An n-type bismuth telluride-based thermoelectric material and a method for preparing the same

Abstract

The application relates to a high-performance n-type bismuth telluride-based thermoelectric material and a preparation method thereof, and belongs to the technical field of thermoelectric conversion. The chemical composition of the n-type bismuth telluride-based thermoelectric material is La y Bi 2‑ y Te 2.7 Se 0.3 -xwt%Te, 0<=x<=1.5, 0<=y<=0.015, x and y are not 0 at the same time. Under the premise of fixing the Se doping amount, the application reduces the Te element to increase Te vacancies, reduces the carrier concentration, moves the dimensionless thermoelectric optimization value zT peak to the low-temperature direction, simultaneously utilizes La-doped Bi to optimize the electrothermal transport performance, and finally realizes the obvious improvement of the zT value.

Description

Technical Field

[0001] This invention relates to a high-performance n-type bismuth telluride-based thermoelectric material and its preparation method, belonging to the field of thermoelectric conversion technology. Background Technology

[0002] Thermoelectric cooling technology is currently a relatively mature solid-state cooling technology. Thermoelectric cooling devices (TECs) have become indispensable core temperature control components in many application scenarios due to their advantages such as small size, no noise, high reliability, customizability, precise temperature control, and environmental friendliness, including 5G optical communication modules and PCR testing instruments. The maximum cooling temperature difference achievable by thermoelectric cooling devices... ΔT max This reflects the temperature control capability of thermoelectric devices, which mainly depends on the dimensionless thermoelectric figure of merit of the thermoelectric material. zT = S 2 σT / κ tot ,in S It is the Seebeck coefficient of the material. σ It is electrical conductivity. κ tot It is the total thermal conductivity. T This refers to absolute temperature. Therefore, the main method to improve the cooling performance of thermoelectric refrigeration devices (TECs) is to enhance the dimensionless thermoelectric figure of merit of the thermoelectric material at its service temperature. zT Currently, thermoelectric materials can be realized through optimizing carrier concentration, band engineering, and nanotechnology. zT Significant improvement.

[0003] Bismuth telluride-based thermoelectric materials are typical narrow bandgap semiconductors, and their complex multi-valley band structure is also conducive to improving their thermoelectric performance. Researchers have improved the thermoelectric properties of these materials by optimizing their electrical transport properties or enhancing phonon scattering to reduce thermal conductivity through methods such as elemental doping, bandgap modification, texturing, and nanocrystalline or nano-second-phase composites. However, optimizing the performance of bismuth telluride-based thermoelectric materials below 400 K still faces challenges. Summary of the Invention

[0004] To address the issue of low near-room-temperature thermoelectric performance of existing n-type bismuth telluride (BiTeSe) materials, this invention provides an n-type bismuth telluride-based thermoelectric material and its preparation method. By reducing the Te element to increase Te vacancies while keeping the Se doping level constant, the carrier concentration is lowered, resulting in a dimensionless thermoelectric figure of merit. zT The peak value shifts towards lower temperatures, while La-doped Bi is used to optimize electrothermal transport properties, ultimately achieving... zT The value has increased significantly.

[0005] In a first aspect, the present invention provides an n-type bismuth telluride-based thermoelectric material. The chemical composition of the n-type bismuth telluride-based thermoelectric material is La. y Bi 2-y Te 2.7 Se 0.3 - x wt% Te, 0 ≤ x ≤ 1.5, 0 ≤ y ≤ 0.015, x , y Not both are 0. This invention is based on La. y Bi 2-y Te 2.7 Se 0.3 The Te content is reduced from the total Te mass. Therefore, "-" refers to a minus sign. x This refers to the percentage of Te content that is reduced compared to La content. y Bi 2-y Te 2.7 Se 0.3 The percentage of the total mass of Te. y It refers to the unit (one) La y Bi 2-y Te 2.7 Se 0.3 The number of La (doped) atoms in the molecule.

[0006] Preferably, 1.0 ≤ x ≤ 1.4.

[0007] Preferably, 0 ≤ y ≤ 0.01.

[0008] Preferably, the n-type bismuth telluride-based thermoelectric material has a Seebeck coefficient of -120 to -280 μV / K at 300 to 500 K and an electrical conductivity of 0.9 × 10⁻⁶. 4 ~7.5×10 4 S / m, thermal conductivity of 0.8~2.2 W / m K at 300~500K, and thermoelectric figure of merit at 300~400K. zT The value is 0.85~0.95.

[0009] Secondly, the present invention provides a method for preparing an n-type bismuth telluride-based thermoelectric material. The preparation method includes: weighing elemental La, elemental Bi, elemental Te, and elemental Se according to the stoichiometric ratio of the n-type bismuth telluride-based thermoelectric material, and mixing them to obtain a mixture; sintering the mixture to obtain the n-type bismuth telluride-based thermoelectric material.

[0010] Preferably, the sintering is spark plasma sintering, the sintering atmosphere is a vacuum atmosphere, the sintering temperature is 350~450℃, and the sintering time is 3~10 minutes.

[0011] Preferably, the method further includes: ball milling the mixture under a protective atmosphere before sintering.

[0012] Preferably, the protective atmosphere is an inert atmosphere.

[0013] Preferably, the ball milling speed is 600~1200 rpm and the ball milling time is 6~48 hours.

[0014] Secondly, this invention provides a method for improving the room temperature (≤ 400K) thermoelectric performance of bismuth telluride-based thermoelectric materials. The chemical formula of the bismuth telluride material is La. y Bi 2-y Te 2.7 Se 0.3 - x wt% Te, 0 ≤ x ≤ 1.5, 0 ≤ y ≤0.015, x , y They are not both 0. Attached Figure Description

[0015] Figure 1 Bi2Te 2.7 Se 0.3 - x wt%Te ( x X-ray diffraction pattern of (=0,0.5,1,1.25,1.5);

[0016] Figure 2 For La y Bi 2-y Te 2.7 Se 0.3 -1.25wt%Te ( y X-ray diffraction patterns of (=0,0.005,0.01,0.015);

[0017] Figure 3 Bi2Te 2.7 Se 0.3 - x wt% Te ( x Conductivity plot of (=0,0.5,1,1.25,1.5);

[0018] Figure 4 For La y Bi 2-y Te 2.7 Se 0.3 -1.25wt% Te ( y Conductivity plots for (=0, 0.005, 0.01, 0.015);

[0019] Figure 5 Bi2Te 2.7 Se 0.3 - x wt% Te ( x Seebeck coefficient plot for (=0,0.5,1,1.25,1.5);

[0020] Figure 6 For La y Bi 2-y Te 2.7 Se 0.3 -1.25wt%Te ( y Seebeck coefficient plot for (=0,0.005,0.01,0.015);

[0021] Figure 7 Bi2Te 2.7 Se 0.3 - x wt% Te ( x Thermal conductivity plot of (=0,0.5,1,1.25,1.5);

[0022] Figure 8 For La y Bi 2-y Te 2.7 Se 0.3 -1.25wt%Te ( y Thermal conductivity plots for values ​​of 0, 0.005, 0.01, and 0.015.

[0023] Figure 9 Bi2Te 2.7 Se 0.3 - x wt%Te ( x =0,0.5,1,1.25,1.5) zT value;

[0024] Figure 10 For La y Bi 2-y Te 2.7 Se 0.3 -1.25wt%Te ( y =0,0.005,0.01,0.015) zT value. Detailed Implementation

[0025] The present invention is further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0026] The chemical formula of the n-type bismuth telluride-based thermoelectric material of this invention is La. yBi 2-y Te 2.7 Se 0.3 - x wt%Te, 0 ≤ x ≤ 1.5, 0 ≤ y ≤ 0.015, x , y The values ​​are not both zero. This invention, through special material design, reduces the Te element to increase Te vacancies, thereby lowering the carrier concentration and achieving a dimensionless thermoelectric figure of merit. zT The peak value shifts towards lower temperatures, while La-doped Bi is used to optimize electrical transport properties, ultimately achieving... zT The value has increased significantly.

[0027] In other words, this invention also proposes a method to improve the room temperature (≤ 400K) thermoelectric performance of bismuth telluride-based thermoelectric materials by reducing the Te content and doping with La, wherein the chemical formula of the bismuth telluride material is La. y Bi 2-y Te 2.7 Se 0.3 - x wt%Te, 0 ≤ x ≤ 1.5, 0 ≤ y ≤ 0.015, x , y They are not both 0.

[0028] This invention is based on La y Bi 2-y Te 2.7 Se 0.3 The Te content is reduced from the total Te mass. Therefore, "-" refers to a minus sign. x This refers to the percentage of Te content that is reduced compared to La content. y Bi 2-y Te 2.7 Se 0.3 The percentage of the total mass of Te. y It refers to the unit (one) La y Bi 2-y Te 2.7 Se 0.3 The number of La (doped) atoms in the molecule. Reducing the Te content decreases the occupancy of Te atoms, resulting in a cation-to-anion ratio greater than 2:3 in this invention.

[0029] Existing Bi2Te 3-x Se x Thermoelectric materials utilize Se to replace Te atoms while maintaining a fixed molar ratio of Bi atoms to the total amount of Te and Se atoms at 2:3. Existing Bi₂Te… 2.7-x Se0.3-y The thermoelectric material reduces the proportion of Te or Se atoms, decreasing the number of anions and thus increasing the molar ratio of cations to anions, making the cation-to-anion ratio of the bismuth telluride compound greater than 2:3. The La of this invention... y Bi 2-y Te 2.7 Se 0.3 - x By fixing the amount of Se anions and reducing the amount of Te anions, and by substituting some Bi atoms with La atoms, the simultaneous regulation of cations and anions is achieved. The main reason for fixing Se and altering Te in this invention is that, compared to Se atoms, Te atoms have a larger atomic radius and mass. Reducing the number of Te atoms is more conducive to increasing the mass fluctuations and stress fluctuations within the material, enhancing phonon scattering, and reducing lattice thermal conductivity. Furthermore, while regulating only anions increases anion vacancies and reduces the material's current carrier concentration, shifting the peak zT towards lower temperatures, it also leads to bipolar diffusion at even lower temperatures, increasing the material's thermal conductivity and thus deteriorating its low-temperature thermoelectric performance. Therefore, regulating only anions without regulating cations cannot solve the problem of low near-room-temperature thermoelectric performance in n-type bismuth telluride materials.

[0030] Preferably, 1.0 ≤ x ≤ 1.4. x Within this range, the electrical properties of the material are basically the same as those of the matrix, while the thermal conductivity near room temperature decreases.

[0031] As a preferred option, 0≤ y ≤0.01. y Within this range, the electrical properties of the material are improved while the near-room temperature thermal conductivity does not deteriorate significantly.

[0032] Existing Bi2Te 2.7-x Se 0.3-y The thermoelectric material reduces the Te / Se ratio, making the cation-to-anion ratio of the bismuth telluride compound greater than 2:3, thus reducing the number of anions and introducing anion vacancies. These anion vacancies effectively compensate for the deficiencies of the donor-like effect, inducing the generation of sufficient electrons and enhancing the carrier concentration. Simultaneously, the increased distribution of vacancy defects improves the phonon scattering probability, which is beneficial for reducing lattice thermal conductivity. Furthermore, the large number of introduced anion vacancies are uniformly dispersed within the grains, thereby strengthening the mechanical strength of the n-type bismuth telluride bulk material. However, the La of this invention... y Bi 2-y Te 2.7 Se 0.3 - x wt%Te based on the defect equation of n-type bismuth telluride materials Reducing the Te element and increasing Te vacancies can effectively lower the carrier concentration inside the matrix, thereby increasing the peak value of bismuth telluride materials. zT Moving towards lower temperatures improves the low-temperature thermoelectric properties of materials.

[0033] Bi2Te 2.7-x Se 0.3-y Thermoelectric materials and the La of the present invention y Bi 2-y Te 2.7 Se 0.3 Although both -xwt%Te and other methods reduce the number of Te anions and introduce anion vacancies, the carrier concentrations show completely opposite trends. The main reason for this phenomenon is likely the difference in material preparation processes. CN114538927A's Bi2Te... 2.7-x Se 0.3-y The sample was first prepared using rocking melt synthesis, followed by ball milling and sintering. During ball milling, the bismuth telluride grains prepared by rocking melt were repeatedly compressed and deformed, leading to changes in the intrinsic defects within the material. The defect equation is as follows: This will generate more electrons and increase the carrier concentration.

[0034] The La of the present invention will be described by way of example below. y Bi 2-y Te 2.7 Se 0.3 - x Preparation method of wt%Te thermoelectric material.

[0035] Weigh the elements La, Bi, Te, and Se according to their stoichiometric ratio and mix them thoroughly to obtain a mixture. When weighing, first weigh according to the ratio of La... y Bi 2-y Te 2.7 Se 0.3 Calculate the required masses of La, Bi, Te, and Se, and then reduce the mass of Te by a percentage of its mass. The elemental La, Bi, Te, and Se can be in powder or bulk form, with no size limitation.

[0036] The resulting mixture is ball-milled under a protective atmosphere, such as nitrogen. The ball-to-material ratio refers to the mass ratio of grinding balls to material. The ball milling speed can be 600–1200 rpm, and the milling time can be 6–48 hours. Ball milling can yield micro / nano-scale powders, which is beneficial for obtaining bismuth telluride-based thermoelectric materials with low thermal conductivity. For example, the size of the ball-milled mixture is 0.5–20 μm.

[0037] The ball-milled mixture is then sintered. Preferably, the sintering is spark plasma sintering. For example, the sintering atmosphere is a vacuum atmosphere, the sintering temperature is 350~450℃, and the sintering time is 3~10 minutes.

[0038] The Seebeck coefficient of the n-type bismuth telluride-based thermoelectric material is -120 to -280 μV / K at 300 to 500 K.

[0039] The conductivity of the n-type bismuth telluride-based thermoelectric material is 0.9 × 10⁻⁶. 4 ~7.5×10 4 S / m.

[0040] The n-type bismuth telluride-based thermoelectric material has a thermal conductivity of 0.8 to 2.2 W / m K at 300 to 500 K.

[0041] The n-type bismuth telluride-based thermoelectric material exhibits excellent thermoelectric performance at 300-400K. zT The value is 0.85~0.95. For example, the n-type bismuth telluride-based thermoelectric material has an average value of 0.85~0.95 at 300K~400K. zT The value is approximately 0.87.

[0042] In summary, this invention, while maintaining a fixed Se doping level, reduces the Te element to increase Te vacancies, thereby lowering the carrier concentration and resulting in a dimensionless thermoelectric figure of merit. zT The peak value shifts towards lower temperatures, while La-doped Bi is used to optimize electrothermal transport properties, ultimately achieving material... zT A significant increase in value. For example, the n-type bismuth telluride-based thermoelectric material of the present invention. zT The peak temperature can be reduced to 300K, which significantly improves the near-room temperature thermoelectric performance of bismuth telluride-based thermoelectric materials.

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should also be understood that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0044] Example 1

[0045] (1) According to the chemical formula La y Bi 2-y Te 2.7 Se 0.3 - x wt%Te ( x =0.5, yWeigh out elemental Bi, elemental Te, and elemental Se powders in the ratio of 0 and mix them. Then, load the mixture into a ball mill jar filled with argon gas and mechanically ball mill for 8 hours at a ball-to-powder ratio of 6:1 and a rotation speed of 1200 rpm to obtain alloy powder.

[0046] (2) The alloy powder was placed in a glove box into a graphite mold with a diameter of 10 mm, and then placed in a spark plasma sintering furnace for sintering. Vacuum treatment was carried out until the vacuum degree was 10 Pa. The sintering furnace was heated to the sintering temperature of 400 °C and the pressure was gradually increased to 50 MPa. After reaching the sintering temperature and pressure, the temperature and pressure were held for 5 min. Then the sample was cooled to room temperature with the furnace body to obtain a cylinder of n-type bismuth telluride-based thermoelectric material with a height of 9~11 mm.

[0047] Example 2

[0048] (1) According to the chemical formula La y Bi 2-y Te 2.7 Se 0.3 - x wt%Te ( x =1, y Weigh out elemental La, Bi, Te, and Se powders in the ratio of 0 and mix them. Place the mixture into a ball mill jar filled with argon gas and mechanically ball mill for 8 hours at a ball-to-powder ratio of 6:1 and a rotation speed of 1200 rpm to obtain alloy powder.

[0049] (2) The alloy powder was placed in a glove box into a graphite mold with a diameter of 10 mm, and then placed in a spark plasma sintering furnace for sintering. Vacuum treatment was carried out until the vacuum degree was 10 Pa. The sintering furnace was heated to the sintering temperature of 400 °C and the pressure was gradually increased to 50 MPa. After reaching the sintering temperature and pressure, the temperature and pressure were held for 5 min. Then the sample was cooled to room temperature with the furnace body to obtain a cylinder of n-type bismuth telluride-based thermoelectric material with a height of 9~11 mm.

[0050] Example 3

[0051] (1) According to the chemical formula La y Bi 2-y Te 2.7 Se 0.3 - x wt%Te ( x =1.25, y Weigh out elemental La, Bi, Te, and Se powders in the ratio of 0 and mix them. Place the mixture into a ball mill jar filled with argon gas and mechanically ball mill for 8 hours at a ball-to-powder ratio of 6:1 and a rotation speed of 1200 rpm to obtain alloy powder.

[0052] (2) The alloy powder was placed in a glove box into a graphite mold with a diameter of 10 mm, and then placed in a spark plasma sintering furnace for sintering. Vacuum treatment was carried out until the vacuum degree was 10 Pa. The sintering furnace was heated to the sintering temperature of 400 °C and the pressure was gradually increased to 50 MPa. After reaching the sintering temperature and pressure, the temperature and pressure were held for 5 min. Then the sample was cooled to room temperature with the furnace body to obtain a cylinder of n-type bismuth telluride-based thermoelectric material with a height of 9~11 mm.

[0053] Example 4

[0054] (1) According to the chemical formula La y Bi 2-y Te 2.7 Se 0.3 - x wt% Te ( x =1.5, y Weigh out elemental La, Bi, Te, and Se powders in the ratio of 0 and mix them. Place the mixture into a ball mill jar filled with argon gas and mechanically ball mill for 8 hours at a ball-to-powder ratio of 6:1 and a rotation speed of 1200 rpm to obtain alloy powder.

[0055] (2) The alloy powder was placed in a glove box into a graphite mold with a diameter of 10 mm, and then placed in a spark plasma sintering furnace for sintering. Vacuum treatment was carried out until the vacuum degree was 10 Pa. The sintering furnace was heated to the sintering temperature of 400 °C and the pressure was gradually increased to 50 MPa. After reaching the sintering temperature and pressure, the temperature and pressure were held for 5 min. Then the sample was cooled to room temperature with the furnace body to obtain a cylinder of n-type bismuth telluride-based thermoelectric material with a height of 9~11 mm.

[0056] Example 5

[0057] (1) According to the chemical formula La y Bi 2-y Te 2.7 Se 0.3 - x wt%Te ( x =1.25, y Weigh out elemental La, Bi, Te, and Se powders in a ratio of 0.005 and mix them. Then, load the mixture into a ball mill jar filled with argon and mechanically ball mill for 8 hours at a ball-to-powder ratio of 6:1 and a rotation speed of 1200 rpm to obtain alloy powder.

[0058] (2) The alloy powder was placed in a glove box into a graphite mold with a diameter of 10 mm, and then placed in a spark plasma sintering furnace for sintering. Vacuum treatment was carried out until the vacuum degree was 10 Pa. The sintering furnace was heated to the sintering temperature of 400 °C and the pressure was gradually increased to 50 MPa. After reaching the sintering temperature and pressure, the temperature and pressure were held for 5 min. Then the sample was cooled to room temperature with the furnace body to obtain a cylinder of n-type bismuth telluride-based thermoelectric material with a height of 9~11 mm.

[0059] Example 6

[0060] (1) According to the chemical formula La y Bi 2-y Te 2.7 Se 0.3 - x wt%Te ( x =1.25, y Weigh out elemental La, Bi, Te, and Se powders in a ratio of 0.01 and mix them. Then, load the mixture into a ball mill jar filled with argon and mechanically ball mill for 8 hours at a ball-to-powder ratio of 6:1 and a rotation speed of 1200 rpm to obtain alloy powder.

[0061] (2) The alloy powder was placed in a glove box into a graphite mold with a diameter of 10 mm, and then placed in a spark plasma sintering furnace for sintering. Vacuum treatment was carried out until the vacuum degree was 10 Pa. The sintering furnace was heated to the sintering temperature of 400 °C and the pressure was gradually increased to 50 MPa. After reaching the sintering temperature and pressure, the temperature and pressure were held for 5 min. Then the sample was cooled to room temperature with the furnace body to obtain a cylinder of n-type bismuth telluride-based thermoelectric material with a height of 9~11 mm.

[0062] Example 7

[0063] (1) According to the chemical formula La y Bi 2-y Te 2.7 Se 0.3 - x wt%Te ( x =1.25, y Weigh out elemental La, Bi, Te, and Se powders in a ratio of 0.015 and mix them. Then, load the mixture into a ball mill jar filled with argon and mechanically ball mill for 8 hours at a ball-to-powder ratio of 6:1 and a rotation speed of 1200 rpm to obtain alloy powder.

[0064] (2) The alloy powder was placed in a glove box into a graphite mold with a diameter of 10 mm, and then placed in a spark plasma sintering furnace for sintering. Vacuum treatment was carried out until the vacuum degree was 10 Pa. The sintering furnace was heated to the sintering temperature of 400 °C and the pressure was gradually increased to 50 MPa. After reaching the sintering temperature and pressure, the temperature and pressure were held for 5 min. Then the sample was cooled to room temperature with the furnace body to obtain a cylinder of n-type bismuth telluride-based thermoelectric material with a height of 9~11 mm.

[0065] Comparative Example 1

[0066] (1) According to the chemical formula La y Bi 2-y Te 2.7 Se 0.3 - x wt%Te ( x =0, y Weigh out elemental Bi, elemental Te, and elemental Se powders in the ratio of 0 and mix them. Then, load the mixture into a ball mill jar filled with argon gas and mechanically ball mill for 8 hours at a ball-to-powder ratio of 6:1 and a rotation speed of 1200 rpm to obtain alloy powder.

[0067] (2) The alloy powder was placed in a glove box into a graphite mold with a diameter of 10 mm, and then placed in a spark plasma sintering furnace for sintering. Vacuum treatment was carried out until the vacuum degree was 10 Pa. The sintering furnace was heated to the sintering temperature of 400 °C and the pressure was gradually increased to 50 MPa. After reaching the sintering temperature and pressure, the temperature and pressure were held for 5 min. Then the sample was cooled to room temperature with the furnace body to obtain a cylinder of n-type bismuth telluride-based thermoelectric material with a height of 9~11 mm.

[0068] Figure 1 It is an n-type bismuth telluride thermoelectric material Bi2Te 2.7 Se 0.3 - x The X-ray diffraction (XRD) pattern of wt%Te, where the vertical axis represents the intensity of the diffraction peaks and the horizontal axis represents the angle of the diffraction peaks. From Figure 1 As can be seen from the data, reducing the Te content did not result in the appearance of a second phase in the diffraction peaks, indicating that the structure of the material was not changed as a result.

[0069] Figure 2 For La y Bi 2-y Te 2.7 Se 0.3 X-ray diffraction (XRD) pattern of -1.25wt%Te. Figure 2 It can be seen that no obvious second-phase diffraction peaks were observed in the XRD of the La-doped sample, indicating that La was incorporated into the bismuth telluride lattice.

[0070] The Seebeck coefficient and conductivity of bismuth telluride-based thermoelectric materials were measured using the commercial Seebeck coefficient / resistance measurement system ZEM (ULVAC-RIKO, ZEM-3). Thermal conductivity of the samples was measured using a laser thermal conductivity meter (Netzsch, LFA 457). The results were obtained according to the dimensionless thermoelectric figure of merit formula. zT = S 2 σT / κ tot , S The Seebeck coefficient, σ For electrical conductivity, T Absolute temperature κ tot The total thermal conductivity is used to calculate the sample's... zT value.

[0071] Figure 3 Bi2Te 2.7 Se 0.3 - x Conductivity of wt% Te in the range of 300–500 K. For Bi₂Te 2.7 Se 0.3 - x wt%Te sample, with x The increase in Te content leads to a decrease in Te vacancies, which in turn causes a decrease in carrier concentration, resulting in a decrease in the sample's conductivity. x The increase leads to a decrease.

[0072] Figure 4 For La y Bi 2-y Te 2.7 Se 0.3 Conductivity diagram of -1.25wt% Te at 300~500K. La y Bi 2-y Te 2.7 Se 0.3 The -1.25wt%Te sample generally exhibits a change in conductivity with increasing La doping concentration. y The increasing trend is due to the increase in carrier concentration caused by La doping.

[0073] Figure 5 Bi2Te 2.7 Se 0.3 - x Seebeck coefficient plot for wt% Te at 300–500 K. For Bi₂Te 2.7 Se 0.3 - x wt%Te sample, with xWith the increase of (i.e., the decrease of Te content), the material as a whole shows a trend of increasing absolute value of the Seebeck coefficient near room temperature (300~350K, especially 300K). This is mainly due to the fact that... x The increase in Te content leads to a decrease in Te vacancies, which in turn causes a decrease in the carrier concentration of the material.

[0074] Figure 6 For La y Bi 2-y Te 2.7 Se 0.3 Seebeck coefficient plot for -1.25wt%Te at 300~500K. For La y Bi 2- y Te 2.7 Se 0.3 -1.25wt%Te sample, with La doping amount y With the increase of La doping, the material as a whole shows a trend of decreasing absolute value of Seebeck coefficient near room temperature (300~400K), which is due to the increase of carrier concentration inside the sample caused by La doping.

[0075] Figure 7 Bi2Te 2.7 Se 0.3 - x Thermal conductivity of wt% Te at 300–500 K. For Bi₂Te 2.7 Se 0.3 - x wt%Te sample, with x With the increase of Te content, the material as a whole exhibits a trend of first decreasing and then increasing thermal conductivity near room temperature (300K). On the one hand, with... x The increase in Te content, i.e., the decrease in Te content, introduces a large number of Te vacancies, which can effectively reduce the lattice thermal conductivity of the material; on the other hand, with the... x The increase in Te content leads to a decrease in the internal carrier concentration of the material, which in turn reduces the electronic thermal conductivity. However, as the internal carrier concentration decreases, the bipolar diffusion temperature of the material also decreases to near room temperature, resulting in an increase in the thermal conductivity of the sample.

[0076] Figure 8 For La y Bi 2-y Te 2.7 Se 0.3 Thermal conductivity diagram of -1.25wt% Te at 300~500K. For La y Bi 2- y Te 2.7 Se 0.3For the -1.25wt%Te sample, with increasing La doping content... y With the increase of La doping, the overall thermal conductivity of the sample gradually increases near room temperature (300K). This is mainly because La doping increases the carrier concentration of the material, thereby increasing the carrier thermal conductivity.

[0077] Figure 9 Bi2Te 2.7 Se 0.3 - x wt% Te in 300~500K zT Value. For Bi2Te 2.7 Se 0.3 - x wt% Te sample, with x The increase in Te content, i.e., the decrease in Te content, results in the material reaching its peak at 300K. zT It continues to move towards the low temperature zone, and the overall temperature is close to room temperature. zT along with x The increase showed a trend of first increasing and then decreasing. Additionally, from... Figure 9 It can be seen that when x At a value of 1.5, the peak value is 300K. zT Approximately 0.22 ， This indicates that the thermoelectric properties of the sample have deteriorated.

[0078] Figure 10 For La y Bi 2-y Te 2.7 Se 0.3 -1.25wt%Te at 300~500K zT Value. For La y Bi 2-y Te 2.7 Se 0.3 -1.25wt%Te sample, with La doping amount y With the increase of [something], the sample as a whole exhibited near-room temperature (300K). zT A trend of first increasing and then decreasing. Specifically, when... y When the value is 0.005, the material at 300K zT The value is approximately 0.85. Additionally, from... Figure 10 It can be seen that when y When =0.015, at 300K zT Approximately 0.63 ， This indicates that the thermoelectric properties of the sample have deteriorated.

[0079] In summary, this invention, while maintaining a fixed Se doping level, successfully reduced the Te content and utilized La doping to achieve the desired effect. zTThe peak temperature was reduced from 400K to 300K, which improved the near-room temperature thermoelectric performance of bismuth telluride-based thermoelectric materials.

Claims

1. An n-type bismuth telluride-based thermoelectric material, characterized in that, The chemical composition of the n-type bismuth telluride-based thermoelectric material is La. y Bi 2-y Te 2.7 Se 0.3 - x wt% Te, x This refers to the percentage of Te content that is reduced compared to La content. y Bi 2-y Te 2.7 Se 0.3 The percentage of total mass of Te in the total mass. y This refers to the unit La. y Bi 2-y Te 2.7 Se 0.3 The number of La-doped atoms in the Te molecule, 1.0 ≤ x ≤ 1.4, 0.005 < y ≤ 0.01; The preparation method of the n-type bismuth telluride-based thermoelectric material includes: weighing elemental La, elemental Bi, elemental Te, and elemental Se according to the stoichiometric ratio of the n-type bismuth telluride-based thermoelectric material, and mixing them to obtain a mixture; ball milling the mixture under a protective atmosphere to obtain alloy powder; and sintering the alloy powder to obtain the n-type bismuth telluride-based thermoelectric material.

2. The n-type bismuth telluride-based thermoelectric material according to claim 1, characterized in that, The n-type bismuth telluride-based thermoelectric material has a Seebeck coefficient of -120 to -280 μV / K at 300–500 K and an electrical conductivity of 0.9 × 10⁻⁶. 4 ~7.5×10 4 S / m, thermal conductivity of 0.8~2.2 W / m K at 300~500K, and thermoelectric figure of merit at 300~400K. zT The value is 0.85~0.

95.

3. The n-type bismuth telluride-based thermoelectric material according to claim 1, characterized in that, The sintering is spark plasma sintering, the sintering atmosphere is a vacuum atmosphere, the sintering temperature is 350~450℃, and the sintering time is 3~10 minutes.

4. The n-type bismuth telluride-based thermoelectric material according to claim 1, characterized in that, The protective atmosphere is an inert atmosphere.

5. The n-type bismuth telluride-based thermoelectric material according to claim 1, characterized in that, The ball milling speed is 600~1200 rpm, and the ball milling time is 6~48 hours.

6. A method for improving the near-room-temperature thermoelectric performance of n-type bismuth telluride-based thermoelectric materials, characterized in that, The chemical formula of the n-type bismuth telluride thermoelectric material is La. y Bi 2-y Te 2.7 Se 0.3 - x wt% Te, x This refers to the percentage of Te content that is reduced compared to La content. y Bi 2- y Te 2.7 Se 0.3 The percentage of total mass of Te in the total mass. y This refers to the unit La. y Bi 2-y Te 2.7 Se 0.3 The number of La-doped atoms in the Te molecule, 1.0 ≤ x ≤ 1.4, 0.005 < y ≤ 0.01; The preparation method of the n-type bismuth telluride-based thermoelectric material includes: weighing elemental La, elemental Bi, elemental Te, and elemental Se according to the stoichiometric ratio of the n-type bismuth telluride-based thermoelectric material, and mixing them to obtain a mixture; ball milling the mixture under a protective atmosphere to obtain alloy powder; and sintering the alloy powder to obtain the n-type bismuth telluride-based thermoelectric material.

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