TiCoSb-based semi-hassle single crystal thermoelectric material, preparation method thereof and thermoelectric device

Abstract

The application provides a TiCoSb-based half-Hasle single crystal thermoelectric material, and the chemical formula of the TiCoSb-based half-Hasle single crystal thermoelectric material is Ti 1‑x‑y M x R y CoSb; wherein the M element comprises at least one of an Nb element, a Ta element, an Sc element and a V element, the R element comprises at least one of a Zr element and an Hf element, x is not greater than 0.07, and y is not greater than 0.25. The application provides a TiCoSb-based half-Hasle single crystal thermoelectric material, a preparation method and a thermoelectric device, the performance of the TiCoSb-based half-Hasle single crystal thermoelectric material is controlled by doping M elements and alloying R metal elements in Ti positions according to a proportion; the suitable carrier concentration required by the thermoelectric material is provided by the heterovalent doping effect of different proportions of M elements, so that the power factor PF of the material is improved, and the electrical performance of the material is improved; the scattering point of phonons is provided by the isoelectronic alloying effect of different proportions of R elements, the thermal conductivity of the material is reduced, and the prepared Ti 1‑x‑y M x R y CoSb single crystal has good thermoelectric performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermoelectric materials, and particularly relates to a TiCoSb-based semi-Hoelzer single crystal thermoelectric material, a preparation method and a thermoelectric device. BACKGROUND

[0002] Thermoelectric generation is a technology that converts heat energy directly into electricity using the Seebeck effect. At present, the Seebeck effect of semiconductor materials is outstanding in the field of thermoelectric generation. The device prepared has the characteristics of small size, no moving parts, compact structure, maintenance-free, no noise, high reliability, etc. In deep space exploration and field emergency power supply, the semiconductor Seebeck effect has been important application. In addition, it has broad application prospects and economic benefits in the field of thermoelectric generation of industrial waste heat and automobile exhaust waste heat recovery.

[0003] One of the important indicators for measuring the thermoelectric conversion efficiency of thermoelectric generation is the structural performance of semiconductor materials. The thermoelectric performance of the material is usually described by a dimensionless thermoelectric figure of merit zT, where zT=S 2 σT / κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity. The higher the zT value, the higher the thermoelectric conversion efficiency of the thermoelectric generation device. Therefore, an ideal thermoelectric material needs to have both high power factor (S 2 σ) and low thermal conductivity. However, it is difficult to simultaneously optimize these three parameters due to the interdependence between the thermoelectric parameters (S, σ, and κ), and therefore it is challenging to obtain a high zT value. Among them, optimizing the material mobility can effectively improve the power factor PF of the material without deteriorating the Seebeck coefficient and thermal conductivity, thereby improving the zT value of the material.

[0004] Semi-Hoelzer materials are a new type of thermoelectric material suitable for medium and high temperature intervals, with good high temperature stability, mechanical properties and excellent power factor PF, and the raw materials are relatively inexpensive, so they have important application and research value. Usually, high-purity elemental metals are often used to synthesize bulk raw materials by melting to prepare semi-Hoelzer materials, including non-equilibrium synthesis paths such as suspension melting, ball milling and spark plasma sintering to obtain polycrystalline semi-Hoelzer thermoelectric materials. However, these types of polycrystalline semi-Hoelzer materials often have a large number of defects, which cause the material performance to be non-uniform and unstable; in addition, there are often a large number of second phase impurities in polycrystalline materials, which reduce the purity of the material. Including but not limited to the above problems, the theoretical and actual Hall mobility of semi-Hoelzer thermoelectric materials differs greatly, which affects the improvement of the thermoelectric performance of semi-Hoelzer materials. Although polycrystalline semi-Hoelzer materials meet the demand of thermoelectric conversion to some extent, the problems of performance stability, uniformity and purity still limit their further development and popularization in practical applications.

[0005] At present, the single crystal of the half-Heusler material is mainly grown by a melting growth method and a chemical vapor transport method. The melting growth method requires preparing a high-purity alloy, heating and melting the alloy, and then injecting the alloy into a crucible to grow a crystal under appropriate conditions. The chemical vapor transport method needs to mix powders of the required elements, place the powders in a quartz tube to establish a temperature gradient, and introduce a suitable carrier gas into the tube. The elements react to form a half-Heusler material at a high-temperature region, and finally a single crystal is deposited at a low-temperature region. Regardless of which method is used, the growth conditions, including temperature, pressure, composition, and crystal growth rate, need to be strictly controlled. However, the existing preparation methods usually have high energy consumption and complex processes, so it is difficult to obtain large-size half-Heusler material single crystals at low cost and energy consumption.

[0006] TiCoSb material has attracted widespread attention due to its large Seebeck coefficient and good thermal stability. However, due to the low mobility of the polycrystalline TiCoSb material, the theoretical and actual power factors PF are greatly different, which limits the performance improvement of the TiCoSb-based half-Heusler thermoelectric material. The current mainstream growth method of the half-Heusler single crystal has inherent disadvantages, making it difficult and complex to optimize the performance of the single crystal. Therefore, the cost and effect of the performance optimization of the single crystal TiCoSb-based half-Heusler thermoelectric material are not ideal. In summary, it is urgent for researchers to improve it. SUMMARY

[0007] The purpose of the present application is to at least overcome one of the deficiencies of the prior art, and to provide a TiCoSb-based half-Heusler single crystal thermoelectric material, a preparation method and a thermoelectric device, which can obtain a high-performance Ti 1-x-y M x R y CoSb single crystal thermoelectric material, and effectively remove impurities and defects in the crystal during the growth process, thereby ensuring that the prepared Ti 1-x-y M x R y CoSb single crystal has good thermoelectric performance.

[0008] The technical solution of the present application is: a TiCoSb-based half-Heusler single crystal thermoelectric material, the chemical formula of the TiCoSb-based half-Heusler single crystal thermoelectric material is Ti 1-x-y M x R y CoSb; wherein, M element includes at least one of Nb element, Ta element, Sc element, V element, R element includes at least one of Zr element, Hf element, and x is not greater than 0.07, y is not greater than 0.25.

[0009] As a further improvement of the technical solution, the chemical formula of the TiCoSb-based half-Heusler single crystal thermoelectric material is Ti1-x-y Nb x Hf y CoSb.

[0010] As a further improvement of the technical solution, x = 0.04-0.06, y = 0.03-0.06.

[0011] The application also provides a preparation method of a TiCoSb-based semi-Hasle single crystal thermoelectric material.

[0012] The preparation raw material step is to prepare a raw material according to the stoichiometric ratio of Ti 1-x-y M x R y CoSb, wherein the M element includes any one of Nb element, Ta element, Sc element and V element, the R element includes any one of Zr element and Hf element, and x is not greater than 0.07 and y is not greater than 0.25;

[0013] The packaging step is to seal the raw material in a packaging tube under high vacuum;

[0014] The heating step is to place the packaging tube into a heating furnace for heating, so that the raw material is melted to form a mixed melt;

[0015] The crystallization step is to cool the heating furnace at a set rate to obtain a Ti 1-x-y M x R y CoSb single crystal thermoelectric material.

[0016] As a further improvement of the technical solution, the preparation raw material step further includes adding Sb single metal as a fluxing agent in the raw material; and the molar ratio of the fluxing agent to the Ti element is 10-35 times.

[0017] As a further improvement of the technical solution, in the heating step, the heating furnace is heated to a set temperature and kept at the set temperature for a set time, wherein the set temperature is 1100-1150°C; and the set time is 24-72h.

[0018] As a further improvement of the technical solution, the preparation method further includes a centrifugation step after the crystallization step, the fluxing agent is spun out by a centrifuge to obtain a Ti 1-x-y M x R y CoSb single crystal thermoelectric material.

[0019] As a further improvement of the technical solution, in the packaging step, air is extracted to achieve a high-vacuum sealed environment; and the vacuum degree of the high vacuum is less than 1x10-3 ~1x10 -4 Pa.

[0020] As a further improvement of the technical solution, in the heating step, the heating furnace is a pit furnace, and the temperature rising speed of the pit furnace is 10-15℃ / min; in the crystallization step, the temperature falling speed of the pit furnace is 0.1-4℃ / h; in the centrifugation step, the centrifugation temperature of the fluxing agent is 760-900℃.

[0021] The application further provides a thermoelectric device, which has the TiCoSb-based semi-Hasler single crystal thermoelectric material.

[0022] The TiCoSb-based semi-Hasler single crystal thermoelectric material has a chemical formula of Ti 1-x-y M x R y CoSb; wherein the M element includes at least one of Nb element, Ta element, Sc element and V element, the R element includes at least one of Zr element and Hf element, x is not greater than 0.07, and y is not greater than 0.25. The TiCoSb-based semi-Hasler single crystal thermoelectric material, the preparation method and the thermoelectric device provided by the application realize performance control of the TiCoSb-based semi-Hasler single crystal thermoelectric material by doping M elements and alloying R metal elements at Ti sites in a certain proportion; the required suitable carrier concentration of the thermoelectric material is provided by the heterovalent doping effect of different proportions of M elements, so as to improve the power factor PF of the material and thus improve the electrical performance of the material; the scattering point of phonons is provided by the isoelectronic alloying effect of different proportions of R elements, so as to reduce the thermal conductivity of the material and improve the thermal performance of the material, and thus a high-performance Ti 1-x- y M x R y CoSb single crystal thermoelectric material is obtained. 1-x-y M x R y CoSb single crystal has good thermoelectric performance. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0024] Figure 1(a) is a photograph of a TiCoSb single crystal in Example 1 of the present application;

[0025] Figure 1(b) is an X-ray diffraction pattern of a TiCoSb single crystal in Example 1 of the present application;

[0026] Figure 1(c) is an oriented X-ray diffraction pattern of a TiCoSb single crystal in Example 1 of the present application;

[0027] Figure 1(d) is the X-ray diffraction-oscillation curve test result of a TiCoSb single crystal in Example 1 of the present application;

[0028] Figure 2(a) is a graph of the resistivity of a Ti 1-x Nb x CoSb single crystal versus temperature in Example 2 of the present application;

[0029] Figure 2(b) is a graph of the Seebeck coefficient of a Ti 1-x Nb x CoSb single crystal versus temperature in Example 2 of the present application;

[0030] Figure 2(c) is a graph of the mobility of a Ti 1-x Nb x CoSb single crystal versus other polycrystalline materials in Example 2 of the present application;

[0031] Figure 2(d) is a graph of the power factor of a Ti 1-x Nb x CoSb single crystal at different temperatures in Example 2 of the present application;

[0032] Figure 2(e) is a graph of the power factor versus mobility of a Ti 1-x Nb x CoSb single crystal in Example 2 of the present application;

[0033] Figure 2(f) is a graph of the average power factor of a Ti 1-x Nb x CoSb single crystal versus other TiCoSb-based polycrystalline materials in Example 2 of the present application;

[0034] Figure 3(a) is a backscattered electron image of a TiCoSb single crystal in Example 1 of the present application;

[0035] Figure 3(b) is a backscattered electron image of a Ti 1-x Nb x CoSb single crystal in Example 2 of the present application;

[0036] Figure 3(c) is a backscattered electron image of a Ti 1-x Ta x CoSb single crystal in Example 6 of the present application;

[0037] Figure 3(d) is a plot of the total thermal conductivity of Ti 1-y Hf y Figure 3(d) is a plot of the total thermal conductivity of Ti

[0038] Figure 3(e) is a plot of the total thermal conductivity of Ti 0.89 Nb 0.05 Hf 0.06 Figure 3(e) is a plot of the total thermal conductivity of Ti

[0039] Figure 4(a) is a plot of the total thermal conductivity of Ti 1-x Nb x Figure 4(a) is a plot of the total thermal conductivity of Ti

[0040] Figure 4(b) is a plot of the electronic thermal conductivity of Ti 1-x Nb x Figure 4(b) is a plot of the electronic thermal conductivity of Ti

[0041] Figure 4(c) is a plot of the lattice thermal conductivity of Ti 1-x Nb x Figure 4(c) is a plot of the lattice thermal conductivity of Ti

[0042] Figure 4(d) is a plot of the thermoelectric figure of merit of Ti 1-x Nb x Figure 4(d) is a plot of the thermoelectric figure of merit of Ti

[0043] Figure 5(a) is a plot of the total thermal conductivity of Ti 1-y Hf y Figure 5(a) is a plot of the total thermal conductivity of Ti

[0044] Figure 5(b) is a plot of the lattice thermal conductivity of Ti 1-y Hf y Figure 5(b) is a plot of the lattice thermal conductivity of Ti

[0045] Figure 6(a) is a plot of the resistivity of Ti 1-x-y Nb x Hf y Figure 6(a) is a plot of the resistivity of Ti

[0046] Figure 6(b) is a plot of the Seebeck coefficient of Ti 1-x-y Nb x Hf y Figure 6(b) is a plot of the Seebeck coefficient of Ti

[0047] Figure 6(c) is a plot of the total thermal conductivity of Ti 1-x-y Nb x Hf y Figure 6(c) is a plot of the total thermal conductivity of Ti

[0048] Figure 6(d) is a thermoelectric figure of merit of the Ti 1-x-y Nb x Hf y CoSb single crystal;

[0049] Figure 7(a) is a resistivity of the Ti 1-x Ta x CoSb single crystal as a function of temperature;

[0050] Figure 7(b) is a Seebeck coefficient of the Ti 1-x Ta x CoSb single crystal as a function of temperature;

[0051] Figure 7(c) is a total thermal conductivity of the Ti 1-x Ta x CoSb single crystal;

[0052] Figure 7(d) is a thermoelectric figure of merit of the Ti 1-x Ta x CoSb single crystal;

[0053] Figure 8(a) is a resistivity of the Ti 0.98 Sc 0.02 CoSb single crystal at low temperature;

[0054] Figure 8(b) is a Seebeck coefficient of the Ti 0.98 Sc 0.02 CoSb single crystal at low temperature;

[0055] Figure 8(c) is a power factor of the Ti 0.98 Sc 0.02 CoSb single crystal at low temperature;

[0056] Figure 8(d) is a thermal conductivity of the Ti 0.98 Sc 0.02 CoSb single crystal at low temperature;

[0057] Figure 9(a) is a resistivity of the Ti 0.97 V 0.03 CoSb single crystal at low temperature;

[0058] Figure 9(b) is a Seebeck coefficient of the Ti 0.97 V 0.03 CoSb single crystal at low temperature;

[0059] Figure 9(c) is a power factor of the Ti 0.97 V 0.03Power factor map of CoSb single crystal at low temperature;

[0060] Figure 9(d) is a Ti 0.97 V 0.03 Thermal conductivity map of CoSb single crystal at low temperature;

[0061] Figure 10 is a Ti 1-y Zr y Thermal conductivity map of CoSb single crystal at different temperatures;

[0062] Figure 11(a) is a Ti 0.84 Nb 0.06 Hf 0.10 Resistivity map of CoSb single crystal;

[0063] Figure 11(b) is a Ti 0.84 Nb 0.06 Hf 0.10 Seebeck coefficient map of CoSb single crystal;

[0064] Figure 11(c) is a Ti 0.84 Nb 0.06 Hf 0.10 Power factor map of CoSb single crystal;

[0065] Figure 11(d) is a Ti 0.84 Nb 0.06 Hf 0.10 Thermal conductivity map of CoSb single crystal. DETAILED DESCRIPTION

[0066] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0067] It should be noted that the terms "set", "connected" should be understood broadly, for example, it can be directly set, connected, or indirectly set, connected through a centering component, a centering structure.

[0068] In addition, in the embodiments of the present application, the terms indicating the orientation or position relationship such as "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like are based on the orientation or position relationship shown in the drawings or the conventional placement state or use state, which are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the structures, features, devices or elements referred to must have a particular orientation or position relationship, nor must be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specified.

[0069] In the specific technical features and embodiments described in the specific embodiments, any suitable combination can be combined without contradiction, for example, different specific technical features / embodiments can form different embodiments by combination. In order to avoid unnecessary repetition, various possible combinations of various specific technical features / embodiments in the present application are not described again.

[0070] The embodiment of the present application provides a high-performance TiCoSb-based half-Hasle single crystal thermoelectric material, and the chemical formula of the TiCoSb-based half-Hasle single crystal thermoelectric material is Ti 1-x-y M x R y CoSb; wherein the M element includes at least one of a Nb element, a Ta element, a Sc element and a V element, the R element includes at least one of a Zr element and a Hf element, x is not greater than 0.07, and y is not greater than 0.25. Specifically, the M element can be any one or a mixed element of two or more of the Nb element, the Ta element, the Sc element and the V element, and the R element is any one or a mixed element of two or more of the Zr element and the Hf element; through the heterovalent doping effect of different proportions of M elements, a suitable carrier concentration required by the thermoelectric material is provided, so as to improve the power factor PF of the material and improve the electrical performance of the material; through the isoelectronic alloying effect of introducing different proportions of R elements, scattering points of phonons are provided, so as to reduce the thermal conductivity of the material and improve the thermal performance of the material, and therefore a high-performance Ti 1-x-y M x R y CoSb single crystal thermoelectric material is obtained.

[0071] Further, the chemical formula of the TiCoSb-based half-Hasle single crystal thermoelectric material is Ti 1-x-y Nb x Hf yCoSb. Namely, the M element is Nb element, the R element is Hf element, the M element provides the suitable carrier concentration required by the thermoelectric material, the R element introduces the isoelectronic alloying of different proportions of elements, provides the scattering point of phonon, and can effectively reduce the thermal conductivity of the material. In the embodiment, x=0.04-0.06, y=0.03-0.06, and specific details are described in embodiments 3-10.

[0072] The embodiment of the present application also provides a thermoelectric device, which has the TiCoSb-based semi-Hasle single crystal thermoelectric material.

[0073] The embodiment of the present application also provides a preparation method of the TiCoSb-based semi-Hasle single crystal thermoelectric material, which is used for preparing the TiCoSb-based semi-Hasle single crystal thermoelectric material, and includes the following steps: a raw material preparation step, a packaging step, a heating step and a crystallization step.

[0074] The raw material preparation step is to prepare the raw material according to the stoichiometric ratio of Ti 1-x-y M x R y CoSb, wherein the M element includes any one of Nb element, Ta element, Sc element and V element, the R element includes any one of Zr element and Hf element, x is not more than 0.07, and y is not more than 0.25; specifically, the elemental metal Sb, Ti, Co, M and R with a purity of 99.99% are weighed as raw materials according to the molar ratio; the molar ratio of Ti, Co, M and R is 1:1:x:y, x is not more than 0.07, and y is not more than 0.25.

[0075] The packaging step is to seal the raw material in a packaging tube under high vacuum; specifically, after the raw material is loaded in the packaging tube, the raw material is sealed in the internal part of the packaging tube under high vacuum. Then, a quartz glass plug is sealed on the internal part of the packaging tube to maintain the vacuum state of the internal part of the packaging tube to prevent the raw material from being oxidized, so as to control the melt composition. The high vacuum can be obtained by a mechanical pump or a molecular pump; in the embodiment, the mechanical pump is used to extract air to achieve a high-vacuum sealing environment; the vacuum degree of the high vacuum is lower than 1x10 -3 ~1x10 -4 Pa. The packaging tube can be a common quartz glass tube, a high-purity quartz glass tube or a common quartz glass tube nested with an Al2O3 corundum tube.

[0076] The heating step is to place the packaging tube into a heating furnace to heat and melt the raw material to form a mixed melt.

[0077] The crystallization step is to cool the heating furnace at a set rate to obtain the Ti 1-x-y M x Ry CoSb single crystal thermoelectric material.

[0078] Further, the preparation raw material step also includes adding Sb single metal as fluxing agent in the raw material; the molar ratio of the fluxing agent is 10-35 times of the Ti element. In this embodiment, the raw material and fluxing agent (specifically the molar ratio of Ti, Co, and fluxing agent) are loaded into a common quartz glass tube according to a molar ratio of 1:1:25, a high vacuum environment is obtained by using a mechanical pump for sealing of the quartz glass plug, and the melt composition is controlled. The Sb single metal is used as the fluxing agent, which can avoid rapid crystallization caused by supersaturation by controlling the proportion of the fluxing agent, thereby reducing the formation of defects; secondly, the metal fluxing agent Sb has good solubility to Ti and Co and other target raw materials, and poor solubility to other substances that can form impurities. This selective dissolution helps to reduce the crystallization of non-target substances, thereby inhibiting the introduction of impurities. Therefore, the Sb raw material is selected as the fluxing agent, which can inhibit impurities and defects in the grown single crystal. The furnace is started to heat and keep warm, so that the raw material is fully melted and uniform to become a molten state, and the fluxing agent reacts with the material to be grown or forms a melt in this state.

[0079] Further, in the heating step, the heating furnace is heated to a set temperature and kept warm for a set time, wherein the set temperature is 1100-1150°C; and the set time is 24-72h, so that the mixed melt forms a uniform melt. In this embodiment, the furnace is heated to 1100°C at a heating rate of 10°C / min and kept warm for 48h, so that the raw material is fully and uniformly melted.

[0080] Further, the preparation method further includes a centrifugation step after the crystallization step, the excess Sb fluxing agent is spun out by a centrifuge, and Ti 1-x-y M x R y CoSb single crystal thermoelectric material. In the centrifugation step, the centrifugation temperature of the fluxing agent is 760-900°C, the excess Sb fluxing agent is centrifuged out, and Ti 1-x-y M x R y CoSb single crystal semi-Heusler thermoelectric material.

[0081] Further, in the heating step, the heating furnace is an electric furnace, and the heating rate of the electric furnace is 10-15°C / min; in the crystallization step, the cooling rate of the electric furnace is 0.1-4°C / h.

[0082] Specifically, after the raw material is configured, the furnace is heated to 1100°C at a heating rate of 10°C / min and kept warm for 48h; after the warm-keeping phase is completed, the furnace begins to reduce the temperature of the furnace cavity, and Ti1-x-y M x R y CoSb single crystal begins to nucleate and grow. Finally, the flux is centrifuged to obtain the Ti 1-x-y M x R y CoSb single crystal thermoelectric material. Wherein, the cooling rate of the well-type furnace is 0.1-4 ℃ / h. In this embodiment, the well-type furnace starts to cool at 2 ℃ / h, and the flux Sb plays a role in inhibiting impurities and defects during the cooling process. The temperature is reduced to 760-900 ℃, and the excess Sb flux is centrifuged out after 2 min of centrifugal treatment. Finally, the Ti 1-x- y M x R y CoSb single crystal half-Heusler thermoelectric material. The Ti 1-x-y M x R y CoSb single crystal half-Heusler thermoelectric material has less defects and impurities, and the Hall mobility is much higher than that of the mainstream polycrystalline TiCoSb-based polycrystalline half-Heusler thermoelectric material, so it can significantly improve the thermoelectric performance.

[0083] The application also provides a thermoelectric device having the TiCoSb-based half-Heusler single crystal thermoelectric material in the above embodiments, thus having very superior thermoelectric performance, and having great application value and popularization prospect.

[0084] The application also provides embodiments 1, 2, and Ti 1-x-y M x R y CoSb half-Heusler single crystal thermoelectric material and its preparation method (embodiments 3-10), which are described in detail.

[0085] Embodiment 1

[0086] This example provides a Ti 1-x-y M x R y CoSb half-Heusler single crystal thermoelectric material and its preparation method, wherein x=0 and y=0, so that the chemical composition of the TiCoSb-based half-Heusler single crystal thermoelectric material is TiCoSb, and the specific steps of the preparation method are as follows:

[0087] With 99.99% metal as raw material, according to the metal flux Sb is 15 times, the molar ratio of Ti, Co is 1:1, weighing Sb, Ti, Co, the total weight of raw materials is 60 grams; the weighed raw materials are loaded into a common quartz glass tube, and a mechanical pump is used to extract high vacuum state, then a glass plug is sealed at the top 1 / 4 of the glass tube to ensure the high vacuum state inside the quartz glass tube to prevent the melt from oxidizing at high temperature, so as to effectively control the melt composition;

[0088] The sealed quartz glass tube is placed in the well-type furnace near the furnace wall, which is convenient for obtaining temperature gradient during the cooling process; the furnace door is closed and the well-type furnace heating program is started at a heating rate of 10 ℃ / min to heat to 1100 ℃ and keep for 48 h, forming a molten homogeneous melt;

[0089] After the holding time is over, the well-type furnace starts to cool down to 800 ℃ at a rate of 2 ℃ / h, and TiCoSb single crystal nucleates and grows during the process. When the furnace chamber is at 800 ℃, the quartz glass tube is taken out of the well-type furnace and centrifuged to obtain TiCoSb single crystal thermoelectric material;

[0090] The actual photo of the TiCoSb single crystal block described above is shown in Fig. 1(a), and the size of the single crystal block prepared according to the flux ratio can reach 10*10*10mm 3 left and right, and the appearance presents a typical pyramid type of half-Hasler material; the X-ray diffraction pattern of the TiCoSb single crystal block is shown in Fig. 1(b), and Fig. 1(c) shows the directional X-ray diffraction pattern of the TiCoSb single crystal, the space group of the crystal is F-43m, which is consistent with the theoretical space group, and the order degree of the crystal is high; Fig. 1(d) is the test result graph of X-ray diffraction-oscillation curve, which further proves that the TiCoSb single crystal prepared has high quality, and the half peak width (FWHM) of (111) crystal face characteristic peak is only 0.0150°. As shown in Fig. 3(a), back scattered electron energy spectrum analysis of the block material is carried out, and the results show that the generated single crystal block material is uniform in composition, and there is no segregation of Ti, Co and Sb. These results show that the dense and uniform TiCoSb single crystal thermoelectric material can be obtained by the method.

[0091] Example 2

[0092] The present example provides a TiCoSb-based half-Hasler single crystal thermoelectric material and a preparation method thereof. The TiCoSb-based half-Hasler single crystal thermoelectric material has a chemical composition of Ti 1-x-y M x R y CoSb, wherein M is Nb, x=0-0.05, and y=0, and the specific steps are as follows:

[0093] On the basis of preparing high-quality TiCoSb single crystals, Nb element is doped in Ti site to improve the carrier concentration of the material, and then improve the electrical properties of the material. With 99.99% metal elements as raw materials, the molar ratio of Ti, Co and Nb is 1:1:x, and the total weight of the raw materials is 60 grams. The subsequent operation and example 1 are the same, and Ti 1-x Nb x CoSb single crystal thermoelectric material. The prepared Ti 1- x Nb x CoSb single crystal backscattering electron spectroscopy results are shown in Figure 3(b), and the results show that the composition of the generated single crystal bulk material is uniform, and there is no segregation of Ti, Co, Sb and Nb.

[0094] A series of Ti 1-x Nb x CoSb(x=0-0.043) single crystal samples were tested for electrical properties, as shown in Figures 2(a) and 2(b), as the Nb doping content x increases, the resistivity gradually decreases, and the absolute value of the Seebeck coefficient also gradually decreases, which conforms to the electrical property change trend of doping. As shown in Figure 2(c), the high-quality Ti 1- x Nb x CoSb single crystal has a mobility of 2-3 times that of the same type of polycrystalline material under the same carrier concentration. As can be clearly seen from Figure 2(e), it is precisely due to the significant improvement in mobility that the power factor PF of the material has greatly. As shown in Figure 2(d), the power factor PF of the single crystal prepared in this embodiment is higher than that of the same type of TiCoSb-based polycrystalline material with excellent performance at all temperatures, so the average power factor PF in Figure 2(f) ave is much higher than that of the same system polycrystalline material, which can reach ~40μWcm -1 K -2 .

[0095] A series of Ti 1-x Nb x CoSb(x=0-0.043) single crystal samples were tested for thermal properties, as shown in Figures 4(a), 4(b) and 4(c), as the Nb doping content increases, the electronic thermal conductivity κ e gradually increases, while the lattice thermal conductivity κ l changes little, but since the electronic thermal conductivity accounts for a small proportion of the total thermal conductivity κ total , the total thermal conductivity κ total changes little. Finally, due to the little change in thermal properties and the significant optimization of electrical properties, Ti0.995 Nb 0.005 The thermoelectric figure of merit zT of CoSb can reach ~0.46.

[0096] Example 3

[0097] The present example provides a TiCoSb-based half-Heusler single crystal thermoelectric material and a preparation method thereof. The TiCoSb-based half-Heusler single crystal thermoelectric material has a chemical composition of Ti 1-x-y M x R y CoSb, R is Hf, wherein x = 0, y = 0-0.22, and the specific steps are as follows:

[0098] On the basis of preparing high-quality TiCoSb single crystals, Hf elements are alloyed at the Ti site to increase the degree of phonon scattering, reduce the lattice thermal conductivity of the material, and thus improve the thermal performance of the material. 99.99% of the metal elements are used as raw materials, the molar ratio of the metal fluxing agent Sb is 15 times, the molar ratio of Ti, Co and Hf is 1:1:y, and the total weight of the raw materials is 60 grams. The subsequent operation is the same as that of Example 1, and Ti 1-y Hf y CoSb single crystal thermoelectric material can be obtained after centrifugation. 1-y Hf y The backscattered electron energy spectrum result of the Ti 1-y Hf y CoSb single crystal is shown in FIG. 3(d), and the results show that the composition of the generated single crystal bulk material is uniform, and there is no segregation of Ti, Co, Sb and Hf.

[0099] Since no doping is performed, the carrier concentration of the material is very low, and it is meaningless to test the electrical conductivity and the Seebeck coefficient, so the Ti 1-y Hf y CoSb single crystal is not tested for electrical performance. Subsequently, a series of Ti total Hf l CoSb single crystals are tested for thermal conductivity, as shown in FIG. 5(a), and the thermal conductivity decreases significantly with the increase of the Hf doping content y, which is consistent with the thermal conductivity change trend of the isoelectronic alloying. As can be seen from FIG. 5(b), the increase of the Hf content leads to the decrease of the total thermal conductivity κ 1-y Hf y The thermal performance of the Ti 1-y Hf y CoSb single crystal is significantly optimized. However, if the content of Hf is too high, it may strongly scatter electrons, resulting in a significant decrease in the mobility of the material, which is not conducive to the performance improvement of the material.

[0100] Example 4

[0101] The present example provides a high-performance TiCoSb-based half-Heusler single crystal thermoelectric material and a preparation method thereof. The TiCoSb-based half-Heusler single crystal thermoelectric material has a chemical composition of Ti 1-x-y M x R y CoSb, wherein M is Nb, R is Hf, x = 0.05, and y = 0.03. 1-x-y M x R y CoSb is Ti 0.92 Nb 0.05 Hf 0.03 CoSb, and the specific steps are as follows:

[0102] Based on the preparation of high-quality TiCoSb single crystals, Nb and Hf elements are doped and alloyed at the Ti site to synergistically improve the electrical and thermal properties of the material. With 99.99% metal elements as raw materials, the molar ratio of metal fluxing agent Sb is 15 times, and the molar ratio of Ti, Co, and Hf is 1:1:0.05:0.03. The total weight of the raw materials is 60 grams. The subsequent operation and Example 1 are the same, and after centrifugation, Ti 0.92 Nb 0.05 Hf 0.03 CoSb single crystal thermoelectric material can be obtained. The prepared Ti 0.92 Nb 0.05 Hf 0.03 CoSb single crystal has a backscattered electron energy spectrum result as shown in FIG. 3(e), which shows that the composition of the generated single crystal bulk material is uniform, and there is no segregation of Ti, Co, Sb, Nb, and Hf.

[0103] As shown in FIG. 6, through the doping and alloying of Nb and Hf elements, the electrical and thermal properties of the material are synergistically improved, the carrier concentration is effectively improved, the degree of phonon scattering is increased within a certain range, and the Ti 0.92 Nb 0.05 Hf 0.03 CoSb can achieve a thermoelectric figure of merit zT of about 0.4.

[0104] Example 5

[0105] The present example provides a high-performance TiCoSb-based half-Heusler single crystal thermoelectric material and a preparation method thereof. The TiCoSb-based half-Heusler single crystal thermoelectric material has a chemical composition of Ti 1-x-y M x R y CoSb, wherein M is Nb, R is Hf, x = 0.05, and y = 0.03.

[0106] On the basis of preparing high-quality TiCoSb single crystals, Nb and Hf elements are doped and alloyed at the Ti site to synergistically improve the electrical and thermal properties of the material. 99.99% metal elements are used as raw materials, the molar ratio of metal fluxing agent Sb is 15 times, and the molar ratio of Ti, Co and Hf is 1:1:0.05:0.06. The total weight of the raw materials is 60 grams. The subsequent operations are the same as in Example 1, and Ti 0.89 Nb 0.05 Hf 0.06 CoSb single crystal thermoelectric material. The prepared Ti 0.89 Nb 0.05 Hf 0.06 CoSb single crystal. The backscattered electron energy spectrum results of the Ti

[0107] As shown in FIG. 6, through the doping and alloying of Nb and Hf elements, the electrical and thermal properties of the material are synergistically improved, the carrier concentration is effectively improved, the degree of phonon scattering is increased within a certain range, and the Ti 0.89 Nb 0.05 Hf 0.06 The thermoelectric figure of merit zT of the Ti

[0108] Example 6

[0109] The present example provides a high-performance TiCoSb-based half-Heusler single crystal thermoelectric material and a preparation method thereof. The TiCoSb-based half-Heusler single crystal thermoelectric material has a chemical composition of Ti 1-x-y M x R y CoSb, wherein M is Ta, x = 0-0.10, and y = 0. The specific steps are as follows:

[0110] On the basis of preparing high-quality TiCoSb single crystals, Ta is doped at the Ti site to improve the carrier concentration of the material. 99.99% metal elements are used as raw materials, the molar ratio of metal fluxing agent Sb is 15 times, and the molar ratio of Ti, Co and Ta is 1:1:x. The total weight of the raw materials is 60 grams. The subsequent operations are the same as in Example 1, and Ti 1-x Ta x CoSb single crystal thermoelectric material. In this embodiment, x = 0.05, and the prepared Ti 0.95 Ta 0.05 CoSb single crystal. The backscattered electron energy spectrum results of the Ti

[0111] As shown in FIG. 7, by doping with the element Ta, the electrical and thermal properties of the material are improved, and the carrier concentration is effectively improved. Due to the existence of mass and stress fluctuations, the TiCoSb single crystal doped with Ta has a higher carrier concentration than the TiCoSb single crystal. 1-x Ta x The thermoelectric figure of merit zT of the CoSb single crystal thermoelectric material can reach about 0.53.

[0112] Example 7

[0113] The present example provides a high-performance TiCoSb-based semi-Hasler single crystal thermoelectric material and a preparation method thereof. The TiCoSb-based semi-Hasler single crystal thermoelectric material has a chemical composition of Ti 1-x-y M x R y CoSb, wherein M is Sc, wherein x = 0.02, y = 0, and the specific steps are as follows:

[0114] On the basis of preparing a high-quality TiCoSb single crystal, Sc doping is performed at the Ti site to improve the carrier concentration of the material. With 99.99% metal elements as raw materials, the molar ratio of the metal fluxing agent Sb is 15 times, and the molar ratio of Ti, Co and Sc is 1:1:x. The total weight of the raw materials is 60 grams. The subsequent operation is the same as that of Example 1, and a Ti 0.98 Sc 0.02 CoSb single crystal thermoelectric material.

[0115] The low-temperature thermoelectric properties of the material are shown in FIG. 8. By doping with the element Sc, the material is p-type doped, the carrier concentration is effectively improved, and the electrical properties are improved. Figures 8(a)-8(d)

[0116] Example 8

[0117] The present example provides a high-performance TiCoSb-based semi-Hasler single crystal thermoelectric material and a preparation method thereof. The TiCoSb-based semi-Hasler single crystal thermoelectric material has a chemical composition of Ti 1-x-y M x R y CoSb, wherein M is Sc, wherein x = 0.02, y = 0, and the specific steps are as follows: 1-x-y M x R y CoSb, wherein M is Sc, wherein x = 0.02, y = 0, and the specific steps are as follows: 0.97 V 0.03 CoSb, wherein M is Sc, wherein x = 0.02, y = 0, and the specific steps are as follows:

[0118] ​On the basis of preparing high-quality TiCoSb single crystals, Sc doping is carried out at the Ti site to improve the carrier concentration of the material. 99.99% metal elements are used as raw materials, the molar ratio of Ti, Co and V is 1:1:x, and the total weight of the raw materials is 60 grams. The subsequent operation and example 1 are the same, and Ti 0.97 V 0.03 CoSb single crystal thermoelectric material.

[0119] The low-temperature thermoelectric performance of the material is shown in Figures 9(a)-9(d) By doping V elements, the material is also p-type doped, and the performance is improved.

[0120] Example 9

[0121] The present example provides a high-performance TiCoSb-based half-Hasle single crystal thermoelectric material and a preparation method thereof. The TiCoSb-based half-Hasle single crystal thermoelectric material has a chemical composition of Ti 1-x-y M x R y CoSb, wherein R is Zr, wherein x=0, y=0-0.20, and the specific steps are as follows:

[0122] On the basis of preparing high-quality TiCoSb single crystals, Zr is alloyed alone at the Ti site to improve the scattering point of phonons, increase the mass and stress fluctuation. 99.99% metal elements are used as raw materials, the molar ratio of Ti, Co and Zr is 1:1:y, and the total weight of the raw materials is 60 grams. The subsequent operation and example 1 are the same, and Ti 1-y Zr y CoSb single crystal thermoelectric material.

[0123] The high-temperature thermal conductivity of the material is shown in Figure 10 By alloying Zr elements, Zr atoms with large differences in atomic size, mass and vibration characteristics are introduced into the matrix, affecting the mode and rate of heat conduction, leading to increased phonon scattering and thus reduced thermal conductivity.

[0124] Example 10

[0125] The present example provides a high-performance TiCoSb-based half-Hasle single crystal thermoelectric material and a preparation method thereof. The TiCoSb-based half-Hasle single crystal thermoelectric material has a chemical composition of Ti 1-x-y M x R y CoSb, wherein M is Nb and R is Zr, wherein x=0.06 and y=0.10, and the specific steps are as follows:

[0126] On the basis of preparing high-quality TiCoSb single crystals, Nb and Zr elements are doped and alloyed at the Ti site to synergistically improve the electrical and thermal properties of the material. 99.99% pure metal elements are used as raw materials, the molar ratio of metal fluxing agent Sb is 15 times, the molar ratio of Ti, Co and Hf is 1:1:0.06:0.10, and the total weight of the raw materials is 60 grams. The subsequent operation and example 1 are the same, and Ti 0.84 Nb 0.06 Zr 0.10 CoSb single crystal thermoelectric material.

[0127] Through the doping and alloying of Nb and Zr elements, the electrical and thermal properties of the material are synergistically improved, and the carrier concentration is effectively improved. As shown in Figure 11(d), the phonon scattering range is greatly increased, so the thermal conductivity in the whole temperature range is significantly reduced, and the performance is greatly improved.

[0128] Compared with the prior art, in the above examples of the present application, by doping M elements and alloying R metal elements at the Ti site according to the proportion, the performance regulation of TiCoSb-based half-Hasle single crystal thermoelectric material is realized; through the heterovalent doping effect of different proportions of M elements, the appropriate carrier concentration required by the thermoelectric material is provided to improve the power factor PF of the material and improve the electrical performance of the material; through the isoelectronic alloying effect of different proportions of R elements, scattering points of phonons are provided to reduce the thermal conductivity of the material and improve the thermal performance of the material, so that high-performance Ti 1-x-y M x R y CoSb single crystal thermoelectric material.

[0129] Compared with the prior art, in the above examples of the present application, the metal fluxing agent method is used to realize the equilibrium state preparation of Ti 1-x-y M x R y CoSb single crystal, high-vacuum sealed tubes are used to inhibit oxidation during the melting growth process and control the melt composition; the well-type furnace is used for heating and heat preservation, so that the raw materials are fully melted into a molten state, and in the molten state, the metal Sb fluxing agent reacts with the raw materials or forms a solution; then the well-type furnace starts to cool down at a certain cooling rate, and by adjusting the cooling rate, the Ti 1-x-y M x R y CoSb single crystal gradually nucleates and grows; finally, the excess fluxing agent is centrifuged to obtain pure Ti 1-x- y M x R yCoSb single crystal thermoelectric material. Metal Sb flux in Ti 1-x-y M x R y Impurities and defects in the crystal can be effectively removed during the growth process of CoSb single crystal, thereby ensuring that the prepared Ti 1-x-y M x R y Good thermoelectric performance of CoSb single crystal.

[0130] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement or improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A TiCoSb-based half-Heusler single crystal thermoelectric material, characterized in that, The TiCoSb-based semi-Hasle single crystal thermoelectric material has a chemical formula of Ti 1-x-y M x R y CoSb; wherein the M element includes at least one of an Nb element, a Ta element, an Sc element, and a V element; the R element includes at least one of a Zr element and an Hf element, x is not greater than 0.07, y is not greater than 0.25, and the size of the single crystal is 10*10*10 mm 3 .

2. The TiCoSb-based semihalze single crystal thermoelectric material of claim 1, wherein, The TiCoSb-based half-Heusler single crystal thermoelectric material has a chemical formula of Ti 1-x-y Nb x Hf y CoSb.

3. The TiCoSb-based semihalze single crystal thermoelectric material of claim 2, wherein, x=0.04~0.06, y=0.03~0.

06.

4. A method of producing a TiCoSb-based half-Heusler single crystal thermoelectric material, characterized by, The preparation method is used for preparing the TiCoSb-based semi-Hasle single crystal thermoelectric material according to any one of claims 1 to 3, comprising steps of: The raw material preparation steps are in accordance with the chemical formula Ti. 1-x-y M x R y The raw materials for preparing CoSb are prepared by stoichiometry, wherein the M element includes any one of Nb, Ta, Sc and V, the R element includes any one of Zr and Hf, and x is not greater than 0.07 and y is not greater than 0.

25. a sealing step of sealing the raw material in a sealing tube under high vacuum; a heating step of placing the sealing tube into a heating furnace for heating to melt the raw material to form a mixed melt; Crystallization step, the heating furnace is cooled at a set rate to obtain Ti 1-x-y M x R y CoSb single crystal thermoelectric material; In the preparation raw material step, the Sb single metal is added as a fluxing agent in the raw material; the molar ratio of the fluxing agent to the Ti element is 10 to 35 times.

5. The production method according to claim 4, wherein In the heating step, the heating furnace is heated to a set temperature and kept for a set time, wherein the set temperature is 1100℃ to 1150℃; and the set time is 24h to 72h.

6. The production method according to claim 4, wherein The preparation method further comprises a centrifugation step after the crystallization step, the fluxing agent is spun out by a centrifuge, and Ti 1-x-y M x R y CoSb single crystal thermoelectric material.

7. The production method according to claim 4, wherein In the packaging step, air is extracted to achieve a high vacuum sealed environment; the vacuum degree of the high vacuum is lower than 1x10 -3 -1x10 -4 Pa.

8. The production method according to claim 6, wherein In the heating step, the heating furnace is an pit furnace, and the temperature rising speed of the pit furnace is 10 to 15℃ / min; In the crystallization step, the temperature falling speed of the pit furnace is 0.1 to 4℃ / h; In the centrifugation step, the centrifugation temperature of the fluxing agent is 760℃ to 900℃.

9. A thermoelectric device, characterized by, The thermoelectric device has the TiCoSb-based semi-Hasle single crystal thermoelectric material according to any one of claims 1 to 3.

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