Bismuth telluride-based thermoelectric material, preparation method thereof and thermoelectric device

Abstract

The invention discloses a bismuth telluride-based thermoelectric material, a preparation method thereof and a thermoelectric device, and belongs to the technical field of materials. The bismuth telluride-based thermoelectric material comprises a base material, the base material comprises Bi, Te and Se, the general formula of the base material is Bi2Te3-xSex, and x is more than 0 and less than 3; te element is doped in the matrix material and / or a second phase exists in the matrix material, and the second phase is one or more of Se element, MgSe phase and B precipitate. The thermoelectric material prepared by the invention realizes the combination of excellent mechanical properties and thermoelectric properties, and solves the problem of extremely high rejection rate caused by poor mechanical properties of commercial bismuth telluride materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of materials, and particularly relates to a bismuth telluride-based thermoelectric material, a preparation method thereof, and a thermoelectric device. Background Art

[0002] With the exploitation and utilization of fossil energy, the energy crisis has gradually intensified. To achieve sustainable development, the concept of green and clean energy needs to be practiced throughout the entire process of energy development. Based on the above concept, thermoelectric materials have become an indispensable part of industry due to their characteristics such as no mechanical rotating parts, long lifespan, and no pollution. Thermoelectric materials are functional materials that directly convert thermal energy into electrical energy and have also been widely applied in aspects such as aerospace, industrial waste heat, and automotive exhaust waste heat. Their thermoelectric performance mainly depends on the 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. Moreover, the larger the ZT value, the better the thermoelectric performance of the material.

[0003] Currently, the only commercially available thermoelectric material is bismuth telluride (Bi2Te3). Thanks to its narrow bandgap semiconductor, there is still no substitute material at the low-temperature end so far. However, the thermoelectric performance of p-type bismuth telluride material is significantly superior to that of n-type bismuth telluride material, resulting in a mismatch in the performance of n-type and p-type materials when fabricated into thermoelectric devices. At the same time, the ZT value of commercially available p-type bismuth telluride-based materials is ~1.1, while the ZT value of n-type bismuth telluride-based materials is only ~1. Also, compared with p-type materials, the mechanical properties of n-type materials are worse, and the compressive strength is only 30 MPa. This leads to a high probability of defective products in subsequent applications and a significant increase in cost. Therefore, improving the performance of bismuth telluride materials is an urgent challenge. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a bismuth telluride-based thermoelectric material, a preparation method thereof, and a thermoelectric device. The bismuth telluride-based thermoelectric material provided by the present invention has excellent mechanical properties and thermoelectric performance.

[0005] Correspondingly, the present invention also provides a preparation method for the above bismuth telluride-based thermoelectric material.

[0006] The present invention also provides a thermoelectric device comprising the above bismuth telluride-based thermoelectric material.

[0007] To achieve the above purpose, the present invention provides the following solutions:

[0008] A bismuth telluride-based thermoelectric material, the bismuth telluride-based thermoelectric material comprising a matrix material, the matrix material comprising Bi, Te, and Se; doping Te element in the matrix material and / or there being a second phase in the matrix material, the second phase being one or several of Se element, MgSe phase, and B precipitate.

[0009] wherein the structural formula of the matrix material is Bi2Te 3-x Se x , where 0 < x < 3.

[0010] Among them, the bismuth telluride-based thermoelectric material is an n-type bismuth telluride-based thermoelectric material, the Te element is doped in the lattice of the matrix material, and the mass percentage content of the Te element is 0.5% to 2% of the Te element content in the matrix material.

[0011] Among them, the bismuth telluride-based thermoelectric material is an n-type bismuth telluride-based thermoelectric material, the Te element is doped in the lattice of the matrix material, the Se element of the second phase is located at the grain boundary, the MgSe phase of the second phase is located at the grain boundary, the B precipitate of the second phase is dispersed in the matrix material, the mass percentage content of the Te element is 0.5% to 2% of the Te element content in the matrix material, and the addition amount of MgB2 during preparation is not more than 0.5% of the matrix material part.

[0012] Among them, the bismuth telluride-based thermoelectric material is a p-type bismuth telluride-based thermoelectric material, the Se element of the second phase is located at the grain boundary, the MgSe phase of the second phase is located at the grain boundary, the B precipitate of the second phase is dispersed in the matrix material, and the addition amount of MgB2 during preparation is not more than 0.5% of the matrix material part.

[0013] Among them, the grain size of the bismuth telluride-based thermoelectric material is 10~100 μm.

[0014] Among them, the density of the n-type bismuth telluride-based material is about 97%, the thermoelectric figure of merit is 0.89~1.36, the Vickers hardness is 0.4~1.02 GPa, the compressive strength is 55~91 MPa, and the carrier concentration is (0.8~4.5)×10 19 cm -3 , and the mobility is 156~183 cm 2 V -1 S -1 .

[0015] The preparation method of the above-mentioned bismuth telluride-based thermoelectric material includes the following steps:

[0016] S1: Sinter the raw materials to obtain a bismuth telluride-based ingot; the sintering temperature is 800~900 °C, and the heat preservation time is 10~20 h;

[0017] S2: Grind the bismuth telluride-based ingot to obtain a powder;

[0018] S3: Perform hot press sintering on the powder to obtain the bismuth telluride-based material.

[0019] Preferably, the heating rate of the sintering treatment in step S1 is 5-15 °C / min, and after the heat preservation is completed, it is naturally cooled to room temperature.

[0020] Preferably, the sintering in step S1 is carried out in a quartz tube. The specific operation is as follows: under the protection of an inert gas, the raw materials (Bi single element, Te single element, Se single element or MgB2) are placed in the quartz tube; the quartz tube is evacuated to 10 -5 Pa and then sealed; the sealed quartz tube is put into a tube furnace for sintering into an ingot.

[0021] Preferably, the grinding treatment of the bismuth telluride-based ingot in step S2 to obtain powder is carried out in a ball mill under the protection of an inert gas. The ball milling time is 0.5-1 h, and the ball-to-material ratio is (2-5):1. More preferably, step S2 is specifically to take out the bismuth telluride-based ingot from the self-sealing tube and put it into a stainless steel ball milling tank to be ball milled into powder under the protection of an inert gas.

[0022] Preferably, the particle size of the powder obtained in step S2 is 0.1-100 µm.

[0023] Preferably, in step S3, the powder is placed in a graphite mold under the protection of an inert gas, and then the graphite mold is put into a hot press for hot pressing into a block.

[0024] Preferably, in step S3, the pressure of the hot press sintering is 60-90 MPa, the temperature is 530-600 °C, and the heat preservation and pressure holding time is 30 min. Hot press sintering can make the grain growth more complete, the crystallinity better, and thus the mechanical properties better.

[0025] More preferably, the hot press sintering is vacuum hot press sintering, and the vacuum degree is ≤1×10 -1 ~1 Pa.

[0026] Preferably, the inert gas includes argon.

[0027] Among them, the raw materials include a matrix material part and a doping part. The matrix material part includes Bi single element, Te single element and Se single element. The atomic ratio of Bi single element, Te single element and Se single element in the matrix material part is 2:(3-x):x, where 0 < x < 3; the doping part is Te single element, and the addition amount of the Te single element in the doping part is 0.5% to 2% (mass percentage) of the Te element content in the matrix material part;

[0028] Or, the doping part is MgB2, and the addition amount of the MgB2 in the doping part is not more than 0.5% (mass percentage) of the matrix material part;

[0029] Alternatively, the doping part is Te element and MgB2, and the addition amount of Te element in the doping part is 0.5% to 2% of the Te element content in the base material part; the addition amount of MgB2 in the doping part is not more than 0.5% (mass percentage) of the base material part.

[0030] Preferably, the particle size of the added MgB2 is 0.1-10 μm, and preferably the particle size of MgB2 is 0.1-1 μm.

[0031] Preferably, the MgB2 contains 40-60% MgB2, 15-20% Mg, and 30-40% B (mass percentage).

[0032] A thermoelectric device comprises the bismuth telluride-based thermoelectric material.

[0033] The beneficial effects of the present invention are as follows:

[0034] (1) The bismuth telluride-based thermoelectric material prepared in the present invention has excellent thermoelectric properties. 2.7 Se 0.3 +1.5 wt% Te+0.05 wt% MgB2 sample, the conductivity σ at room temperature is ~13×10 4 S / m, the Seebeck coefficient S is ~180µV / k, and the final thermoelectric figure of merit can reach 1.35.

[0035] (2) The bismuth telluride-based thermoelectric material prepared by the present invention has good mechanical properties. The nano-precipitates of B are conducive to the reduction of particle size. This optimization increases the compressive strength and Vickers hardness of the material. In addition, hot pressing sintering can make the grains grow more completely and improve the crystallinity, thereby improving the mechanical properties.

[0036] (3) The thermoelectric material prepared by the present invention realizes a combination of excellent mechanical properties and thermoelectric properties, improving the problem of extremely high scrap rate of commercial bismuth telluride materials due to poor mechanical properties. By optimizing the ball milling and hot pressing processes, the preparation process is greatly shortened. This method has great application potential in subsequent power generation, refrigeration and other fields.

[0037] (4) The method provided by the present invention enables the thermoelectric material to have a wider operating temperature range and at the same time has better thermoelectric performance and mechanical properties, which can ensure a good yield when preparing thermoelectric devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 XRD patterns of n-type bismuth telluride-based thermoelectric materials prepared in Examples 3, 5 to 8 and Comparative Example 1 of the present invention;

[0039] Figure 2Dependency graphs of the conductivity of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1-8 of the present invention versus temperature;

[0040] Figure 3 Dependency graphs of the Seebeck coefficient of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1-8 of the present invention versus temperature;

[0041] Figure 4 Dependency graphs of the carrier concentration of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 2, 3, 5-8 of the present invention versus temperature;

[0042] Figure 5 Dependency graphs of the mobility of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 2, 3, 5-8 of the present invention versus temperature;

[0043] Figure 6 Dependency graphs of the Seebeck coefficient, conductivity, and power factor of the p-type bismuth telluride-based thermoelectric material prepared in Example 9 of the present invention versus temperature;

[0044] Figure 7 Dependency graphs of the power factor of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1-8 of the present invention versus temperature;

[0045] Figure 8 Dependency graphs of the thermal conductivity of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1-8 of the present invention versus temperature;

[0046] Figure 9 Dependency graphs of the thermoelectric figure of merit of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1-8 of the present invention versus temperature;

[0047] Figure 10 Performance graphs of the n-type bismuth telluride-based thermoelectric material prepared in Example 10 of the present invention;

[0048] Figure 11 Vickers hardness graphs of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 3, 5-8 and Comparative Example 1 of the present invention;

[0049] Figure 12 Compressive strength graphs of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 3, 5-8 and Comparative Example 1 of the present invention;

[0050] Figure 13 EBSD graphs of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 3, 5, 8 and Comparative Example 2 of the present invention. Among them Figure 13 a in is the EBSD graph of the bismuth telluride-based thermoelectric material prepared in Example 3, Figure 13 b in is the EBSD graph of the bismuth telluride-based thermoelectric material prepared in Example 5, Figure 13In this, c is the EBSD pattern of the bismuth telluride-based thermoelectric material prepared in Example 8, Figure 13 In this, d is the EBSD pattern of the bismuth telluride-based thermoelectric material prepared in Comparative Example 2;

[0051] Figure 14 This is the SEM pattern of the n-type bismuth telluride-based thermoelectric material prepared in Example 6 of the present invention. Detailed implementation manners

[0052] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various implementation manners of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0053] Unless otherwise specified, the raw materials and equipment used in the present invention are all commercially available products.

[0054] The present invention uses a co-doping method to improve the thermoelectric performance of bismuth telluride-based materials.

[0055] The bismuth telluride-based thermoelectric material prepared by the present invention has excellent thermoelectric performance and high electrical performance. At room temperature, the electrical conductivity σ is 13×10 4 S / m, the Seebeck coefficient S is 180 μV / K. Compared with the undoped sample, it is found that the increase in carrier concentration is due to the entry of Te element into the lattice. At the same time, the addition of MgB2 is beneficial to the increase of the effective mass of carriers. At the same time, since Mg combines with a small amount of Se element in bismuth telluride, a MgSe second phase is formed at the grain boundary, reducing the grain boundary barrier, effectively scattering phonons, and a large number of B-rich nano-precipitates are in the matrix, hindering grain boundary movement. The grain size gradually decreases with the increase of the MgB2 content, which is beneficial to increasing its mechanical properties. The decrease in grain size and the increase in grain boundary number are also beneficial to phonon scattering, thus obtaining an extremely low lattice thermal conductivity. This decoupled method enables the final thermoelectric figure of merit of the material to reach 1.35. The present invention is prepared by a solid-phase sintering process, and the grain size is controlled in the range of 10-100 μm through the grain boundary pinning effect of B element, and the Vickers hardness is increased to 91 HV. Experiments show that the material modified by coordination obtains a peak ZT value of 1.28 at 360 K, which is about 30% higher than that of traditional n-type Bi2Te3. At the same time, the compressive strength reaches 73 MPa, showing excellent thermoelectric conversion efficiency and mechanical reliability.

[0056] In the present invention, additional point defects are introduced by introducing MgB2 to reduce the thermal conductivity. Since the metallicity of Mg element is stronger than that of Bi element, Mg can combine with Se element to form MgSe. The formation of the MgSe second phase is beneficial to phonon scattering, thereby reducing the lattice thermal conductivity. At the same time, B element is beneficial to pinning grain boundaries and reducing grain size, thereby improving the mechanical properties of the material.

[0057] In the present invention, the relative density of the bismuth telluride-based thermoelectric material is about 97%, the thermoelectric figure of merit is 0.89 - 1.35, the Vickers hardness is 0.4 - 1.02 GPa, the compressive strength is 55 - 91 MPa, (0.8 - 4.5)×10 19 cm -3 , the mobility is 156 - 183 cm 2 V -1 S -1 .

[0058] In the present invention, the operations are all carried out in an inert gas. The inert gas is preferably argon. Through the protection of the inert gas, oxidation of the material can be prevented. In the present invention, the purities of the Bi, Sb, and Te elemental substances are preferably >99.99%.

[0059] In the embodiment of the present invention, the sintering treatment in step S1 can be carried out as follows: evacuate the quartz tube to 10 -5 pa, and then seal it at high temperature using a hydrogen-oxygen torch. The sealed quartz tube is placed in a tube furnace for sintering into an ingot. The sintering temperature of the tube furnace is 800 - 900 °C, the heating rate is 5 - 15 °C / min, keep the temperature for 10 - 20 h, and then cool it naturally to room temperature.

[0060] In the embodiment of the present invention, step S2 is specifically to take out the bismuth telluride-based ingot from the self-sealing tube, and ball mill it into powder in a stainless steel ball milling tank under the protection of an inert gas. The particle size of the powder is 0.1 - 100 µm. The ball milling time is 0.5 - 1 h, and the ball-to-material ratio is (2 - 5):1.

[0061] In the embodiment of the present invention, step S3 is specifically to put the powder into a graphite mold with a diameter of 12.7 mm under the protection of an inert gas, and then put the graphite mold into a hot press for hot pressing into a block. The pressure of the hot press sintering is 60 - 90 MPa, the temperature is 530 - 600 °C, and the holding time under pressure is 30 min. The hot press sintering is vacuum hot press sintering, and the vacuum degree ≤ 1×10 -1 ~1 Pa. The inert gas includes argon. The diameter of the graphite mold is 12.7 - 12.8 mm. 2.5 - 3.5 g of bismuth telluride-based powder is loaded into the graphite mold.

[0062] The bismuth telluride thermoelectric material prepared by the present invention realizes the combination of excellent mechanical properties and thermoelectric properties, improves the problem of extremely high rejection rate caused by poor mechanical properties of commercial bismuth telluride materials, and matches the properties of n-type and p-type materials. Moreover, the method has a short cycle and has great application potential in subsequent fields such as power generation and refrigeration.

[0063] The method provided by the present invention enables the thermoelectric material to have a wide operating temperature range, and at the same time has excellent thermoelectric and mechanical properties, which can ensure a good yield when manufacturing thermoelectric devices.

[0064] The present invention can shorten the time of ball milling and hot press sintering as much as possible to meet the needs of industrial production. The preparation method provided by the present invention is simple to operate, convenient to prepare, has good repeatability, can prepare bismuth telluride-based materials in large quantities, and requires simple equipment.

[0065] The present invention provides the application of the above-mentioned n-type bismuth telluride-based material in thermoelectric devices.

[0066] In order to further illustrate the present invention, the following describes in detail a p-type bismuth telluride-based material, its preparation method and application provided by the present invention with reference to the accompanying drawings and embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0067] Example 1

[0068] A preparation method of a bismuth telluride-based thermoelectric material is as follows:

[0069] S1: Preparation of Bi2Te 2.7 Se 0.3 +0.5 wt% Te powder: Under an inert gas Ar atmosphere, 5.3164 g of Bi element, 4.4042 g of Te element and 0.3013 g of Se element are loaded into a quartz tube, and then the quartz tube is sealed with a hydrogen-oxygen flame. The sealed quartz tube is transferred to a tube furnace, and the tube furnace is heated to 800 °C at a heating rate of 10 °C / s, held for 10 h, and then cooled naturally. Among them, the matrix material part in the raw materials is specifically 5.3164 g of Bi element, 4.3823 g of Te element and 0.3013 g of Se element, and the doping part is 0.0219 g of Te element.

[0070] S2: The fired ingot is placed in a stainless steel ball milling jar with 8 balls (the total weight of the balls is about 30 g) under an inert gas Ar atmosphere, and placed in a ball mill for ball milling for 1 h. The ball milling speed is set at 1200 rpm and the power is 110 W to obtain powder. The powder is cooled, and then the powder is taken out in a glove box to obtain n-type bismuth telluride-based powder;

[0071] S3: Bi2Te 2.7 Se0.3 Preparation of +0.5 wt% Te bulk material: The n-type bismuth telluride-based powder is loaded into a graphite mold with a diameter of 12.7 mm in a glove box. After ensuring that the upper and lower surfaces are flat, it is placed in a hot press for hot pressing and sintering. The pressure is 80 MPa, the temperature is 570 °C, the holding time under pressure is 30 min, and the vacuum degree is 1×10 -1 ~1 Pa. After cooling, the n-type bismuth telluride-based thermoelectric material is obtained.

[0072] What is obtained in this example is an n-type bismuth telluride-based thermoelectric material.

[0073] Example 2

[0074] Bi2Te 2.7 Se 0.3 Preparation of +1 wt% Te: The preparation method is the same as that in Example 1, and the matrix material part in the raw materials is the same. The only difference is that the added amount of doped Te element is 0.0438 g, that is, the total added amount of Te element is 4.426 g.

[0075] What is obtained in this example is an n-type bismuth telluride-based thermoelectric material.

[0076] Example 3

[0077] Bi2Te 2.7 Se 0.3 Preparation of +1.5 wt% Te: The preparation method is the same as that in Example 1, and the matrix material part in the raw materials is the same. The only difference is that the added amount of doped Te element is 0.0657 g, that is, the total added amount of Te element is 4.448 g.

[0078] What is obtained in this example is an n-type bismuth telluride-based thermoelectric material.

[0079] Example 4

[0080] Bi2Te 2.7 Se 0.3 Preparation of +2 wt% Te: The preparation method is the same as that in Example 1, and the matrix material part in the raw materials is the same. The only difference is that the added amount of doped Te element is 0.0876 g, that is, the total added amount of Te element is 4.4699 g.

[0081] What is obtained in this example is an n-type bismuth telluride-based thermoelectric material.

[0082] Examples 1 to 4 are based on the matrix material Bi2Te 2.7 Se 0.3Te element is doped in the matrix. The present invention improves the thermoelectric properties of the material by introducing Te element (electronegativity 2.1) with a smaller electronegativity difference than Bi element (electronegativity 2.02). The small electronegativity difference can make the Te element in the matrix have a greater solubility, thereby improving the carrier concentration of the material (Te element doping mainly optimizes the carrier concentration). The increase in carrier concentration will increase the electrical conductivity, thereby improving the thermoelectric performance.

[0083] Example 5

[0084] Bi2Te 2.7 Se 0.3 Preparation of +1.5 wt%Te+0.025wt% MgB2: The preparation method is the same as that of Example 3, except that the doping part also includes 0.0025g of MgB2. The MgB2 used in this example is homemade in the laboratory. That is to say, the doping part in this example includes 0.0657g of Te element and 0.0025g of MgB2.

[0085] The obtained material in this embodiment is an n-type bismuth telluride-based thermoelectric material.

[0086] MgB2 was prepared by the following method: a mixture of MgB2, Mg and B powder was prepared by using β-MgBH4 (purchased from Peking University) at 450-600°C in a tube furnace for 1 hour. The obtained product was ground into powder using a grinding pestle. The obtained MgB2 contained 40-60% MgB2, 15-20% Mg, and 30-40% B, and the particle size of the obtained MgB2 was 0.1-1 μm.

[0087] The inventors found that MgB2 decomposes Mg and B at high temperatures. Since the size of Mg in the homemade MgB2 is smaller, the activity of Mg is higher. Mg can react with Se to generate MgSe. The precipitation of MgSe at the grain boundary is conducive to passivation of the grain boundary, and it physically covers the grain boundary to reduce the defect density at the grain boundary. The B element has the effect of pinning the grain boundary, reducing the grain size, thereby increasing the mechanical properties. Under this optimization, the compressive strength and Vickers hardness of the material are increased. The nanocomposite of B effectively scatters phonons, thereby reducing thermal conductivity. The advantage of using a mixture compared to commercial MgB2 is that the diffusion rate of the compound is weaker than that of the single substance, which leads to uneven doping of the material during the reaction process, and the saturated vapor pressure of Mg at high temperature is relatively small, which makes Mg very easy to volatilize. Additional Mg single substance can also supplement the volatilization of Mg.

[0088] Example 6

[0089] Bi2Te 2.7 Se 0.3Preparation of +1.5 wt% Te + 0.05 wt% MgB₂: The preparation method is the same as that of Example 3, except that the amount of MgB₂ added is 0.005 g. The MgB₂ used in this example is self-made in the laboratory. The doping part in this example includes 0.0657 g of Te element and 0.005 g of MgB₂.

[0090] The n-type bismuth telluride-based thermoelectric material is obtained in this example.

[0091] Example 7

[0092] Bi2Te 2.7 Se 0.3 Preparation of +1.5 wt% Te + 0.075 wt% MgB₂: The preparation method is the same as that of Example 3, except that the amount of MgB₂ added is 0.0075 g. The MgB₂ used in this example is self-made in the laboratory. The doping part in this example includes 0.0657 g of Te element and 0.0075 g of MgB₂.

[0093] The n-type bismuth telluride-based thermoelectric material is obtained in this example.

[0094] Example 8

[0095] Bi2Te 2.7 Se 0.3 Preparation of +1.5 wt% Te + 0.1 wt% MgB₂: The preparation method is the same as that of Example 3, except that the amount of MgB₂ added is 0.01 g. The MgB₂ used in this example is self-made in the laboratory. The doping part in this example includes 0.0657 g of Te element and 0.01 g of MgB₂.

[0096] The n-type bismuth telluride-based thermoelectric material is obtained in this example.

[0097] Examples 5 to 8 adopt a dual synergistic modification strategy: First, the carrier concentration is regulated by isoelectronic doping of Te element (electronegativity difference Δχ = 0.08) to increase the conductivity to 1.3×10 5 S / m; Secondly, the self-synthesized MgB₂ composite phase is introduced to form high-density nano-defects (size <50 nm) in the matrix, reducing the lattice thermal conductivity to 0.36 W / mK.

[0098] Example 9

[0099] Bi2Te 2.7 Se 0.3Preparation of +0.05 wt% MgB2: The preparation method is the same as that of Example 1, except that 4.3823 g of element Te is added and the addition amount of MgB2 is 0.005 g. In this example, the doping part is 0.005 g of MgB2. The MgB2 in this example is commercially available.

[0100] The p-type bismuth telluride-based thermoelectric material is obtained in this example.

[0101] Example 10

[0102] Preparation of Bi2Te2Se + 1.5 wt% Te + 0.05 wt% MgB2: The preparation method is the same as that of Example 1, except that 5.556 g of element Bi, 3.444 g of Te and 1.051 g of Se are added, and the addition amount of MgB2 is 0.005 g. In this example, the doping part is 0.05 g of Te and 0.005 g of MgB2.

[0103] The n-type bismuth telluride-based thermoelectric material is obtained in this example.

[0104] Comparative Example 1

[0105] Bi2Te 2.7 Se 0.3 Preparation: The preparation method is the same as that of Example 1, except that the addition amount of Te element is 4.3823 g.

[0106] Comparative Example 2

[0107] Bi2Te 2.7 Se 0.3 +1.5 wt%Te + 0.5wt% MgB2 Preparation: The preparation method is the same as that of Example 3, except that the addition amount of a small amount of MgB2 is 0.05 g. In this example, the doping part includes 0.0657 g of Te element and 0.05 g of MgB2.

[0108] Performance Test and Structure Characterization

[0109] Figure 1 This is the XRD pattern of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 3, 5 - 8 and Comparative Example 1 of the present invention. As Figure 1 shown, the diffraction peaks of all samples correspond to the PDF cards, showing a high-purity phase.

[0110] Figure 2 This is the dependence map of the conductivity on temperature of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1 - 8 of the present invention. As Figure 2 shown, at room temperature of 300 K, the curve of the conductivity σ varying with the content of additional Te and MgB2, when x = 0.5, σ = 4.8×104 S / m, when x = 1, σ = 8.6×10 4 S / m, when x = 1.5, σ = 12.6×10 4 S / m, when x = 2, σ = 13.8×10 4 S / m, when x = 1.5 and y = 0.025, σ = 13×10 4 S / m, when x = 1.5 and y = 0.05, σ = 12.9×10 4 S / m, when x = 1.5 and y = 0.075, σ = 10.7×10 4 S / m, when x = 1.5 and y = 0.1, σ = 8.5×10 4 When it is S / m, it shows that the n-type bismuth telluride-based thermoelectric material prepared by the present invention has a relatively high electrical conductivity. As the Te content increases to x = 2, the increase in electrical conductivity is not obvious, indicating that it reaches saturation. Subsequently, adding a small amount of MgB2 is beneficial to further improving its electrical properties.

[0111] Figure 3 It is the dependence map of the Seebeck coefficient of the n-type bismuth telluride-based thermoelectric material prepared in Examples 1 - 8 of the present invention on temperature. As Figure 3 shown, at room temperature of 300K, the variation curves of the Seebeck coefficient S with the content of additional Te and MgB2. When x = 0.5, S = -217.3µV / k; when x = 1, S = -182.1µV / k; when x = 1.5, S = -167.1µV / km; when x = 2, S = -153.4µV / k; when x = 1.5 and y = 0.025, S = -173.3µV / k; when x = 1.5 and y = 0.05, S = -179.1µV / k; when x = 1.5 and y = 0.075, S = -188.5µV / k; when x = 1.5 and y = 0.1, S = -203.7µV / k. Since the electrical conductivity and the Seebeck coefficient are in a mutually coupled relationship, the increase in electrical conductivity will inevitably affect the loss of the Seebeck coefficient. As the Te element increases, the Seebeck coefficient gradually decreases, while after adding a small amount of MgB2, the Seebeck coefficient increases again. The main reason is that MgB2 effectively increases the grain boundary potential barrier, resulting in a decrease in electrical conductivity.

[0112] Figure 4 It is the dependence map of the carrier concentration of the n-type bismuth telluride-based thermoelectric material prepared in Examples 2, 3, 5 - 8 of the present invention on temperature. As Figure 4 shown, at room temperature of 300K, the variation curves of the carrier concentration n with the increase of the content of additional Te and MgB2, x and y. When x = 1, n H = 2.8×10 19 cm -1 When x = 1.5, n H = 4.2×10 19 cm-1 When x = 1.5 and y = 0.025, n H = 4.3×10 19 cm -1 (The optimal carrier concentration of bismuth telluride material is usually around 5×10 19 cm -1 ). When x = 1.5 and y = 0.05, n H = 3.9×10 19 cm -1 When x = 1.5 and y = 0.075, n H = 3.6×10 19 cm -1 When x = 1.5 and y = 0.1, n H = 3.45×10 19 cm -1 . Since the conductivity is positively correlated with the carrier concentration, the increase in the carrier concentration will inevitably increase the conductivity. This also corresponds to Figure 2 the corresponding increase in conductivity with the increase of the additional Te content in

[0113] Figure 5 Figure 35 shows the dependence of the mobility μ of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 2, 3, 5 to 8 of the present invention on temperature. As H shown, at room temperature of 300K, the mobility μ Figure 5 increases with the increase of the additional Te content x. When x = 1, μ H = 158.6 cm H V 2 s -1 When x = 1.5, μ -1 = 169.9 cm H V 2 s -1 When x = 1.5 and y = 0.025, μ -1 = 171 cm H V 2 s -1 (The optimal carrier concentration of bismuth telluride material is usually around 5×10 -1 cm 19 ). When x = 1.5 and y = 0.05, μ -1 = 182.2 cm H V 2 s -1 When x = 1.5 and y = 0.075, μ -1 = 158.6 cm H V 2 s -1 When x = 1.5 and y = 0.1, μ -1 = 160.5 cm H = 160.5 cm2 V -1 s -1 Since the conductivity is positively correlated with the carrier concentration, an increase in the carrier concentration will necessarily increase the conductivity. This also corresponds to Figure 2 the corresponding increase in conductivity with the increase of the additional Te content in. Then MgB2 is added. When a small amount is added, the carrier concentration changes little, while the mobility increases rapidly. The main reason is the reduction of the interface barrier, resulting in an increase in mobility. Then the mobility decreases because the grain size decreases and the grain boundaries increase, hindering the movement of carriers.

[0114] Figure 6 The dependence spectra of the Seebeck coefficient S, conductivity σ, and power factor PF of the p-type bismuth telluride-based thermoelectric material prepared in Example 9 of the present invention on temperature. As Figure 6 shown, it is found that adding a small amount of MgB2 converts the n-type bismuth telluride material into a p-type, indicating that MgB2 changes the carrier type. The main reason is that MgB2 reacts with Se to form MgSe, and there are many Se vacancies in the material. If no additional Te element is introduced, the loss of Se vacancies will greatly increase the vacancy concentration, resulting in a change from n-type to p-type material. Since the conductivity and the Seebeck coefficient are coupled, an increase in conductivity will necessarily affect the loss of the Seebeck coefficient. As the Te element increases, the Seebeck coefficient gradually decreases, and after adding a small amount of MgB2, the Seebeck coefficient increases again. The main reason is that MgB2 effectively increases the grain boundary barrier, resulting in a decrease in conductivity.

[0115] Figure 7 The dependence spectrum of the power factor of the n-type bismuth telluride-based thermoelectric material prepared in Examples 1-8 of the present invention on temperature. As Figure 6 shown, at room temperature of 300 K, the power factor PF continuously increases with the increase of the Bi content. When x = 0.5 , when x = 1 , when x = 1.5 , when x = 2 , when x = 1.5 y = 0.025 , when x = 1.5 y = 0.05 , when x = 1.5 y = 0.075 , when x = 1.5 y = 0.15 . As the additional Te content x increases, PF gradually increases, especially more significantly at room temperature, until it reaches the maximum value at x = 1.5. On the basis of x = 1.5, continuing to add MgB2, MgB2 helps to improve the mobility of the material, the mobility increases greatly, and effectively optimizes the thermoelectric performance of the material.

[0116] Figure 8This is the graph of the temperature dependence of the thermal conductivity of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1-8 of the present invention. As Figure 6 shown, at room temperature of 300 K, the thermal conductivity κ (referring to the total thermal conductivity) first increases and then decreases with the increase of the additional Bi content x. When x = 0.5 , when x = 1 , when x = 1.5 , when x = 2 , when x = 1.5 y = 0.025 , when x = 1.5 y = 0.05 , when x = 1.5 y = 0.05 , when x = 1.5 y = 0.05 . The thermal conductivity mainly includes electronic thermal conductivity, lattice thermal conductivity, and bipolar heat conduction. The increase in thermal conductivity with the increase of Te content is mainly attributed to the increase in electronic thermal conductivity, because the electronic thermal conductivity is mainly proportional to the electrical conductivity, and the continuous increase in electrical conductivity makes a huge contribution to the thermal conductivity. Subsequently, the addition of a small amount of MgB2 reduces the thermal conductivity due to the formation of MgSe and the enhanced phonon scattering caused by the increase in the number of grain boundaries, thereby reducing the lattice thermal conductivity.

[0117] Figure 9 This is the graph of the temperature dependence of the thermoelectric figure of merit of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 1-8 of the present invention. Based on the above test results of electrical conductivity, Seebeck coefficient, and thermal conductivity, the thermoelectric figure of merit ZT is calculated. The maximum ZT value is obtained when the additional Te element is added until x = 1.5. Then, by adding a small amount of MgB2, the lattice thermal conductivity and electrical properties of the material are further optimized. When x = 1.5 y = 0.05, the maximum ZT value is 1.28. This shows that the additional Te element effectively increases the carrier concentration of the material, and the subsequent MgB2 effectively improves the thermal properties of the material.

[0118] Figure 10 This is the performance graph of the n-type bismuth telluride-based thermoelectric materials with other components prepared in Example 10 of the present invention. As Figure 10 shown, when the matrix material is selected as Bi2Te2Se and 1.5 wt% Te and 0.05 wt% MgB2 are added in the same way, the performance of the material is significantly optimized. Therefore, it shows that this method is still applicable to the materials of other components Bi2Te （3-x） Se x .

[0119] Figure 11 This is the Vickers hardness graph of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 3, 5-8 and Comparative Example 1 of the present invention; as Figure 11As shown, the Vickers hardness first increases and then decreases with the increase of Bi content. After seven tests, when x = 0, Hv = 0.35 - 0.42 GPa; when x = 1.5, Hv = 0.47 - 0.54 GPa; when x = 1.5 and y = 0.025, Hv = 0.66 - 0.77 GPa; when x = 1.5 and y = 0.05, Hv = 0.7 - 0.8 GPa; when x = 1.5 and y = 0.075, Hv = 0.77 - 0.85 GPa; and when x = 1.5 and y = 0.1, Hv = 0.93 - 1.01 GPa. The test average values are listed in Table 1. The increase in Vickers hardness is mainly attributed to the fact that the introduction of Bi helps to increase the density.

[0120] Figure 12 This is the compressive strength spectrum of the n-type bismuth telluride-based thermoelectric materials prepared in Examples 3, 5 - 8 and Comparative Example 1 of the present invention. As Figure 12 shown, the compressive strength gradually increases with the increase of Te and MgB2 content. When x = 0, the compressive strength is 56 - 60 MPa; when x = 1.5, the compressive strength is 56 - 60 MPa; when x = 1.5 and y = 0.025, the compressive strength is 70 - 72 MPa; when x = 1.5 and y = 0.05, the compressive strength is 72 - 75 MPa; when x = 1.5 and y = 0.025, the compressive strength is 76 - 78 MPa; when x = 1.5 and y = 0.1, the compressive strength is 82 - 85 MPa. The test average values are listed in Table 1. The increase in Vickers hardness is mainly attributed to the fact that the introduction of B helps to hinder the movement of grain boundaries.

[0121] Figure 13 This is the EBSD spectrum of the bismuth telluride-based thermoelectric materials of Examples 3, 5, 8 and Comparative Example 2 of the present invention. Among them Figure 13 a is the EBSD spectrum of the bismuth telluride-based thermoelectric material prepared in Example 3, Figure 13 b is the EBSD spectrum of the bismuth telluride-based thermoelectric material prepared in Example 5, Figure 13 c is the EBSD spectrum of the bismuth telluride-based thermoelectric material prepared in Example 8, Figure 13 d is the EBSD spectrum of the bismuth telluride-based thermoelectric material prepared in Comparative Example 2. It can be seen from Figure 13 that with the increase of MgB2 content, the grain size decreases, corresponding to the increase in Vickers hardness and compressive strength. It should be noted that when an additional 0.5% content of MgB2 is added, a huge change occurs in the grain size.

[0122] Figure 14 This is the SEM spectrum of the n-type bismuth telluride-based thermoelectric material Bi2Te 2.7 Se 0.3 +1.5 wt% Te + 0.05 wt% MgB2 prepared in Example 6 of the present invention. From Figure 14As can be seen, we observed the precipitation of MgSe at the grain boundaries. These precipitates have a certain scattering effect on the carriers, resulting in a decrease in thermal conductivity.

[0123] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

[0124] The parts not elaborated in detail in the specification of the present invention belong to the well-known technology in the art. The above embodiments are provided only for the purpose of describing the present invention and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims. All equivalent replacements and modifications made without departing from the spirit and principles of the present invention shall be covered within the scope of the present invention.

Claims

1. A bismuth telluride-based thermoelectric material, characterized in that, The bismuth telluride-based thermoelectric material includes a matrix material, the matrix material includes Bi, Te, and Se, and the general formula of the matrix material is Bi2Te 3-x Se x， where 0 < x < 3; Doping Te element in the matrix material and / or there is a second phase in the matrix material, and the second phase is one or more of Se element, MgSe phase and B precipitate.

2. The bismuth telluride-based thermoelectric material according to claim 1, characterized in that, The bismuth telluride-based thermoelectric material is an n-type bismuth telluride-based thermoelectric material. The Te element is doped in the lattice of the matrix material, and the mass percentage of the Te element is 0.5% to 2% of the Te element content in the matrix material.

3. The bismuth telluride-based thermoelectric material according to claim 1, characterized in that, The bismuth telluride-based thermoelectric material is an n-type bismuth telluride-based thermoelectric material. The Te element is doped in the lattice of the matrix material. The Se element of the second phase is located at the grain boundary, the MgSe phase of the second phase is located at the grain boundary, and the B precipitate of the second phase is dispersed in the matrix material.

4. The bismuth telluride-based thermoelectric material according to claim 1, characterized in that, The bismuth telluride-based thermoelectric material is a p-type bismuth telluride-based thermoelectric material. The Se element of the second phase is located at the grain boundary, the MgSe phase of the second phase is located at the grain boundary, and the B precipitate of the second phase is dispersed in the matrix material.

5. The preparation method of the bismuth telluride-based thermoelectric material according to any one of claims 1 to 4, characterized in that, The preparation method includes the following steps: Sintering the raw materials to obtain a bismuth telluride-based ingot; the sintering temperature is 800~900 °C, and the heat preservation time is 10~20 h; Grinding the bismuth telluride-based ingot to obtain a powder; Performing hot pressing sintering treatment on the powder to obtain the bismuth telluride-based material.

6. The preparation method of the bismuth telluride-based thermoelectric material according to claim 5, characterized in that, The raw materials include a matrix material part and a doping part. The matrix material part includes Bi element, Te element and Se element. The atomic ratio of Bi element, Te element and Se element in the matrix material part is 2:(3 - x):x, where 0 < x < 3; The doping part is Te element, and the addition amount of Te element in the doping part is 0.5% to 2% of the Te element content in the matrix material part; or, the doping part is MgB2, and the addition amount of MgB2 in the doping part is not more than 0.5% of the matrix material part; or, the doping part is Te element and MgB2, the addition amount of Te element in the doping part is 0.5% to 2% of the Te element content in the matrix material part; the addition amount of MgB2 in the doping part is not more than 0.5% of the matrix material part.

7. The preparation method of the bismuth telluride-based thermoelectric material according to claim 5, characterized in that, The pressure of the hot pressing sintering treatment is 60~90 MPa, the temperature is 500~650 °C, and the heat preservation and pressure holding time is 20~40 min.

8. The preparation method of the bismuth telluride-based thermoelectric material according to claim 5, characterized in that, The particle size of the powder is 0.1~100 µm.

9. The preparation method of the bismuth telluride-based thermoelectric material according to claim 6, characterized in that, The MgB2 contains 40~60% of MgB2, 15~20% of Mg, and 30~40% of B; And / or, the particle size of MgB2 is 0.1~1 µm.

10. A thermoelectric device, characterized in that, Including the bismuth telluride-based thermoelectric material according to any one of claims 1 to 4.

Images