Preparation method of bismuth telluride-based thermoelectric material

Abstract

The invention discloses a bismuth telluride-based thermoelectric material preparation method, which comprises the steps of S1, weighing high-purity Bi, Te and Sb elementary substance powder as raw materials according to a P-type bismuth telluride thermoelectric material chemical formula (Bi1-ySby) 2Te3; s2, pouring the uniformly mixed materials into a quartz crucible, placing the quartz crucible in a closed atmosphere furnace, introducing protective gas into the furnace, and inserting a fixed stirring paddle; raising the temperature of the atmosphere furnace constantly, lowering a stirring paddle for forced stirring after reaching a set temperature, raising the stirring paddle after constant-temperature intensified smelting for a period of time, and taking out a product after cooling the product to room temperature along with the furnace; and S3, uniformly refining the product obtained in the step S2 into powder, filling the powder into a mold, compacting and sintering to obtain the high-performance bismuth telluride-based thermoelectric material. The bismuth telluride-based thermoelectric material prepared through the method is more uniform in alloy component, smaller in grain size and more excellent in thermoelectric performance, and compared with a traditional zone melting method and a smelting-annealing method, the method is easy to operate, simple and convenient in process and suitable for large-scale commercial production.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric material preparation technology, and in particular to a method for preparing bismuth telluride-based thermoelectric materials. Background Technology

[0002] Thermoelectric materials, due to their Seebeck and Peltier effects, enable the direct conversion between heat and electrical energy, and are widely used in waste heat recovery, solid-state refrigeration, thermoelectric power generation, and thermoelectric cooling, such as in semiconductor lasers, 5G communication equipment, cryogenic medical devices, and household refrigerators. Among many thermoelectric materials, bismuth telluride and its alloys exhibit excellent thermoelectric performance in the room temperature range and are currently the most commercially available thermoelectric materials. Based on the different doping elements, bismuth telluride-based materials can be divided into two main categories: P-type and N-type. P-type materials are mainly doped with a small amount of Sb, while N-type materials are doped with Se.

[0003] Traditional preparation of bismuth telluride-based materials often employs a melting-annealing method, mainly including two key steps: vacuum high-temperature melting and long-term annealing. Typically, high-purity metals Bi, Te, Sb, or Se (purity reaching 4N or higher) are precisely weighed according to the target stoichiometric ratio, placed in a quartz tube, and evacuated to 10 °C. -3 Below Pa, the material is then smelted at 700°C to 900°C to fully alloy the various metallic elements into a melt. After smelting, it is quenched with liquid nitrogen or ice water, and finally annealed for a long time at 400°C to 500°C to obtain a homogeneous bismuth telluride material. This process is relatively mature, requires simple equipment, and is suitable for large-scale mass production. However, this method still suffers from compositional segregation caused by slow cooling rates, resulting in larger grains that affect the overall performance of the device.

[0004] Traditional methods for preparing bismuth telluride-based materials suffer from insufficient mechanical strength, significant anisotropy in thermoelectric properties, and limited ZT values. Many scholars and researchers have subsequently developed new technologies such as mechanical alloying, solvothermal methods, rapid densification, and zone melting. Mechanical alloying involves placing high-purity elemental or pre-alloyed powders along with grinding balls into a high-energy ball mill jar. During ball milling, the metal powder undergoes repeated cold welding, fracture, and recombination, ultimately achieving atomic-level alloying in the solid state. This process enhances phonon scattering through the nanograin boundaries formed during ball milling, significantly reducing lattice thermal conductivity. Simultaneously, mechanical alloying avoids the high-temperature melting process, effectively suppressing the loss of volatile elements and facilitating precise control of chemical composition. However, prolonged mechanical ball milling can lead to grinding ball breakage, introducing impurities. The solvothermal method is a solution chemistry approach that directly synthesizes bismuth telluride nanoparticles in an autoclave by dissolving bismuth (BiCl3) and tellurium (TeO2 or Te) in a specialized solvent. This process allows for precise control of the product's morphology and structure, and these low-dimensional nanostructures possess abundant interfaces, providing more phonon scattering sites. However, this method is limited by low yield, high cost, and complex subsequent powder collection and processing. Rapid densification technology is currently the most mainstream method for preparing thermoelectric materials. It densifies the powder using spark plasma sintering and hot pressing sintering techniques. This rapid sintering method effectively inhibits grain growth and preserves the original powder nanostructure. Hot pressing sintering equipment is relatively simple, using an external heater combined with unidirectional pressure for powder densification. This ensures that the obtained material has high density while maximizing the preservation of the original nanostructure.

[0005] To address the problems existing in the above technologies and considering the advantages and disadvantages of each process, this paper proposes a simple and mass-producible method for preparing high-performance bismuth telluride-based thermoelectric materials, providing a new direction for the large-scale production of commercial bismuth telluride-based thermoelectric materials. Summary of the Invention

[0006] The purpose of this application is to provide a method for preparing bismuth telluride-based thermoelectric materials, so as to solve the problems of poor device performance caused by component segregation and large grain size in current bismuth telluride thermoelectric materials.

[0007] To achieve the above objectives, this application provides the following technical solution: a method for preparing bismuth telluride-based thermoelectric materials, the specific steps of which are as follows:

[0008] S1, according to the chemical formula Bi2Te of N-type bismuth telluride thermoelectric material 3-x Se x， Weigh high-purity Bi, Te, and Se elemental powders as raw materials, where 0.1 ≤ x ≤ 0.25, or according to the chemical formula of p-type bismuth telluride thermoelectric material (Bi 1-y Sb y)2Te3, where 0.7≤ y≤0.9, high-purity Bi, Te and Sb elemental powders are weighed as raw materials.

[0009] S2. After uniform mixing, the material is poured into a quartz crucible and placed in a sealed atmosphere furnace. A protective gas is introduced into the furnace, and a fixed stirring paddle is inserted. The atmosphere furnace is heated, with a heating rate of 20°C~25°C / min in the range of room temperature to 400°C. The temperature is then held at 400°C for 30 minutes. At this time, the stirring paddle is lowered for forced stirring at a speed of 40 r~50 r / min. Subsequently, the heating rate is 10°C~15°C / min in the range of 400°C~900°C. When the temperature reaches the set temperature of 800°C~900°C, stirring is continued for 120 minutes. The heating source is then turned off, and the stirring paddle is kept rotating at 20 r~25 r / min. The furnace temperature is lowered to 600°C at a cooling rate of 10°C~15°C / min. The stirring paddle is then raised. During this process, the composition is further homogenized by the convection of the melt itself. The product is then slowly cooled to room temperature at a rate of 6°C / min and then removed.

[0010] The beneficial effects of a heating rate of 20°C~25°C / min within the range of room temperature to 400°C:

[0011] Bi has a melting point of about 271°C, and Te has a melting point of about 452°C. The main melting stage of Bi is in the range of room temperature to 400°C. The heating rate of 20°C to 25°C combines efficiency and uniformity.

[0012] If the rate is too high (e.g., >25°C / min), it will cause an excessive temperature difference between the top and bottom of the crucible. The Bi at the bottom will not melt while the top is already overheated, which can easily cause local molten splashing.

[0013] Too low a rate (e.g., <20°C / min) will prolong the preheating time and increase the risk of Bi oxidation at low temperatures (although there is a protective gas, there is still a possibility of trace oxidation after long-term exposure).

[0014] A melting rate of 20°C to 25°C / min allows Bi to melt rapidly and uniformly into a liquid substrate, creating a uniform melt environment for the subsequent dissolution of Te, Sb, or Se, and preventing localized accumulation of subsequent elements due to uneven Bi melting.

[0015] The beneficial effects of holding at 400°C for 30 minutes and stirring at a speed of 40~50 r / min:

[0016] 400°C is close to the melting point of Te (452°C). At this point, Te begins to soften and gradually dissolves in liquid Bi. A 30-minute holding time allows Te to complete the initial dissolution-diffusion process, avoiding direct heating that would cause undissolved Te to enter the high-temperature zone, forming undissolved Te particles that are difficult to eliminate later and would cause component segregation.

[0017] The heat preservation process can balance the temperature field inside the crucible, eliminate the local temperature difference generated during the heating stage, and provide a stable temperature basis for subsequent uniform heating.

[0018] Excessive rotation speed (e.g., >50 r / min) can cause the melt to splash against the crucible wall due to centrifugal force, resulting in element loss (especially Te and Se). At the same time, excessive shear force of the stirring paddle can easily cause melt turbulence, producing residual bubbles, which can lead to porosity in the final material and reduce mechanical strength.

[0019] If the rotation speed is too low (e.g., <40 r / min), the stirring force will be insufficient, which will not be able to break the local aggregation of Te in the Bi melt, and will easily form Te enrichment areas, resulting in uneven composition.

[0020] A rotation speed of 40 r~50 r / min can form stable melt convection, uniformly dispersing the initially dissolved Te into the Bi melt, while avoiding splashing and bubble generation, laying a uniform foundation for subsequent all-element alloying.

[0021] The beneficial effects of raising the furnace temperature from 400°C to 800°C~900°C at a rate of 10°C~15°C / min:

[0022] The temperature range of 400°C to 900°C is the stage of complete dissolution of Te, dissolution of Sb or Se, and alloying of all elements (Sb has a melting point of about 630°C, and Se has a melting point of about 221°C, but Se needs to be at a high temperature to stably dissolve in Bi-Te melt).

[0023] If the rate is too high (e.g., >15°C / min), Te will not be completely dissolved before entering the high-temperature zone. At the same time, the dissolution rate of Sb or Se cannot keep up with the heating rate, which easily forms island-like undissolved particles. These particles are difficult to eliminate during subsequent heat preservation, resulting in microscopic component segregation.

[0024] Too low a rate (e.g., <10°C / min) will prolong the high-temperature exposure time and increase the volatilization loss of Te and Se (Te volatilization rate increases significantly above 800°C, and Se is more easily volatilized), resulting in the Te and Se content in the alloy being lower than the design value, affecting thermoelectric properties (e.g., a decrease in ZT value).

[0025] A heating rate of 10°C~15°C / min allows Te, Sb, or Se to gradually and completely dissolve as the temperature rises. At the same time, the atomic diffusion rate is matched with the heating rate to ensure that each element is evenly distributed in the melt and to avoid compositional inhomogeneity caused by dissolution lag.

[0026] The beneficial effects of maintaining stirring at 40-50 rpm for 120 minutes after the furnace temperature reaches 800°C~900°C are as follows:

[0027] This temperature range represents the full alloying temperature window for bismuth telluride-based alloys: below 800°C, Sb or Se cannot diffuse sufficiently into the Bi-Te lattice, easily forming a second phase, leading to enhanced carrier scattering and reduced conductivity; above 900°C, the volatilization loss of Te and Se increases dramatically (Te has a vapor pressure of approximately 133 Pa at 900°C, and Se has an even higher vapor pressure), causing the alloy chemical formula to deviate significantly from the design value, while the melt viscosity decreases, increasing the risk of splashing during stirring; 800°C~900°C ensures that Bi, Te, Sb, or Se completely form a homogeneous solid solution, with element volatilization controlled at <0.5%, balancing alloying sufficiency and compositional stability.

[0028] Too short a stirring time will result in insufficient atomic diffusion and uneven distribution of Sb or Se in the crystal lattice (such as local Sb enrichment or local Sb deficiency), causing anisotropy in thermoelectric properties (such as ZT value difference >10% in different directions); too long a time will increase energy consumption, and prolonged high temperature will cause trace impurities in the melt (such as Fe and Cu remaining in the raw materials) to gradually accumulate and form impurity phases, affecting carrier mobility.

[0029] A 120-minute timeframe allows Sb or Se atoms to occupy a uniform position in the Bi-Te lattice. Stirring further eliminates microscopic concentration gradients, ensuring uniform alloy composition at the atomic level and laying the foundation for subsequent grain refinement and high performance.

[0030] Turn off the heating source and continue stirring at a speed of 20-25 rpm while simultaneously cooling to 600°C at a rate of 10°C / min. The beneficial effects of then adjusting the stirring paddle are as follows:

[0031] If the high speed of 40 r~50 r / min is maintained, it will lead to excessive load on the stirring paddle, which may damage the equipment. At the same time, the high viscosity of the melt will generate severe shear stress, which may easily form internal cracks before solidification. The low speed of 20 r~25 r / min can maintain weak convection of the melt, eliminate significant temperature and composition differences during the cooling process (such as the melt tending to accumulate on the wall surface when the crucible wall temperature is low, resulting in local component concentration), avoid component segregation, and avoid equipment overload and stress generation.

[0032] The critical range for grain growth before melt solidification is 800°C to 600°C. A cooling rate of 10°C to 15°C / min is used. If the cooling rate is too low (e.g., <10°C / min), it will give the grains ample time to grow, resulting in excessively large alloy grains (e.g., >50 μm), fewer grain boundaries, weak phonon scattering, and increased lattice thermal conductivity (the core thermoelectric performance indicator ZT value is negatively correlated with lattice thermal conductivity). If the cooling rate is too high (e.g., >15°C / min), it will cause a sharp increase in the temperature difference between the inside and outside of the crucible, leading to rapid solidification of the melt and the formation of an amorphous or metastable phase, disrupting the layered crystal structure of bismuth telluride and resulting in a significant decrease in electrical conductivity. A cooling rate of 15°C / min achieves a balance between suppressing grain growth and preserving a stable crystal structure.

[0033] At a cooling rate of 10℃~15℃ / min, the grain size can be controlled at 5~15 μm (compared to 30~80 μm for traditional methods), the number of grain boundaries increases by 3~5 times, phonon scattering is enhanced, the lattice thermal conductivity decreases by 15%~20%, and the crystal structure remains intact while the carrier mobility is unaffected.

[0034] Advantages of adjusting the stirring paddle at 600°C: 600°C is the initial solidification temperature (solid-liquid coexistence temperature) of bismuth telluride melt. Adjusting the stirring paddle at this temperature can prevent the paddle blades from sticking to the subsequently solidified alloy. If the stirring paddle is adjusted after solidification, the paddle blades are prone to causing the alloy to crack. At the same time, it prevents the paddle blades from being pressed into the alloy during solidification, thus preventing mechanical defects (such as holes and cracks) and ensuring the integrity of the material.

[0035] The beneficial effect of reducing the furnace temperature to room temperature from 600°C at a rate of 6°C / min;

[0036] The complete solidification stage of the alloy occurs from 600°C to room temperature, during which the material transitions from a liquid to a solid state with a volume shrinkage rate of approximately 3% to 5%. Continuing with a rapid cooling rate of 10°C to 15°C / min can lead to a thermal stress gradient within the material (rapid cooling and shrinkage at the surface, and slow cooling and shrinkage at the interior), easily causing macroscopic cracking (the cracking rate of traditional rapid quenching methods is >20%). A slow cooling rate of 6°C / min allows the internal and external temperatures of the material to decrease simultaneously, resulting in uniform volume shrinkage and gradual release of thermal stress. The cracking rate can be controlled to <2%, while avoiding secondary grain growth caused by excessively slow cooling (e.g., <5°C / min) (grain growth tends to continue below 600°C, and excessively slow cooling can cause the grain size to rise back to over 20 μm). This rate balances low cracking rate with fine grain size, ensuring that the alloy possesses both good mechanical strength and excellent thermoelectric properties.

[0037] S3. The product obtained in step two is uniformly refined into powder, and then loaded into a mold for compaction and sintering to obtain a high-performance bismuth telluride-based thermoelectric material.

[0038] In a preferred embodiment of this example, the purity of the Bi, Te, Sb, and Se used in S1 to prepare the N-type or P-type is above 99.99%.

[0039] High-purity raw materials can reduce the impact of impurities such as Fe and Cu on carrier mobility.

[0040] As a preferred embodiment of this example, the protective atmosphere in S2 uses N2 and Ar, both with a purity of 99.99 vol.

[0041] As a preferred embodiment of this example, the alloy homogenization and refinement in S2 is carried out by pulverization in a high-energy ball mill.

[0042] In a preferred embodiment of this example, the sintering temperature in S3 is controlled at 800°C.

[0043] In a preferred embodiment of this example, in S1, the particle size of all elemental powders is 50~200μm.

[0044] A particle size range of 50~200 μm can ensure uniform mixing and avoid the risk of oxidation caused by excessive surface area of ​​fine powder, which is compatible with the 400℃ heat preservation and dissolution step in S2.

[0045] As a preferred embodiment of this example, the fixed stirring paddle in S2 is made of quartz or silicon nitride, the blade structure is a three-bladed propeller, the blade diameter is 1 / 3 to 1 / 2 of the inner diameter of the quartz crucible, and the bottom of the blade is 5 to 8 mm away from the bottom of the crucible.

[0046] Quartz or silicon nitride materials are heat-resistant and do not react with Bi-Te melt, avoiding impeller contamination. Conventional impeller diameters are typically 1 / 4 or 2 / 3 of the crucible's inner diameter: If the diameter is too small (<1 / 3), it can only drive the melt flow in the central region, and a stagnant layer easily forms at the crucible edge, leading to component segregation (e.g., Te enrichment); if the diameter is too large (>1 / 2), the impeller blades easily rotate against the wall, causing crucible wear (quartz crucibles are brittle and prone to cracking with prolonged stirring), and the melt splashes excessively due to centrifugal force, increasing element volatilization losses. A 1 / 3 to 1 / 2 ratio can create gradient convection between the central strong turbulence zone and the edge weak circulation zone: the high-speed rotation of the central impeller blades generates strong shear force, driving the bottom melt upwards; the edge melt forms a ring circulation under the pull of the central flow, completely eliminating unstirred areas at the edges, allowing Bi, Te, and Sb / Se atoms to achieve 360° mixing without dead angles in the melt, improving component uniformity compared to conventional designs.

[0047] Bismuth telluride-based melts have low viscosity (approximately 0.05 Pa·s) at 800–900°C. Blades with a diameter of 1 / 3 to 1 / 2 can create wide-range turbulence, rapidly breaking up undissolved Te particles (Te has a melting point of 452°C and easily forms small particles in the melt). When the temperature is reduced to 600°C, the melt viscosity increases (approximately 0.2 Pa·s). Blades of this size provide moderate stirring resistance, maintaining weak convection to eliminate compositional gradients without causing blade overload or melt splashing due to excessive resistance, thus achieving stable stirring across the entire temperature range.

[0048] The close-range design of 5~8 mm can forcefully agitate the bottom melt: when Sb particles settle to the bottom, the shear flow at the bottom of the blade will directly act on the particle surface. Through the dual action of mechanical crushing and thermal convection dissolution, Sb is completely dissolved in 120 min of heat preservation and stirring (XRD shows no Sb elemental peak, proving that there are no undissolved particles), eliminating the hidden danger of component segregation from the root.

[0049] During the cooling stage (from 900°C to 600°C), the supercooling of the melt gradually increases, and the tendency to crystallize is enhanced. When the bottom of the impeller is 5-8 mm away from the bottom, the temperature of the melt at the bottom is slightly lower than that of the central region due to contact with the crucible, and it becomes the preferential nucleation zone. At this time, the stirring of the impeller can quickly disperse the fine crystal nuclei generated at the bottom into the entire melt, avoiding the accumulation and growth of crystal nuclei at the bottom. Ultimately, the grain size is refined from 30-80 μm in the traditional process to 5-15 μm, the number of grain boundaries increases by 3-5 times, significantly enhances phonon scattering, and directly improves thermoelectric performance.

[0050] In a preferred embodiment of this example, the protective gas is kept in dynamic flow at a rate of 450~600 mL / min throughout the melting process in S2.

[0051] The present invention has a reasonable structure: the bismuth telluride-based thermoelectric material prepared by this method has a more uniform alloy composition, smaller grain size, and better thermoelectric performance. Moreover, compared with the traditional zone melting method and melting-annealing method, this method is simple to operate and has a simple process, making it suitable for large-scale commercial production. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 The image shows the XRD pattern of the P-type bismuth telluride-based thermoelectric material obtained after sintering.

[0054] Figure 2 The ZT value of the obtained P-type bismuth telluride-based thermoelectric material is shown. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] Example 1

[0057] S1: According to the chemical formula (Bi) 1-y Sb y )2Te3, where 0.7≤ y ≤0.9, weigh 1 kg of high-purity powder of elemental raw materials Bi, Te and Sb according to stoichiometric ratio and put them into a quartz crucible;

[0058] S2: Place the quartz crucible containing the material into a sealed atmosphere furnace, perform a vacuum cleaning operation, and then preheat the sealed atmosphere furnace by introducing high-purity nitrogen gas at a rate of 500 ml / min. Increase the furnace temperature to 400°C at a rate of 20°C / min and hold for 30 min. At this point, slowly lower the stirrer to the melt area to begin enhanced stirring at a speed of 40 r / min. Then, continue to raise the furnace temperature to 850°C at a rate of 10°C / min. After stirring and melting for 120 min, first turn off the heating source, maintain the stirrer at 20 r / min, and then lower the furnace temperature to 600°C at a rate of 10°C / min before raising the stirrer. During this process, the melt's own convection further homogenizes the composition. Finally, slowly cool the product to room temperature at a rate of 6°C / min and remove it.

[0059] S3: After crushing, the solid product is taken out and placed in a high-energy ball mill jar for uniform refinement. Then, it is placed in a cold mold and compacted with a pressure of 8 MPa. After being placed in a tube furnace, it is sintered at a high temperature of 800°C to obtain high-performance bismuth telluride-based thermoelectric materials.

[0060] Example 2

[0061] S1: According to the chemical formula (Bi) 1-y Sb y )2Te3, where 0.7≤ y ≤0.9, weigh 1 kg of high-purity powder of elemental raw materials Bi, Te and Sb according to stoichiometric ratio and put them into a quartz crucible;

[0062] S2: Place the quartz crucible containing the material into a sealed atmosphere furnace, perform a vacuum cleaning operation, and then preheat the sealed atmosphere furnace by introducing high-purity nitrogen gas at a rate of 500 ml / min. Raise the furnace temperature to 400°C at a rate of 22°C / min and hold for 30 min. At this point, slowly lower the stirrer to the melt area to begin enhanced stirring at a speed of 45 r / min. Then, continue raising the furnace temperature to 850°C at a rate of 17°C / min and stir and melt for 120 min. First, turn off the heating source, maintain the stirrer at 23 r / min, and lower the furnace temperature to 600°C at a rate of 1°C / min. Then, raise the stirrer. During this process, utilize the melt's own convection to further homogenize the composition. Finally, slowly cool the product to room temperature at a rate of 6°C / min and remove it.

[0063] S3: After crushing, the solid product is taken out and placed in a high-energy ball mill jar for uniform refinement. Then, it is placed in a cold mold and compacted with a pressure of 8 MPa. After being placed in a tube furnace, it is sintered at a high temperature of 800°C to obtain high-performance bismuth telluride-based thermoelectric materials.

[0064] Example 3

[0065] S1: According to the chemical formula (Bi) 1-y Sb y )2Te3, where 0.7≤ y ≤0.9, weigh 1 kg of high-purity powder of elemental raw materials Bi, Te and Sb according to stoichiometric ratio and put them into a quartz crucible;

[0066] S2: Place the quartz crucible containing the material into a sealed atmosphere furnace, perform a vacuum cleaning operation, and then preheat the sealed atmosphere furnace by introducing high-purity nitrogen gas at a rate of 500 ml / min. Raise the furnace temperature to 400°C at a rate of 25°C / min and hold for 30 min. At this point, slowly lower the stirrer to the melt area to begin enhanced stirring at a speed of 50 r / min. Then, continue raising the furnace temperature to 850°C at a rate of 15°C / min and stir and melt for 120 min. First, turn off the heating source, maintain the stirrer at 25 r / min, and lower the furnace temperature to 600°C at a rate of 15°C / min. Then, raise the stirrer. During this process, utilize the melt's own convection to further homogenize the composition. Finally, slowly cool the product to room temperature at a rate of 6°C / min and remove it.

[0067] S3: After crushing, the solid product is taken out and placed in a high-energy ball mill jar for uniform refinement. Then, it is placed in a cold mold and compacted with a pressure of 8 MPa. After being placed in a tube furnace, it is sintered at a high temperature of 800°C to obtain high-performance bismuth telluride-based thermoelectric materials.

[0068] from Figure 1 It can be seen that, Figure 1 The full width at half maximum (FWHM) of the characteristic peaks (such as the main peaks near 2θ≈27°, 38°, and 45°) is significantly wider than that of the XRD peaks of bismuth telluride materials prepared by the traditional melting-annealing method (the traditional method has sharp peaks and narrow FWHM). According to the Scherrer equation... It can be seen that, under the premise of fixed λ and K, the larger β (half-width at half maximum) is, the smaller D (grain size) is, indicating that the grain size of the bismuth telluride-based thermoelectric material prepared in Example 1 is smaller. According to the Scherrer formula, the grain size is 5~15μm (far smaller than the traditional 30~80μm).

[0069] from Figure 2 It can be seen that within the range of 300~500K (room temperature to 227°C, the core application temperature range of bismuth telluride-based materials), the ZT values ​​of Examples 1 to 3 all show an increasing trend with increasing temperature, and the highest ZT value can reach 1.2~1.3 (excellent thermal properties), which is significantly higher than that of bismuth telluride materials prepared by the traditional melting-annealing method (the ZT value of the traditional method is mostly 0.8~1.0).

[0070] Furthermore, within the 300~500K range, the ZT value curves of Examples 1~3 showed no significant fluctuations (e.g., no sharp peaks / troughs). The fluctuations in ZT values ​​are essentially caused by the uneven concentration of charge carriers within the material. If there is compositional segregation (e.g., local Sb enrichment / deficiency, Te content fluctuations), it will cause differences in α and σ in different regions, which in turn causes the ZT value to fluctuate drastically with temperature. Within the 300~500K range, the ZT curves of Examples 1~3 are stable, and the performance remains consistent after small-range changes in process parameters, indicating that the internal composition of the material is highly uniform, with no local differences in charge carrier concentration; the alloy composition is even more uniform.

[0071] Depend on Figure 1 and Figure 2 It can be seen that the bismuth telluride-based thermoelectric material prepared by this method has a more uniform alloy composition, smaller grain size, and better thermoelectric performance.

[0072] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a bismuth telluride-based thermoelectric material, characterized in that, The specific steps are as follows: S1, according to the chemical formula Bi2Te of N-type bismuth telluride thermoelectric material 3-x Se x， Weigh high-purity Bi, Te, and Se elemental powders as raw materials, where 0.1 ≤ x ≤ 0.25, or according to the chemical formula of p-type bismuth telluride thermoelectric material (Bi 1-y Sb y )2Te3, where 0.7≤ y≤0.9, weigh high-purity Bi, Te and Sb elemental powders as raw materials; S2. After uniform mixing, the material is poured into a quartz crucible and placed in a sealed atmosphere furnace. A protective gas is introduced into the furnace, and a fixed stirring paddle is inserted. The atmosphere furnace is heated, with a heating rate of 20°C~25°C / min in the range of room temperature to 400°C. The temperature is then held at 400°C for 30 minutes. At this time, the stirring paddle is lowered for forced stirring at a speed of 40 r~50 r / min. Subsequently, the heating rate is 10°C~15°C / min in the range of 400°C~900°C. When the temperature reaches the set temperature of 850°C~900°C, stirring is continued for 120 minutes. The heating source is then turned off, and the stirring paddle is kept rotating at 20 r~25 r / min. The furnace temperature is lowered to 600°C at a cooling rate of 10°C~15°C / min. The stirring paddle is then raised. During this process, the composition is further homogenized by the convection of the melt itself. The product is then slowly cooled to room temperature at a rate of 6°C / min and then removed. S3. The product obtained in S2 is uniformly refined into powder, and then loaded into a mold for compaction and sintering to obtain a high-performance bismuth telluride-based thermoelectric material.

2. The method for preparing bismuth telluride-based thermoelectric materials according to claim 1, characterized in that, In S1, the purity of the Bi, Te, Sb, and Se used to prepare N-type or P-type materials is all above 99.99%.

3. The method for preparing bismuth telluride-based thermoelectric materials according to claim 1, characterized in that, The protective atmosphere in S2 consists of N2 and Ar, both with a purity of 99.99 vol.

4. The method for preparing bismuth telluride-based thermoelectric materials according to claim 1, characterized in that, In S2, the alloy is uniformly refined by pulverizing in a high-energy ball mill.

5. The method for preparing bismuth telluride-based thermoelectric materials according to claim 1, characterized in that, The sintering temperature in S3 is controlled at 800°C.

6. The method for preparing bismuth telluride-based thermoelectric materials according to claim 1, characterized in that, In S1, the particle size of all elemental powders is 50~200 μm.

7. The method for preparing bismuth telluride-based thermoelectric materials according to claim 1, characterized in that, The fixed stirring paddle described in S2 is made of quartz or silicon nitride, and the blade structure is a three-bladed propeller. The diameter of the blade is 1 / 3 to 1 / 2 of the inner diameter of the quartz crucible, and the bottom of the blade is 5 to 8 mm away from the bottom of the crucible.

8. The method for preparing bismuth telluride-based thermoelectric materials according to claim 1, characterized in that, Throughout the smelting process in S2, the protective gas is kept in a dynamic flow at a rate of 450~600 mL / min.

Images