the performance improvement of thermoelectric materials.

[0003] In the past few decades, the scientific research community has developed a variety of thermoelectric material systems, including Bi2Te3, PbTe, Mg2Si, SnSe, SiGe, and half-Heusler compounds. However, these material systems have obvious limitations. For example, the n-type performance of Bi2Te3 is much lower than its p-type performance, and p-type GeTe-based materials lack matching high-performance n-type complementary material systems. In addition, the components of some materials are scarce in resources, which does not meet the green and sustainable demand. Therefore, developing high-performance n-type thermoelectric materials based on abundant elements on earth has become a key direction to promote the industrialization of thermoelectric technology.

[0004] Mg3(Sb, Bi)2-based thermoelectric materials have gradually become a research hotspot due to their abundant element reserves, low cost, and intrinsic low lattice thermal conductivity, high power factor caused by high-energy valley degeneracy of conduction band, etc. However, the electrical conductivity of Mg3(Sb, Bi)2-based thermoelectric materials is low, especially the grain boundary scattering of carriers at near room temperature, which limits the improvement of the dimensionless zT value. Therefore, how to effectively improve the electrical conductivity of Mg3(Sb, Bi)2-based thermoelectric materials while maintaining low lattice thermal conductivity is a major challenge and the key to breaking through the existing thermoelectric performance. SUMMARY

[0005] Therefore, the present application aims to provide a Ho-doped Mg3SbBi-based thermoelectric material and a preparation method and application thereof, so as to solve the problem of low electrical conductivity caused by near room temperature grain boundary scattering of the existing Mg3(Sb, Bi)2-based thermoelectric material.

[0006] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: A Ho-doped Mg3SbBi-based thermoelectric material, the chemical formula of the Ho-doped Mg3SbBi-based thermoelectric material is Mg 3.08-x SbBiHo x , wherein the value range of x is 0 ≤ x ≤ 0.08.

[0007] According to the above technical means, by doping Ho in Mg3SbBi, since there is a small electronegativity difference between Ho and the host element Mg, the defect formation energy is lower, thereby effectively improving the carrier concentration, which can be as high as 7.2 × 10 19 cm -3 . And the sample prepared by the tantalum tube sealing melting technology used in the present application has a higher carrier mobility, which can be as high as 128 cm 2 V -1 s -1 , which significantly improves the electrical conductivity of the Mg3SbBi thermoelectric material, effectively solving the problem of low electrical conductivity caused by near room temperature grain boundary scattering in the existing preparation of Mg3(Sb, Bi)2-based thermoelectric material. At the same time, the doping ratio of Ho is ingeniously controlled, the doping of Ho produces a large mass field fluctuation, enhances the point defect scattering, and further reduces the lattice thermal conductivity, which can be as low as 0.49 W m -1 K -1 . Therefore, through the synergistic effect of carrier concentration and lattice thermal conductivity, the thermoelectric performance of the material is significantly improved.

[0008] Among them, there have been more reports focusing on doping chalcogen elements at the anion Sb position, but the low doping efficiency leads to low carrier concentration. In the present application, the electronegativity of Mg element is 1.31, and the electronegativity of Ho element is 1.23. Therefore, by doping the Ho element with small electronegativity difference in the Mg site, the defect formation energy of Ho as a donor impurity can be reduced, thereby improving the carrier concentration and effectively breaking through the bottleneck of difficult to obtain high carrier concentration of chalcogen elements. In addition, the large mass difference between Ho element (relative atomic mass 164.9) and Mg element (relative atomic mass 24.31) introduces strong mass field fluctuation. The fluctuation can enhance the scattering of phonons by point defects, significantly reduce the lattice thermal conductivity of the material, and finally realize the effective decoupling of the electroacoustic transport parameters, greatly improve the thermoelectric performance of the matrix material.

[0009] Preferably, the Ho-doped Mg3SbBi-based thermoelectric material is an n-type thermoelectric material.

[0010] Preferably, the value of x is 0.01, 0.03, 0.05, 0.07 or 0.08.

[0011] This invention also provides a method for preparing Ho-doped Mg3SbBi-based thermoelectric materials, comprising the following steps: S1. Solid elements of magnesium (Mg), antimony (Sb), bismuth (Bi) and holmium (Ho) are sealed in a tantalum tube crucible and melted into an ingot under vacuum. S2. Grind the ingot to obtain alloy particles; S3. The particles are subjected to discharge plasma sintering to obtain Ho-doped Mg3SbBi-based thermoelectric materials, i.e., Mg 3.08- x SbBiHo x Thermoelectric materials.

[0012] Based on the aforementioned technical methods, firstly, by completely melting each solid element at high temperature, uniform mixing between elements is effectively achieved, thus ensuring the homogeneity of the alloy composition. Simultaneously, the melting process promotes internal chemical reactions within the material, contributing to the formation of the desired compounds or phase structures. The prolonged melting combined with a slow cooling process facilitates the formation of sufficiently large grain sizes. Secondly, by subjecting the particles to spark plasma sintering (SPS) heat treatment at lower temperatures, diffusion and adhesion between particles are effectively enhanced, reducing the material's porosity and optimizing its microstructure, such as grain size and shape, thereby increasing density and mechanical strength, resulting in a dense solid material. Simultaneously, the electrical and thermal conductivity of the thermoelectric material is optimized and controlled. Therefore, through the synergistic effect of melting and sintering, multiple optimizations of material homogeneity, density, and large grain size are achieved, making Mg... 3.08-x SbBiHo x The thermoelectric properties of the material have been significantly improved.

[0013] Among these advantages, Ho doping offers at least the following benefits: 1) The lower electronegativity difference between Ho and the host element Mg helps improve doping efficiency, allowing for a more effective increase in carrier concentration, thereby contributing to improved conductivity (σ). 2) The larger mass difference between Ho and the host element helps enhance point defect scattering and suppress phonon propagation, resulting in lower thermal conductivity (κ). In summary, the method for preparing Ho-doped Mg3SbBi-based thermoelectric materials not only improves the thermoelectric performance of the materials but also brings additional environmental and economic advantages, contributing to the commercialization and sustainable development of thermoelectric technology.

[0014] Preferably, in the S1, the temperature is raised from room temperature to 1273-1423 K in 10-12 h. The lower heating rate can ensure the sufficient melting and reaction of the raw materials, and can inhibit the volatilization of Mg element and the ordered growth of larger grains. The melting is performed at a temperature of 1273-1423 K for 20-24 h, and the cooling mode of melting is furnace cooling to room temperature.

[0015] Preferably, in the S1, the temperature is raised from room temperature to 1373 K in 11 h, the melting is performed at a temperature of 1373 K for 24 h, and the cooling mode of melting is furnace cooling to room temperature.

[0016] Preferably, in the S1, the grain size of the sample prepared by the melting method is larger than that of the sample prepared by the ball milling method, which is beneficial to alleviate the near-room-temperature grain boundary scattering, thereby obtaining high electrical conductivity. Therefore, the ingot is prepared by vacuum sealing and melting in a tantalum tube, the vacuum degree of the sealed tantalum tube is 10 -1 Pa.

[0017] Preferably, in the S3, the temperature of the spark plasma sintering is 893-923 K, the pressure is 45-55 Mpa, and the sintering time is 2-3 min.

[0018] Preferably, in the S3, the temperature of the spark plasma sintering is 923 K, the pressure is 50 Mpa, and the sintering time is 2.5 min.

[0019] Preferably, in the S2, the ingot grinding is performed manually in a glove box by using a agate mortar.

[0020] By manually grinding in a glove box by using a agate mortar, the purity of the alloy particles is ensured, and the oxygen content of the alloy particles can be effectively reduced, which is beneficial to obtain lower thermal conductivity.

[0021] Preferably, in the S2, after the ingot grinding, the alloy particles are sieved to have a particle size of 1-2 mm.

[0022] Preferably, in the S2, after the ingot grinding, the alloy particles are sieved to have a particle size of 1 mm.

[0023] Preferably, the magnesium (Mg) is selected from magnesium (Mg) particles, and the purity of the magnesium (Mg) particles is 99.5 wt%-99.95 wt%.

[0024] Preferably, the antimony (Sb) is selected from antimony (Sb) particles, and the purity of the antimony (Sb) particles is 99.99 wt%-99.999 wt%.

[0025] Preferably, the bismuth (Bi) is selected from bismuth (Bi) particles with a purity of 99.99 wt% to 99.999 wt%.

[0026] Preferably, the holmium (Ho) is selected from holmium (Ho) blocks with a purity of 99.9 wt% to 99.999 wt%.

[0027] The application also provides an application of the Ho-doped Mg3SbBi-based thermoelectric material as a heat energy and electric energy conversion material.

[0028] The application has the following beneficial effects: The Ho-doped Mg3SbBi-based thermoelectric material has the following advantages: first, the carrier concentration is significantly improved by Ho doping, and the highest carrier concentration can reach 7.2 × 10 19 cm -3 , which is 2 orders of magnitude higher than that of the substrate. 2 V -1 s -1 , which is 2-3 times that of the traditional ball milling preparation method.

[0029] The Ho-doped Mg3SbBi-based thermoelectric material has the following advantages: first, the carrier concentration is significantly improved by Ho doping, and the highest carrier concentration can reach 7.2 × 10 19 cm -3 , which is 2 orders of magnitude higher than that of the substrate. 2 V -1 s -1 , which is 2-3 times that of the traditional ball milling preparation method.

[0030] The preparation method of the Ho-doped Mg3SbBi-based thermoelectric material has the following advantages: first, the complete melting of the solid elements at high temperature effectively realizes the uniform mixing of the elements, thereby ensuring the uniformity of the alloy composition. The melting method also promotes the full reaction inside the material, which is conducive to the ordered growth of large-grain materials. At the same time, the particles are subjected to discharge plasma sintering heat treatment at a lower temperature, which reduces the possibility of Mg evaporation and effectively improves the diffusion and adhesion between the particles, reduces the porosity of the material, and optimizes the microstructure of the material, such as grain size and shape, improves the density and mechanical strength, thereby forming a dense solid material, and also realizes the optimization and control of the electrical conductivity and thermal conductivity of the thermoelectric material. In the field of new energy material technology, it has the value of popularization and application. Attached Figure Description

[0031] Figure 1 Mg 3.08-x SbBiHo x XRD diffraction patterns of powder samples at room temperature, x = 0~0.08; Figure 2 SEM images of samples with x = 0.05 and 0.07; Figure 3 Mg 3.08-x SbBiHo x Carrier concentration plot at room temperature for samples with x = 0~0.08; Figure 4 Mg 3.08-x SbBiHo x Carrier mobility plot at room temperature for samples with x = 0~0.08; Figure 5 Mg 3.08-x SbBiHo x Conductivity graph of samples with x = 0~0.08 as a function of temperature; Figure 6 Mg 3.08-x SbBiHo x Seebeck coefficient plot of samples with x = 0~0.08 as a function of temperature; Figure 7 Mg 3.08-x SbBiHo x Power factor plot of samples with x = 0~0.08 as a function of temperature; Figure 8 Mg 3.08-x SbBiHo x , Lattice thermal conductivity diagram of samples with x = 0~0.08 as a function of temperature; Figure 9 Mg 3.08-x SbBiHo x Thermoelectric figure of merit zT of the sample with x = 0~0.08 as a function of temperature. Detailed Implementation

[0032] The following description, with reference to preferred embodiments, illustrates the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are merely illustrative of the present invention and not intended to limit the scope of protection of the present invention.

[0033] The purity of the magnesium (Mg) column used in the following examples and comparative examples is 99.5 wt% to 99.95 wt%, the purity of the antimony (Sb) pill is 99.99 wt% to 99.999 wt%, the purity of the bismuth (Bi) particle is 99.99 wt% to 99.999 wt%, and the purity of the holmium (Ho) block is 99.9 wt% to 99.999 wt%.

[0034] Example 1 A preparation method of a Ho-doped Mg3SbBi-based thermoelectric material, comprising the following steps: S1, weighing solid elemental raw materials of magnesium (Mg) column, antimony (Sb) pill, bismuth (Bi) particle and holmium (Ho) block according to a stoichiometric ratio of 3.07:1:1:0.01, then loading into a tantalum tube crucible, sealing with a micro smelting furnace, and then placing into a quartz tube, and then sealing the quartz tube with a vacuum sealing machine, and the vacuum degree is 10 -1 Pa; S2, placing the sealed quartz tube in S1 into a box furnace, slowly heating for 10 h to make the temperature rise from room temperature to 1273 K, and keeping the temperature at 1273 K for 24 h, and then slowly cooling to room temperature with the furnace, and obtaining an ingot; S3, grinding the ingot obtained in S2 manually with a agate mortar in an argon-filled glove box, and sieving to obtain alloy particles with a particle size of 1 mm; S4, loading the alloy particles obtained in S3 into a graphite mold, and densifying and sintering for 2.5 min at a temperature of 923 K and a pressure of 50 Mpa with a plasma sintering system (SPS), and testing the density of the sintered material by the Archimedes drainage method, and obtaining a bulk thermoelectric material Mg 3.07 SbBiHo 0.01 , that is, a Ho-doped Mg3SbBi-based thermoelectric material.

[0035] Example 2 A preparation method of a Ho-doped Mg3SbBi-based thermoelectric material, comprising the following steps: S1, weighing solid elemental raw materials of magnesium (Mg) column, antimony (Sb) pill, bismuth (Bi) particle and holmium (Ho) block according to a stoichiometric ratio of 3.05:1:1:0.03, then loading into a tantalum tube crucible, sealing with a micro smelting furnace, and then placing into a quartz tube, and then sealing the quartz tube with a vacuum sealing machine, and the vacuum degree is 10 -1 Pa; S2, placing the sealed quartz tube in S1 into a box furnace, slowly heating for 10 h to make the temperature rise from room temperature to 1273 K, and keeping the temperature at 1273 K for 24 h, and then slowly cooling to room temperature with the furnace, and obtaining an ingot; S3, the ingot obtained in S2 is ground manually in a marver mortar and sieved to obtain alloy particles with a particle size of 1 mm in an argon-filled glove box; S4, the alloy particles obtained in S3 are loaded into a graphite mold, and densification sintering is performed at a temperature of 923 K and a pressure of 50 Mpa for 2.5 min using a plasma sintering system (SPS), and the density of the sintered material is tested by the Archimedes drainage method, to obtain a bulk thermoelectric material Mg 3.05 SbBiHo 0.03 , i.e. a Ho-doped Mg3SbBi-based thermoelectric material.

[0036] Example 3 A preparation method of a Ho-doped Mg3SbBi-based thermoelectric material, comprising the following steps: S1, solid elemental raw materials of magnesium (Mg) column, antimony (Sb) pill, bismuth (Bi) particle and holmium (Ho) block are weighed according to a stoichiometric ratio of 3.03:1:1:0.05, then loaded into a tantalum tube crucible, sealed by a micro smelting furnace, and then placed into a quartz tube, and then the quartz tube is sealed by a vacuum sealing machine, and the vacuum degree is 10 -1 Pa; S2, the sealed quartz tube in S1 is placed into a box furnace, heated slowly for 10 h to make the temperature rise from room temperature to 1273 K, and kept at 1273 K for 24 h, and then cooled slowly to room temperature with the furnace, to obtain an ingot; S3, the ingot obtained in S2 is ground manually in a marver mortar and sieved to obtain alloy particles with a particle size of 1 mm in an argon-filled glove box; S4, the alloy particles obtained in S3 are loaded into a graphite mold, and densification sintering is performed at a temperature of 923 K and a pressure of 50 Mpa for 2.5 min using a plasma sintering system (SPS), and the density of the sintered material is tested by the Archimedes drainage method, to obtain a bulk thermoelectric material Mg 3.03 SbBiHo 0.05 , i.e. a Ho-doped Mg3SbBi-based thermoelectric material.

[0037] Example 4 A preparation method of a Ho-doped Mg3SbBi-based thermoelectric material, comprising the following steps: S1, solid elemental raw materials of magnesium (Mg) column, antimony (Sb) pill, bismuth (Bi) particle and holmium (Ho) block are weighed according to a stoichiometric ratio of 3.03:1:1:0.05, then loaded into a tantalum tube crucible, sealed by a micro smelting furnace, and then placed into a quartz tube, and then the quartz tube is sealed by a vacuum sealing machine, and the vacuum degree is 10 -1 Pa; S2, the sealed quartz tube in S1 is put into a box furnace, slowly heated for 10 h to make the temperature rise from room temperature to 1273 K, and kept at 1273 K for 24 h, and then slowly cooled to room temperature with the furnace to obtain an ingot; S3, the ingot obtained in S2 is manually ground in a marver mortar in an argon-filled glove box, and sieved to obtain alloy particles with a particle size of 1 mm; S4, the alloy particles obtained in S3 are loaded into a graphite mold, and densified sintering is performed at a temperature of 923 K and a pressure of 50 Mpa for 2.5 min by using a plasma sintering system (SPS), and the density of the material after sintering is tested by using the Archimedes drainage method to obtain a bulk thermoelectric material Mg3SbBiHo 3.01 SbBiHo 0.07 , that is, a Ho-doped Mg3SbBi-based thermoelectric material.

[0038] Example 5 A preparation method of a Ho-doped Mg3SbBi-based thermoelectric material, comprising the following steps: S1, solid elemental raw materials magnesium (Mg) column, antimony (Sb) pill, bismuth (Bi) particle and holmium (Ho) block are weighed according to the stoichiometric ratio of 3:1:1:0.08, then loaded into a tantalum tube crucible, sealed by using a micro smelting furnace, and then put into a quartz tube, and then sealed by using a vacuum sealing machine, and the vacuum degree is 10 -1 Pa; S2, the sealed quartz tube in S1 is put into a box furnace, slowly heated for 10 h to make the temperature rise from room temperature to 1273 K, and kept at 1273 K for 24 h, and then slowly cooled to room temperature with the furnace to obtain an ingot; S3, the ingot obtained in S2 is manually ground in a marver mortar in an argon-filled glove box, and sieved to obtain alloy particles with a particle size of 1 mm; S4, the alloy particles obtained in S3 are loaded into a graphite mold, and densified sintering is performed at a temperature of 923 K and a pressure of 50 Mpa for 2.5 min by using a plasma sintering system (SPS), and the density of the material after sintering is tested by using the Archimedes drainage method to obtain a bulk thermoelectric material Mg3SbBiHo 0.08 , that is, a Ho-doped Mg3SbBi-based thermoelectric material.

[0039] Example 6 A preparation method of a Ho-doped Mg3SbBi-based thermoelectric material, comprising the following steps: S1, solid elemental raw materials of magnesium (Mg) column, antimony (Sb) pill, bismuth (Bi) particle and holmium (Ho) block are weighed according to the stoichiometric ratio of 3.01:1:1:0.07, then loaded into a tantalum tube crucible, sealed with a micro smelting furnace, and then put into a quartz tube, then the quartz tube is sealed with a vacuum sealing machine, and the vacuum degree is 10 -1 Pa; S2, the sealed quartz tube in S1 is put into a box furnace, slowly heated for 11 h to make the temperature rise from room temperature to 1373 K, and kept at 1373 K for 24 h, and then slowly cooled to room temperature with the furnace, to obtain an ingot; S3, the ingot obtained in S2 is manually ground in an argon-filled glove box with a agate mortar, and sieved to obtain alloy particles with a particle size of 1 mm; S4, the alloy particles obtained in S3 are loaded into a graphite mold, and densified sintering is carried out under the conditions of a temperature of 903 K and a pressure of 50 Mpa for 3 min by using a plasma sintering system (SPS), and the density of the sintered material is tested by using the Archimedes drainage method, to obtain a bulk thermoelectric material Mg 3.01 SbBiHo 0.07 -1, that is, a Ho-doped Mg3SbBi-based thermoelectric material.

[0040] Example 7 A preparation method of a Ho-doped Mg3SbBi-based thermoelectric material, comprising the following steps.

[0041] S1, solid elemental raw materials of magnesium (Mg) column, antimony (Sb) pill, bismuth (Bi) particle and holmium (Ho) block are weighed according to the stoichiometric ratio of 3.01:1:1:0.07, then loaded into a tantalum tube crucible, sealed with a micro smelting furnace, and then put into a quartz tube, then the quartz tube is sealed with a vacuum sealing machine, and the vacuum degree is 10 -1 Pa; S2, the sealed quartz tube in S1 is put into a box furnace, slowly heated for 11 h to make the temperature rise from room temperature to 1373 K, and kept at 1373 K for 24 h, and then slowly cooled to room temperature with the furnace, to obtain an ingot; S3, the ingot obtained in S2 is manually ground in an argon-filled glove box with a agate mortar, and sieved to obtain alloy particles with a particle size of 1 mm; S4, the alloy particles obtained in S3 are loaded into a graphite mold, and densified sintering is carried out under the conditions of a temperature of 903 K and a pressure of 50 Mpa for 3 min by using a plasma sintering system (SPS), and the density of the sintered material is tested by using the Archimedes drainage method, to obtain a bulk thermoelectric material Mg 3.01 SbBiHo 0.07-2, i.e. Ho-doped Mg3SbBi-based thermoelectric material.

[0042] Comparative Example 1 A preparation method of a Mg3SbBi thermoelectric material, comprising the following steps: S1, weighing solid elemental raw materials of magnesium (Mg) column, antimony (Sb) pill and bismuth (Bi) particle according to a stoichiometric ratio of 3.08:1:1, then loading into a tantalum tube crucible, sealing with a micro smelting furnace, and then sealing the quartz tube with a vacuum sealing machine, with a vacuum degree of 10 -1 Pa; S2, placing the sealed quartz tube in S1 into a box furnace, slowly heating for 10 h to make the temperature rise from room temperature to 1273 K, and keeping the temperature at 1273 K for 24 h, and then slowly cooling to room temperature with the furnace to obtain an ingot; S3, manually grinding the ingot obtained in S2 in an argon-filled glove box with a agate mortar, and sieving to obtain alloy particles with a particle size of 1 mm; S4, loading the alloy particles obtained in S3 into a graphite mold, and densifying sintering for 2.5 min at a temperature of 923 K and a pressure of 50 Mpa with a plasma sintering system (SPS) to obtain a bulk thermoelectric material Mg 3.08 SbBi, i.e. Mg3SbBi-based thermoelectric material.

[0043] Detection and analysis 1) XRD analysis X-ray diffraction analysis was performed on the powder samples of the Ho-doped Mg3SbBi-based thermoelectric materials prepared in Examples 1 to 5, and the Mg3SbBi-based thermoelectric material prepared in Comparative Example 1, using a Bruker D8 Advance diffractometer at room temperature. The results are shown in Figure 1 .

[0044] From the analysis in Figure 1 , it can be seen that all the diffraction peaks of the sample of Comparative Example 1 (i.e. x = 0) are consistent with the standard card, and there are no diffraction peaks of other impurities such as Mg or MgO. Since Mg3Bi2 is solid-solved in Mg3Sb2, the position of the diffraction peak is between the standard cards of the two. The samples of the Ho-doped Mg3SbBi-based thermoelectric materials prepared in Examples 1 to 5 are single-phase materials, and no diffraction peaks of Ho element or other impurity phases are detected, thereby proving the success of Ho doping, while the Mg3SbBi-based thermoelectric material prepared in Comparative Example 1.

[0045] 2) SEM analysis The powder samples of Ho-doped Mg3SbBi-based thermoelectric materials prepared in Example 3 and Example 4 were observed by scanning electron microscopy (SEM) using a field emission scanning electron microscope (instrument model FESEM, Tescan Mira3) to characterize their chemical composition, and energy dispersive x-ray spectroscopy (EDS) was used for EDS spectrum analysis, and the results are shown in Figure 2 .

[0046] From Figure 2 a, it can be seen that the Mg, Sb, Bi and Ho elements in the Ho-doped Mg3SbBi sample with x = 0.05 prepared in Example 3 are uniformly distributed, indicating that Ho has entered the crystal lattice of the matrix and plays the role of a donor impurity. From Figure 2 b, it can be seen that the Ho element in the Ho-doped Mg3SbBi sample with x = 0.07 prepared in Example 4 appears in an enrichment region, indicating that the doping limit of this element has been reached, and thus the effect of improving the carrier concentration and electrical conductivity decreases.

[0047] 3) Performance analysis The electrical conductivity, Seebeck coefficient and power factor of the Ho-doped Mg3SbBi-based thermoelectric materials prepared in Examples 1 to 5, and the Mg3SbBi-based thermoelectric material prepared in Comparative Example 1 were tested with respect to temperature change using a commercial ZEM-3 device.

[0048] The thermal conductivity was calculated by the formula κ = ρCD, where ρ represents the density of the sample, which was measured by the Archimedes drainage method; C represents the heat capacity of the material, which was calculated by the Du Long-Potier law; and D represents the thermal diffusion coefficient, which was tested by the laser thermal conductivity method using the LFA 457 device of the German NIST company. The Hall carrier concentration and mobility at room temperature were tested using the Van der Pauw method using the Lake Shore 8400 Series device. The results are shown in Figures 2 to 8 .

[0049] Figure 2 is a graph of the room temperature carrier concentration as a function of Ho content; Figure 3 is a graph of the room temperature carrier mobility as a function of Ho content. The electrical conductivity, Seebeck coefficient, power factor, lattice thermal conductivity and zT value in the measured temperature range (300-600 K) are shown in Figures 4 to 8 .

[0050] From Figures 2 to 8 , it can be seen that the Mg 3.07 SbBiHo 0.01 material prepared in Example 1 has a carrier concentration of 3.2 × 10 19 cm -3 at room temperature, and a carrier mobility of 98 cm2 V -1 s -1 , electrical conductivity σ is 5 × 10 4 S m -1 . The maximum power factor PF is 14.4 μW cm -1 K -2 , and the lowest lattice thermal conductivity is 0.62 W m -1 K -1 . The thermoelectric figure of merit zT is 0.86 at 600 K. The Mg 3.05 SbBiHo 0.03 material prepared in Example 2 has a carrier concentration of 4.5 × 10 19 cm -3 at room temperature, a carrier mobility of 104 cm 2 V -1 s -1 , and an electrical conductivity σ of 7.5 × 10 4 S m -1 . The maximum power factor PF is 16.7 μW cm -1 K -2 , and the lowest lattice thermal conductivity is 0.59 W m -1 K -1 . The thermoelectric figure of merit zT is 0.96 at 600 K. The Mg 3.03 SbBiHo 0.05 material prepared in Example 3 has a carrier concentration of 5.5 × 10 19 cm -3 at room temperature, which is 2 orders of magnitude higher than that of the base (i.e., the Mg 3.08 SbBi material prepared in Comparative Example 1). The combined melt preparation and large-particle SPS process ensures a large grain size and a high carrier mobility, with a room-temperature carrier mobility of 122 cm 2 V -1 s -1 and an electrical conductivity σ of 10.7 × 10 4 S m -1 . The maximum power factor PF is 19.7 μW cm -1 K -2 , and the lowest lattice thermal conductivity is 0.54 W m -1 K -1 . The thermoelectric figure of merit zT is 1.07 at 600 K, which is 75% higher than that of the base (the Mg 3.08 SbBi material prepared in Comparative Example 1). The Mg 3.01 SbBiHo 0.07 material prepared in Example 4 has a carrier concentration of 5.8 × 10 19 cm-3 The melt preparation combined with the large particle SPS process ensures a large grain size and a high carrier mobility, with a room temperature carrier mobility of 128 cm 2 V -1 s -1 The electrical conductivity σ is 12.3 × 10 4 S m -1 The maximum power factor PF is 19.7 μW cm -1 K -2 , which is nearly 10 times higher than that of the matrix (Mg 3.08 SbBi material prepared in Comparative Example 1). The lowest lattice thermal conductivity is 0.5 W m - 1 K -1 , which is 50% lower than that of the matrix material (Mg 3.08 SbBi material prepared in Comparative Example 1). The thermoelectric figure of merit zT thereof is 1.08 at 600 K, which is 75% higher than that of the Mg3SbBi matrix, and the Mg3SbBiHo 0.08 material prepared in Example 5 has a carrier concentration of 7.1 × 10 19 cm -3 at room temperature. The room temperature carrier mobility is 108 cm 2 V -1 s -1 The electrical conductivity σ is 11.8 × 10 4 S m -1 The maximum power factor PF is 19.8 μW cm -1 K -2 , and the lowest lattice thermal conductivity is 0.49 W m -1 K -1 The thermoelectric figure of merit zT thereof is 1.07 at 600 K.

[0051] In summary, the Ho-doped Mg3SbBi-based thermoelectric material of the present application has the following advantages compared with the prior art: 1) by doping the lanthanide element Ho in Mg3SbBi, a higher carrier concentration is obtained, which improves the electrical transport performance of the material. 2) The lattice low thermal conductivity of the prepared Mg3SbBi material is lower, which significantly improves the thermoelectric performance of Mg3SbBi. 3) By using a melting method to dope the lanthanide element Ho in Mg3SbBi, the production equipment requirement is low, and the controllability and repeatability of sample preparation are good.

[0052] The preparation method of the Ho-doped Mg3SbBi-based thermoelectric material of the present application greatly improves the carrier concentration and the electric transport performance of the sample by doping lanthanide element Ho at the Mg site due to the lower electronegativity difference and the higher doping amount. Meanwhile, the point defect scattering introduced by the large mass difference between Ho and Mg elements significantly reduces the lattice thermal conductivity, and thus a high thermoelectric figure of merit zT is obtained in the Ho-doped Mg3SbBi sample. The preparation method is simple, the operation condition is mild and easy to control, and is suitable for large-scale industrial production, and has popularization and application value in the field of new energy material technology.

[0053] The above examples are only preferred embodiments for fully illustrating the present application, and the protection scope of the present application is not limited thereto. Any equivalent replacement or transformation made by the person skilled in the art on the basis of the present application is within the protection scope of the present application.

Claims

1. A Ho-doped Mg3SbBi-based thermoelectric material, characterized in that, The Ho-doped Mg3SbBi-based thermoelectric material has a chemical formula of Mg 3.08-x SbBiHo x wherein x is in a range of 0 ≤ x ≤ 0.

08.

2. The Ho-doped Mg3SbBi-based thermoelectric material of claim 1, wherein, The Ho-doped Mg3SbBi-based thermoelectric material is an n-type thermoelectric material.

3. The method of producing Ho-doped Mg3SbBi-based thermoelectric material according to claim 1 or claim 2, characterized by, The method comprises the following steps: S1, sealing solid-state elements of magnesium (Mg), antimony (Sb), bismuth (Bi) and holmium (Ho) in a tantalum tube or a stainless steel crucible, and melting into an ingot in a vacuum; S2, grinding the ingot to obtain alloy particles; S3, the particles are subjected to discharge plasma sintering to obtain Ho-doped Mg3SbBi-based thermoelectric material, i.e., Mg 3.08- x SbBiHo x thermoelectric material.

4. The method of claim 3, wherein the Ho-doped Mg3SbBi-based thermoelectric material is prepared by a process comprising: In the S1, the temperature is raised from room temperature to 1273-1423 K in 10-12 h, the melting is kept at a temperature of 1273-1423 K for 20-24 h, and the cooling mode of melting is furnace cooling to room temperature.

5. The method of claim 3, wherein the Ho-doped Mg3SbBi-based thermoelectric material is prepared by a process comprising: In the S1, the ingot is prepared by sealed melting with tantalum tube and quartz tube, the tantalum tube is sealed in argon atmosphere, the vacuum degree is 10 1 ~10 2 Pa, the vacuum degree of the sealed quartz tube is 10 -1 ~10 0 Pa.

6. The method of claim 3, wherein the Ho-doped Mg3SbBi-based thermoelectric material is prepared by a process comprising: In the S3, the temperature of the spark plasma sintering is 893-923 K, the pressure is 45-55 Mpa, and the sintering time is 2-3 min.

7. The method of claim 3, wherein the Ho-doped Mg3SbBi-based thermoelectric material is prepared by a process comprising: preparing a Mg3SbBi-based thermoelectric material; and doping the Mg3SbBi-based thermoelectric material with Ho. In the S2, the ingot is ground manually with an agate mortar in a glove box.

8. The method of claim 3, wherein the Ho-doped Mg3SbBi-based thermoelectric material is prepared by a process comprising: preparing a Mg3SbBi-based thermoelectric material; and doping the Mg3SbBi-based thermoelectric material with Ho. In the S2, the ingot is sieved after grinding, so that the particle size of the alloy particles is 1-2 mm.

9. The method of claim 3, wherein the Ho-doped Mg3SbBi-based thermoelectric material is prepared by a process comprising: preparing a Mg3SbBi-based thermoelectric material; and doping the Mg3SbBi-based thermoelectric material with Ho. The magnesium (Mg) is selected from magnesium (Mg) particles, and the purity of the magnesium (Mg) particles is 99.5 wt%-99.95 wt%; And / or, the antimony (Sb) is selected from antimony (Sb) pellets, and the purity of the antimony (Sb) pellets is 99.99 wt%-99.999 wt%; And / or, the bismuth (Bi) is selected from bismuth (Bi) particles, and the purity of the bismuth (Bi) particles is 99.99 wt%-99.999 wt%; And / or, the holmium (Ho) is selected from holmium (Ho) blocks, and the purity of the holmium (Ho) blocks is 99.9 wt%-99.999 wt%.

10. Use of the Ho-doped Mg3SbBi-based thermoelectric material of claim 1 or claim 2 as a heat-to-electricity conversion material.

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