A method for preparing N-type bismuth telluride based on fusion bonding plastic deformation

Abstract

The application discloses a method for preparing N-type bismuth telluride based on plastic deformation of melting combination, and belongs to the technical field of thermoelectric material preparation. The method comprises the following steps: weighing raw materials of N-type bismuth telluride powder, vacuum packaging, heating and melting, and cooling to obtain a ingot with uniform composition; grinding the obtained ingot into fine powder by using an agate mortar; then performing first spark plasma sintering on the powder to obtain a densified block; finally, performing second spark plasma sintering on the block, and applying pressure to induce plastic deformation in the sintering process; and through the adjustment of deformation temperature, pressure and strain rate, the grain preferred orientation and micro defect are cooperatively optimized. The application adopts a step-by-step spark plasma sintering plastic deformation process, significantly improves the thermoelectric performance of bismuth telluride material, especially the power factor and ZT value, and has the advantages of simple process, short cycle, good repeatability, suitable for industrial production and the like.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric material preparation technology, and particularly relates to a method for preparing an N-type bismuth telluride thermoelectric material. Background Technology

[0002] Thermoelectric conversion technology, as a green energy technology, enables the direct conversion between heat and electricity, effectively recovering waste heat without generating any pollution. Bismuth telluride-based thermoelectric materials are among the best-performing thermoelectric materials near room temperature and are widely used in thermoelectric refrigeration and waste heat recovery. Their thermoelectric performance is typically characterized by the dimensionless thermoelectric figure of merit ZT = (S²σ / κ)T, where S is the Seebeck coefficient, σ is the electrical conductivity, and κ is the thermal conductivity. To improve the ZT value, it is necessary to synergistically optimize both electrical and thermal transport properties.

[0003] Currently, common methods for preparing bismuth telluride-based thermoelectric materials include zone melting, hot pressing, hot extrusion, and spark plasma sintering (SPS). Crystals prepared by zone melting exhibit a distinct preferred orientation and high thermoelectric performance, but the material's mechanical properties are poor, and it is prone to cleavage and cracking. Hot pressing and conventional SPS methods can obtain dense, fine-grained bulk materials, improving mechanical properties, but it is usually difficult to simultaneously achieve ideal grain orientation, resulting in a low power factor. Traditional hot deformation processes often require independent equipment and multiple steps, making the process complex, time-consuming, and prone to microcracks or component segregation during deformation. In recent years, some studies have attempted to combine spark plasma sintering with hot deformation, i.e., performing a second SPS hot deformation after a first SPS densification. However, existing methods often directly use commercially available or zone-melted ingot crushed powder as raw material, resulting in uneven powder particle size, compositional deviations from stoichiometry, and a lack of systematic optimization of the second deformation process parameters (temperature, pressure, strain rate, etc.), leading to limited performance improvements.

[0004] Therefore, developing a simple, uniform preparation method that can effectively improve the thermoelectric properties of bismuth telluride materials, especially for the n-type BiTeSe system, has important practical application value. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for preparing N-type bismuth telluride based on melt-bonded plastic deformation. This method is simple to operate, has high repeatability, and can produce large quantities of relatively pure samples. The N-type bismuth telluride thermoelectric material prepared by the plastic deformation sintering method of this invention has high thermoelectric figure of merit and good application prospects.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention proposes a method for preparing N-type bismuth telluride based on melt-bonded plastic deformation, characterized by comprising the following steps:

[0008] (1) Weigh the Bi powder, Te powder, and Se powder in a vacuum glove box;

[0009] (2) Vacuum seal the weighed powder;

[0010] (3) The sealed raw material is placed in a muffle furnace and heated to melt, to obtain an alloyed ingot;

[0011] (4) The obtained alloyed ingot is crushed and ground to obtain powder;

[0012] (5) The powder is loaded into a mold and pressed into a block by spark plasma sintering;

[0013] (6) After removing the carbon paper covering the block, the block is subjected to discharge plasma sintering under programmed automatic sintering control to obtain the N-type bismuth telluride material.

[0014] In the plastic deformation preparation method of the N-type bismuth telluride thermoelectric material of this invention, vacuum sealing can isolate air, avoid the oxidation of raw materials to form impurity phases, and reduce interference with electrical transport properties. Melting and casting ensures uniform composition; the first discharge plasma sintering can rapidly achieve powder densification and inhibit excessive grain growth; the second discharge plasma sintering allows the bulk material to undergo plastic deformation under axial pressure. Due to the increased mold diameter (from 12.7 mm to 15 mm), the material is forced to flow radially outward, inducing a preferential orientation of grains perpendicular to the pressure direction, significantly improving carrier mobility and conductivity, while also greatly enhancing the power factor. The preparation process only requires a conventional muffle furnace and the same SPS equipment, with clearly defined and controllable parameters, simple operation, and good industrial repeatability.

[0015] Further, in step (1), the molar ratio of Bi powder, Te powder and Se powder is 2:2.7:0.3.

[0016] Further, in step (2), the vacuum sealing is achieved by drawing the quartz tube containing the raw material powder into a vacuum using a vacuum pump and then sealing it with an oxyhydrogen flame.

[0017] Further, in step (3), the heating and melting process involves loading a vacuum-sealed quartz tube into a muffle furnace and heating it from room temperature to 1073K over 300 minutes, holding it at 1073K for 600 minutes, and then cooling it with the furnace after the holding period.

[0018] Furthermore, in step (4), the alloyed ingot obtained by heating and melting is crushed and ground into fine powder using an agate mortar at a pressure of 20 MPa for 5 min.

[0019] Further, in step (5), the powder is loaded into a 12.7 mm diameter mold and pre-pressed at 10 MPa. The discharge plasma sintering includes the following steps: setting the pressure to 50 MPa, the program has a 30 s preparation time, heating to 673 K for 10 min, holding at 673 K for 20 min, then depressurizing and cooling to room temperature in a vacuum environment.

[0020] Further, in step (6), the removal of the carbon paper coating is achieved by sanding the carbon paper coating on the surface of the block obtained by the first discharge plasma sintering.

[0021] Furthermore, in step (6), the block is placed into a mold with a diameter of 15mm, and the programmed automatic sintering control is a computer program that controls the sintering process according to the preset sintering parameters.

[0022] Further, in step (6), the programmed automatic sintering temperature control program is as follows: the program has a 30s preparation time, the room temperature is raised to 773K after 10min, and the temperature is held at 773K for 20min. The programmed automatic sintering pressure control program is as follows: the pressure is raised to 1KN in 30s, held at 1KN for 10min, raised to 8.8KN in 10min, held at 8.8KN for 10min, and then the pressure is released and cooled to room temperature in a vacuum environment.

[0023] The present invention also provides an N-type bismuth telluride thermoelectric material, which is prepared according to the preparation method described above.

[0024] Compared with the prior art, the present invention has the following advantages and technical effects:

[0025] (1) This invention provides a method for preparing N-type bismuth telluride based on melt-bonded plastic deformation. This method is simple and produces samples with stable performance. Through a multi-step synergistic process of “melting and casting → fine grinding in an agate mortar → rapid densification by first Φ12.7mm mold discharge plasma sintering → automatic hot deformation by second Φ15mm mold discharge plasma sintering,” preferential grain orientation is achieved to improve carrier mobility and conductivity. At the same time, plastic deformation increases the Seebeck coefficient through energy filtering effect, resulting in a significant improvement in the power factor. The room temperature ZT value of the n-type bismuth telluride thermoelectric material increases from 0.39 to 0.65, which is about 66.7% higher than that of the undeformed sample; and at a temperature of 423K, the ZT value increases from 0.52 to 0.80, which is about 53.8% higher than that of the undeformed sample.

[0026] (2) In this invention, after plastic deformation by two discharge plasma sintering, the electrical conductivity and Seebeck coefficient increase synchronously and the power factor is significantly enhanced; at the same time, κL+κb remains stable, avoiding the rebound of lattice thermal conductivity, thereby overcoming the shortcomings of traditional hot deformation in which the increase of κe leads to the limitation of ZT improvement.

[0027] (3) The present invention only requires a conventional muffle furnace and a spark plasma sintering device. The two SPS are completed on the same device by changing the mold and calling the programmed automatic sintering program, without the need for additional hot pressing, hot forging or extrusion equipment.

[0028] (4) The method of the present invention is simple to operate, short in time and highly repeatable. Attached Figure Description

[0029] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0030] Figure 1 The image shows the XRD pattern of the N-type bismuth telluride thermoelectric material obtained in Example 1.

[0031] Figure 2 The image shows a SEM image of the N-type bismuth telluride thermoelectric material obtained in Example 1.

[0032] Figure 3 The thermal properties of the N-type bismuth telluride thermoelectric materials obtained before and after plastic deformation in Examples 1-2 and Comparative Examples 1-2 are shown in the diagram.

[0033] Figure 4 The electrical properties and ZT value test results of the N-type bismuth telluride thermoelectric materials obtained before and after plastic deformation in Examples 1-2 and Comparative Examples 1-2 are shown.

[0034] Figure 5 The thermal properties of N-type bismuth telluride thermoelectric materials obtained at different plastic deformation temperatures in Examples 1-2 and Comparative Examples 1-2 are shown in the diagram.

[0035] Figure 6 The electrical properties and ZT value test results of the N-type bismuth telluride thermoelectric materials obtained at different plastic deformation temperatures in Examples 1-2 and Comparative Examples 1-2 are shown. Detailed Implementation

[0036] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0037] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0038] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0039] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0040] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0041] This invention provides a method for preparing N-type bismuth telluride based on melt-bonded plastic deformation, comprising the following steps:

[0042] (1) Weigh Bi powder, Te powder, and Se powder in a vacuum glove box;

[0043] (2) Vacuum seal the weighed powder;

[0044] (3) The sealed raw material is placed in a muffle furnace and heated to melt, to obtain an alloyed ingot;

[0045] (4) The obtained alloyed ingot is crushed and ground to obtain powder;

[0046] (5) The powder is loaded into a mold and pressed into a block by spark plasma sintering;

[0047] (6) After removing the carbon paper covering the block, the block is subjected to discharge plasma sintering under programmed automatic sintering control to obtain the N-type bismuth telluride material.

[0048] In step (1) of the preferred embodiment of the present invention, the molar ratio of Bi powder, Te powder and Se powder is 2:2.7:0.3.

[0049] In step (2) of the preferred embodiment of the present invention, vacuum sealing is performed by drawing the quartz tube containing the raw material powder into a vacuum using a vacuum pump and then sealing it by molten hydrogen-oxygen flame.

[0050] In step (3) of the preferred embodiment of the present invention, the heating and melting process is to load the vacuum-sealed quartz tube into the muffle furnace and heat it from room temperature to 1073K in 300 minutes, hold it at 1073K for 600 minutes, and then cool it with the furnace after the holding period.

[0051] In step (4) of the preferred embodiment of the present invention, the alloyed ingot is heated and melted, and then crushed and ground into fine powder using an agate mortar and pestle at a pressure of 20 MPa for 5 min.

[0052] In step (5) of the preferred embodiment of the present invention, the powder is loaded into a mold with a diameter of 12.7 mm and pre-pressed at 10 MPa. The discharge plasma sintering includes the following steps: setting the pressure to 50 MPa, having a 30-second preparation time in the program, heating to 673 K for 10 minutes, holding at 673 K for 20 minutes, then depressurizing and cooling to room temperature in a vacuum environment.

[0053] In step (6) of the preferred embodiment of the present invention, the carbon paper covering is removed by sanding the carbon paper covering the surface of the block obtained by the first discharge plasma sintering.

[0054] In step (6) of the preferred embodiment of the present invention, the block is loaded into a mold with a diameter of 15mm, and the programmed automatic sintering control is the sintering process controlled by a computer program according to the preset sintering parameters.

[0055] In step (6) of the preferred embodiment of the present invention, the programmed automatic sintering temperature control program is as follows: the program has a 30s preparation time, the room temperature is raised to 773K after 10min, and the temperature is held at 773K for 20min. The programmed automatic sintering pressure control program is as follows: the pressure is raised to 1KN in 30s, held at 1KN for 10min, raised to 8.8KN in 10min, held at 8.8KN for 10min, and then the pressure is released and cooled to room temperature in a vacuum environment.

[0056] In this invention, during the heating and melting process, a vacuum-sealed quartz tube is slowly heated from room temperature to 1073 K over 300 minutes, held at that temperature for 600 minutes, and then cooled with the furnace. The prolonged slow heating and sufficient holding effectively prevent the volatilization loss of high vapor pressure elements (Te, Se), and the vacuum environment eliminates oxidation, resulting in an alloyed ingot with accurate composition and uniform microstructure. Subsequently, the ingot is crushed and ground in an agate mortar under 20 MPa pressure for 5 minutes to obtain fine powder with a uniform particle size distribution, ensuring sintering activity while avoiding excessive introduction of impurities.

[0057] During spark plasma sintering (SPS), the powder is first loaded into a 12.7 mm diameter mold and pre-compressed at 10 MPa. Then, an axial pressure of 50 MPa is applied, and the temperature is raised to 673 K after 10 min (this temperature is much lower than the melting temperature of BiTeSe material, 1073 K), and held for 20 min. The Joule heat generated by the pulsed current during SPS is highly concentrated at the contact points of the powder particles, which can achieve rapid densification at 673 K and effectively suppress excessive grain growth. After holding, the pressure is released and cooled to room temperature in a vacuum environment, which can release the sintering internal stress, reduce residual porosity (porosity causes fluctuations in thermal conductivity), and make the crystal structure more regular.

[0058] In this invention, during the second spark plasma sintering (plastic deformation) process, the high-density bulk material obtained from the first sintering is placed into a 15 mm diameter mold. Programmed automatic sintering control is employed, meaning the sintering and deformation processes are automatically completed by a computer program according to pre-set sintering parameters. During this process, the Joule heating generated by the pulsed current rapidly brings the sample to the plastic deformation temperature (773 K, far below the melting temperature). Simultaneously, stepped pressure loading (first 1 KN pre-compression for 10 min, then slowly increasing to 8.8 KN) avoids microcracks or sample cracking caused by sudden large deformations, allowing the material to undergo uniform plastic deformation in radial flow and inducing preferential grain orientation perpendicular to the pressure direction. After holding at this temperature, the pressure is released and vacuum cooling is performed, effectively preserving the deformed microstructure and dislocation structure. Programmed automatic control ensures high consistency of temperature, pressure, and time parameters in each experiment, significantly improving the repeatability of the process.

[0059] The bulk material prepared according to the above steps is a high-density bulk material with a relative density ρ / ρ0 ≥ 94%, where ρ is the measured density of the sample and ρ0 is the theoretical density of the material. This high density ensures a continuous transport path for charge carriers, resulting in high electrical conductivity, while simultaneously reducing the scattering fluctuations of thermal conductivity caused by pores, thus making the thermoelectric properties more stable.

[0060] This invention also provides an N-type bismuth telluride thermoelectric material, prepared according to a specific method.

[0061] In the embodiment of this invention, the BiTeSe phase is dominant in the fusion-bonded step-discharge plasma sintering plastic deformation thermoelectric material, and there are no obvious impurity phases in the sample. The electrical performance parameters are significantly improved after plastic deformation, with a power factor (PF) of ~2.17mWm-1K-2 and a thermoelectric figure of merit (ZT) of ~0.8.

[0062] The Bi powder, Te powder, and Se powder used in the embodiments of the present invention have a particle size of less than 200 mesh and a purity of ≥99.999%.

[0063] In this invention, room temperature refers to "25±2℃".

[0064] In this invention, the thermal conductivity of the material is calculated using the formula k=DdCp. Here, D represents the thermal diffusivity of the sample, d represents the density of the sample, and Cp represents the specific heat of the sample. The density of the material is measured by the water displacement method; the thermal diffusivity is measured using a laser thermal conductivity meter LFA467 (temperature range: -100~500℃) and LFA467 HT (temperature range: room temperature~1200℃) manufactured by Netzsch GmbH, Germany. The thermal diffusivity is directly measured using the laser scattering method. After the laser emits a laser beam, an infrared detector can detect the change in temperature rise signal at the other end of the sample over time. Under heat-insulated conditions, the thermal diffusivity D of the sample can be calculated using the formula... The calculation yields a value where l is the thickness of the sample being tested, and t1 / 2 is the time required for the back of the sample to reach a temperature rise of 1 / 2.

[0065] The electrical performance testing method in this invention was performed using a CTA-3 (room temperature - 1000℃) instrument manufactured by Beijing Kerui Co., Ltd. The instrument's working principle is as follows: When the furnace temperature rises to the set temperature, the temperature difference heater in the bottom support rod begins to heat to the set temperature, creating a temperature difference. Temperature and voltage are measured using two thermocouple probes, with temperatures T1 and T2 obtained from the upper and lower probes, and voltages U1 and U2, respectively. The Seebeck coefficient can then be calculated using the formula... Calculations show that the upper and lower electrodes and the upper and lower probes together form a four-probe method for resistivity testing. Therefore, the conductivity of the sample can be expressed by the formula... Obtained through calculation.

[0066] The technical solution of the present invention will be further illustrated by the following embodiments.

[0067] Example 1

[0068] (1) Weigh Bi powder, Te powder and Se powder in a molar ratio of 2:2.7:0.3 and put them into a quartz tube;

[0069] (2) The quartz tube is evacuated to a vacuum and then melted and sealed with an oxyhydrogen flame to obtain a vacuum-sealed quartz tube containing the raw material;

[0070] (3) The vacuum-sealed quartz tube is placed in a muffle furnace and heated to above the melting point for melting treatment, and then cooled and solidified to obtain an alloy ingot with uniform composition;

[0071] (4) Take out the quartz tube containing the sample after alloying pretreatment, and take out the sample. Grind it in an agate mortar at a pressure of 20 MPa for 5 min to obtain uniform powder.

[0072] (5) After the uniform powder is placed into the graphite mold, it is pre-pressed by a pressure of 10MPa and pressed into a block by spark plasma sintering. Specifically, the pressure is adjusted to 50MPa, the room temperature is raised to 673K ​​after 10 minutes, the temperature is held at 673K ​​for 20 minutes, and then cooled to room temperature in a vacuum environment.

[0073] (6) The programmed automatic sintering of the block includes the following steps: plastic deformation program (using a mold with a diameter of 15 mm, the sample diameter after sintering is 15 mm, pressure setting (8.8 KN = 50 MPa). The programmed automatic sintering of the block is performed with the following automatic pressure: 30 s to 1 KN, 1 KN held for 10 min, 10 min to 8.8 KN, 8.8 KN held for 10 min, temperature setting: the program has a 30 s preparation time, room temperature is raised to 773 K after 10 min, 773 K is held for 20 min, then the pressure is released and cooled to room temperature in a vacuum environment to obtain N-type bismuth telluride thermoelectric material.

[0074] Example 2

[0075] Same as Example 1, except that in step (6), the block is programmed to automatically sinter the temperature: the program has a 30s preparation time, the room temperature is raised to 673K ​​after 10min, the temperature is held at 673K ​​for 20min, and then the pressure is released and cooled to room temperature in a vacuum environment to obtain N-type bismuth telluride thermoelectric material.

[0076] Example 3

[0077] Same as Example 1, except that in step (6), the block is programmed to automatically sinter the temperature: the program has a 30s preparation time, the room temperature is raised to 723K after 10min, the temperature is held at 723K for 20min, and then the pressure is released and cooled to room temperature in a vacuum environment to obtain N-type bismuth telluride thermoelectric material.

[0078] Comparative Example 1

[0079] Same as Example 1, except that step (6) of automatically sintering the block is omitted. Specifically:

[0080] (1) Weigh Bi powder, Te powder and Se powder in a molar ratio of 2:2.7:0.3 and put them into a quartz tube;

[0081] (2) The quartz tube is evacuated to a vacuum and then melted and sealed with an oxyhydrogen flame to obtain a vacuum-sealed quartz tube containing the raw material;

[0082] (3) The vacuum-sealed quartz tube is placed in a muffle furnace and heated to above the melting point for melting treatment, and then cooled and solidified to obtain an alloy ingot with uniform composition;

[0083] (4) Take out the quartz tube containing the sample after alloying pretreatment, and take out the sample. Grind it in an agate mortar at a pressure of 20 MPa for 5 min to obtain uniform powder.

[0084] (5) After the uniform powder is placed into the graphite mold, it is pre-pressed by a pressure of 10 MPa and pressed into a block by spark plasma sintering. Specifically, the pressure is adjusted to 50 MPa, the temperature is raised to 673 K after 10 min at room temperature, and held at 673 K for 20 min. Then it is cooled to room temperature in a vacuum environment, and then the pressure is released and cooled to room temperature in a vacuum environment to obtain N-type bismuth telluride thermoelectric material. Performance testing

[0085] The XRD pattern of the product obtained in Example 1 is shown in Figure 1. Figure 1 It can be seen that the diffraction peaks of the synthesized N-type bismuth telluride thermoelectric material are basically consistent with the diffraction peaks of the BiTeSe standard card, indicating that the BiTeSe phase with a specific crystal structure was successfully synthesized, and no obvious impurity peaks appeared.

[0086] SEM images of the product obtained in Example 1 are shown below. Figure 2 It can be seen that the synthesized N-type bismuth telluride thermoelectric material exhibits a distinct layered structure.

[0087] Example 1 differs from Comparative Example 1 only in that step (6) of automatically sintering the block is omitted. Its main thermal properties are shown in the figure. Figure 3 As shown in the figure, (a) represents the total thermal conductivity, (b) represents the electronic thermal conductivity, (c) represents the lattice thermal conductivity, and (d) represents the thermal diffusivity. It can be seen from the figure that after plastic deformation, the total thermal conductivity of the material increases, the electronic thermal conductivity increases significantly, while the lattice thermal conductivity (κL) and bipolar diffusion thermal conductivity (κb) do not change much.

[0088] Example 1 differs from Comparative Example 1 only in that step (6) of automatically sintering the block is omitted. Its main electrical properties are shown in the figure below. Figure 4As shown in the figure, (a) represents electrical conductivity, (b) represents the power factor, (c) represents the Seebeck coefficient, and (d) represents the ZT value. It can be seen from the figure that after plastic deformation, the electrical conductivity, Seebeck coefficient, and power factor (PF) of the material all increase significantly. For anisotropic bismuth telluride, the crystal orientation increases after deformation (usually the c-axis is perpendicular to the pressure direction). Along the in-plane direction (the measurement direction), carrier mobility increases significantly (because layered materials have good in-plane conductivity), which leads to a simultaneous increase in electrical conductivity σ and Seebeck coefficient S (through changes in effective carrier mass or energy filtering effects), thus increasing PF. However, the significant increase in mobility also means that the contribution of carriers to thermal transport (electronic thermal conductivity κe = L·σ·T, following the Wiedmann-Franz law) will increase, because κe is positively correlated with electrical conductivity σ. Therefore... Figure 3 The increase in κe is natural and inevitable. Ultimately, this increases the room temperature ZT value of the n-type bismuth telluride thermoelectric material from 0.39 to 0.65, an increase of approximately 66.7% compared to the undeformed sample; and at a temperature of 423 K, the ZT value increases from 0.52 to 0.80, an increase of approximately 53.8% compared to the undeformed sample.

[0089] The thermal properties of N-type bismuth telluride thermoelectric materials obtained at different plastic deformation temperatures in Examples 1-3 are shown in the figure. Figure 5 Where (a) is the total thermal conductivity, (b) is the electronic thermal conductivity, (c) is the lattice thermal conductivity, and (d) is the thermal diffusivity. The material was plastically deformed at temperatures of 673 K, 723 K, and 773 K. As can be seen from the figure, with the increase of the plastic deformation temperature, the total thermal conductivity, electronic thermal conductivity, lattice thermal conductivity (κL), and bipolar diffusion thermal conductivity (κb) of the sample first increase and then decrease.

[0090] The electrical properties and ZT value test results of the N-type bismuth telluride thermoelectric materials obtained at different plastic deformation temperatures in Examples 1-3 are shown in the figure. Figure 6 Where (a) is electrical conductivity, (b) is power factor, (c) is Seebeck coefficient, and (d) is ZT value. The material was plastically deformed at temperatures of 673 K, 723 K, and 773 K. As can be seen from the figure, the electrical conductivity of the sample did not fluctuate significantly with increasing plastic deformation temperature, but the Seebeck coefficient increased significantly at the plastic deformation temperature of 773 K, and the power factor was also significantly optimized at 773 K. Finally, the ZT value reached 0.65 at room temperature, and at a temperature of 423 K, the ZT value increased from 0.52 to 0.80.

[0091] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing N-type bismuth telluride based on melt-bonded plastic deformation, characterized in that, Includes the following steps: (1) Weigh Bi powder, Te powder, and Se powder in a vacuum glove box; (2) Vacuum seal the weighed powder; (3) The sealed raw material is placed in a muffle furnace and heated to melt, to obtain an alloyed ingot; (4) The obtained alloyed ingot is crushed and ground to obtain powder; (5) The powder is loaded into a mold and pressed into a block by spark plasma sintering; (6) After removing the carbon paper covering the block, the block is subjected to discharge plasma sintering under programmed automatic sintering control to obtain the N-type bismuth telluride material.

2. The method for preparing N-type bismuth telluride according to claim 1, characterized in that, In step (1), the molar ratio of Bi powder, Te powder and Se powder is 2:2.7:0.

3.

3. The method for preparing N-type bismuth telluride according to claim 1, characterized in that, In step (2), the vacuum sealing is achieved by pumping the quartz tube containing the raw material powder into a vacuum using a vacuum pump and then sealing it with an oxyhydrogen flame.

4. The method for preparing N-type bismuth telluride according to claim 1, characterized in that, In step (3), the heating and melting process involves loading a vacuum-sealed quartz tube into a muffle furnace and heating it from room temperature to 1073K over 300 minutes, holding it at 1073K for 600 minutes, and then cooling it with the furnace after the holding period.

5. The method for preparing N-type bismuth telluride according to claim 1, characterized in that, In step (4), the alloyed ingot obtained by heating and melting is crushed and ground into fine powder using an agate mortar and pestle at a pressure of 20 MPa for 5 min.

6. The method for preparing N-type bismuth telluride according to claim 1, characterized in that, In step (5), the powder is loaded into a 12.7 mm diameter mold and pre-pressed at 10 MPa. The discharge plasma sintering includes the following steps: setting the pressure to 50 MPa, the program has a 30 s preparation time, heating to 673 K for 10 min, holding at 673 K for 20 min, then depressurizing and cooling to room temperature in a vacuum environment.

7. The method for preparing N-type bismuth telluride according to claim 1, characterized in that, In step (6), the removal of the carbon paper coating involves sanding the carbon paper coating on the surface of the block obtained by the first discharge plasma sintering.

8. The method for preparing N-type bismuth telluride according to claim 1, characterized in that, In step (6), the block is loaded into a mold with a diameter of 15mm. The programmed automatic sintering control is a computer program that controls the sintering process according to the preset sintering parameters.

9. The method for preparing N-type bismuth telluride according to claim 1, characterized in that, In step (6), the programmed automatic sintering temperature control program is as follows: the program has a 30s preparation time, the room temperature is raised to 773K after 10min, and the temperature is held at 773K for 20min. The programmed automatic sintering pressure control program is as follows: the pressure is raised to 1KN in 30s, held at 1KN for 10min, raised to 8.8KN in 10min, held at 8.8KN for 10min, and then the pressure is released and cooled to room temperature in a vacuum environment.

10. An N-type bismuth telluride thermoelectric material, characterized in that, It is prepared according to any one of claims 1-9.

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