A thermoelectric material and a method of making the same

Abstract

This application provides a thermoelectric material and its preparation method. The thermoelectric material uses SnTe as a matrix, with MnSb₂Te₄ dissolved in it, and is doped with Eu and Bi. The thermoelectric material retains the single-phase SnTe. Lattice defects are introduced into SnTe through MnSb₂Te₄ dissolution and Eu and Bi doping. These lattice defects include Mn and Sb impurity atoms and vacancies introduced through MnSb₂Te₄ dissolution, and Eu and Bi impurity atoms introduced through Eu and Bi doping. In this preparation method, vacancy engineering is introduced through alloying the ternary MnSb₂Te₄ compound with SnTe, thereby optimizing the thermoelectric transport properties of SnTe. Then, the carrier concentration is optimized through two-step Eu and Bi doping, resulting in a significant improvement in the thermoelectric performance of the obtained SnTe-based thermoelectric material across the entire test temperature range.

Description

Technical Field

[0001] This application relates to the field of energy materials technology, and in particular to a thermoelectric material and its preparation method. Background Technology

[0002] Thermoelectric materials are "green" materials that can directly convert heat energy and electrical energy into each other, and have great application potential in fields such as waste heat power generation. However, to achieve efficient conversion, the material needs to possess two seemingly contradictory properties: "high electrical transport properties" and "low thermal transport properties".

[0003] Currently, lead telluride (PbTe) performs well in the medium temperature range (approximately 500-900K, commonly found in industrial and automotive waste heat), but its toxic lead content limits its applications. Therefore, attention has turned to tin telluride (SnTe), which has a similar structure to PbTe but is non-toxic. However, SnTe has two main drawbacks: 1. Its intrinsic carrier concentration is too high, and its band structure is not ideal, resulting in a low Seebeck coefficient and low thermoelectric conversion efficiency; 2. Its thermal conductivity is also relatively high (high lattice thermal conductivity), making it easy for heat to escape and hindering the maintenance of temperature differences.

[0004] Therefore, how to obtain thermoelectric materials with excellent thermoelectric properties and non-toxicity is an urgent problem to be solved. Summary of the Invention

[0005] This application provides a thermoelectric material and its preparation method. The thermoelectric performance of the thermoelectric material is significantly improved across the entire test temperature range. At the same time, the preparation method of the thermoelectric material of this invention also has the advantages of simple process, easy large-scale production and strong practicality.

[0006] In a first aspect, a thermoelectric material is provided, characterized in that the thermoelectric material is based on SnTe, with MnSb2Te4 dissolved in solid solution, and doped with Eu and Bi; the thermoelectric material retains the single-phase SnTe; wherein, by dissolving MnSb2Te4 in solid solution and doping with Eu and Bi, lattice defects are introduced into SnTe; the lattice defects include: two impurity atoms, Mn and Sb, and vacancies introduced by dissolving MnSb2Te4 in solid solution; and two impurity atoms, Eu and Bi, introduced by doping with Eu and Bi.

[0007] In conjunction with the first aspect, in one implementation of the first aspect, the chemical composition of the thermoelectric material is Sn. 1-y- z Eu y Bi zTe + x%MnSb2Te4, where 0 < x ≤ 12, 0 < y ≤ 0.01, 0 < z ≤ 0.025; x is preferably 10 - 12, more preferably 10; y is preferably 0.005 - 0.01, more preferably 0.005; z is preferably 0.015 - 0.025, more preferably 0.015.

[0008] Combined with the first aspect, in a certain implementation manner of the first aspect, the electrical conductivity of the thermoelectric material is much lower than that of SnTe; wherein, the lattice defects introduced by solid - solution of MnSb2Te4 reduce the carrier mobility, thereby reducing the electrical conductivity; the lattice defects introduced by doping Eu and Bi reduce the carrier concentration, thereby reducing the electrical conductivity.

[0009] Combined with the first aspect, in a certain implementation manner of the first aspect, the Seebeck coefficient of the thermoelectric material is much higher than that of SnTe; wherein, the lattice defects introduced by solid - solution of MnSb2Te4 change the electron transport characteristics, thereby enhancing the Seebeck coefficient of the thermoelectric material; the lattice defects introduced by doping Eu and Bi reduce the carrier concentration, and the Seebeck coefficient is inversely proportional to the carrier concentration of the material, thereby enhancing the Seebeck coefficient of the thermoelectric material.

[0010] Combined with the first aspect, in a certain implementation manner of the first aspect, the total thermal conductivity of the thermoelectric material is much lower than that of SnTe; wherein, the total thermal conductivity includes the electronic thermal conductivity and the lattice thermal conductivity; the lattice defects introduced by solid - solution of MnSb2Te4 reduce the electrical conductivity of the thermoelectric material, thereby reducing the electronic thermal conductivity of the thermoelectric material; the lattice defects inhibit phonon transmission, reducing the lattice thermal conductivity of the thermoelectric material.

[0011] Combined with the first aspect, in a certain implementation manner of the first aspect, the figure of merit of the thermoelectric material is much higher than that of SnTe; wherein, the lattice defects introduced by solid - solution of MnSb2Te4 and doping Eu and Bi enhance the Seebeck coefficient and reduce the total thermal conductivity, thereby enhancing the figure of merit.

[0012] In the second aspect, a preparation method of the thermoelectric material according to the first aspect is provided, including the following steps: S1. Mix the elemental substances Sn, Te, Mn, Sb, Eu, and Bi according to the stoichiometric ratio of the chemical formula Sn 1-y-z Eu y Bi z Te + x%MnSb2Te4; S2. Vacuum - melt and anneal the mixed material to obtain a composition of Sn 1-y-z Eu y Bi zS3, Grinding the ingot into powder; wherein, the ingot is ground using an agate mortar and sieved through a 160-200 mesh stainless steel sieve to obtain powder; S4, The powder is subjected to discharge plasma sintering to obtain thermoelectric material.

[0013] In conjunction with the second aspect, in one implementation of the second aspect, in step S2, the vacuum melting temperature is 900~1000℃ and the vacuum melting time is 10~20h; the annealing temperature is 600℃ and the annealing time is 48h~72h.

[0014] In conjunction with the second aspect, in one implementation of the second aspect, in step S2, during the vacuum melting process, the ambient temperature of the material to be melted and mixed is adjusted to an intermediate temperature at a first speed and held for 1 to 2 hours; the intermediate temperature is adjusted to the vacuum melting temperature at a second speed, and the vacuum melting temperature is 900 to 1000°C; wherein the first speed is greater than the second speed, the intermediate temperature is a preset temperature, or the intermediate temperature is 2 / 5 to 1 / 2 times the vacuum melting temperature.

[0015] In conjunction with the second aspect, in one implementation of the second aspect, in step S4, the discharge plasma sintering is carried out under conditions of a temperature of 550~580 ℃, a pressure of 40~60 MPa, and a hot-pressing time of 5~10 min; wherein, S4, discharging the powder into a thermoelectric material by discharge plasma sintering, includes: after discharging the powder into a discharge plasma sintering, lowering the temperature of the current environment to an intermediate temperature and the pressure to an intermediate pressure, and holding the temperature and pressure for 1~5 min; lowering the temperature of the current environment to room temperature and depressurizing to remove the thermoelectric material from the current environment; wherein, the intermediate temperature is a preset temperature, or the intermediate temperature is 0.35~0.75 times the plasma sintering temperature; the intermediate pressure is a preset pressure, or the intermediate pressure is 0.35~0.75 times the plasma sintering pressure. Attached Figure Description

[0016] Figure 1A The powder X-ray diffraction patterns of various embodiments provided in this application are shown.

[0017] Figure 1B It shows Figure 1A Enlarged view of the strongest diffraction peak of the (200) crystal plane.

[0018] Figure 2A The diagram illustrates the variation of sample conductivity σ(a) with temperature in various embodiments provided in this application.

[0019] Figure 2BThe diagram illustrates the variation of the Seebeck coefficient S(b) with temperature in various embodiments provided in this application.

[0020] Figure 3 The total thermal conductivity κ of the samples provided in the embodiments of this application is shown. tot A diagram illustrating the change with temperature.

[0021] Figure 4 The diagram illustrates the variation of the thermoelectric figure of merit ZT of the samples in various embodiments provided in this application with temperature.

[0022] Figure 5A The room temperature carrier concentrations for four typical samples are shown.

[0023] Figure 5B The room temperature quality factor B of four typical samples is shown as a comparison.

[0024] Figure 6 The average ZT (ZT) of four typical samples in the temperature range of 300-823 K is shown. ave )contrast. Detailed Implementation

[0025] The embodiments of this application are described in detail below, with examples of these embodiments shown in the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0026] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0027] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are open-ended expressions, meaning they include what is specified in this application but do not exclude other aspects.

[0028] In the description of this application, all figures disclosed herein, whether or not the words "approximately" or "about" are used, are approximate values. Each figure may vary by less than 10% or by a difference that is considered reasonable by one of the art, such as 1%, 2%, 3%, 4%, or 5%.

[0029] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "a-b'" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0030] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions.

[0031] Thermoelectric materials are a type of green, novel functional material that enables the direct conversion between thermal and electrical energy. Thermoelectric devices based on thermoelectric materials have advantages such as simple structure, long service life, no noise, and no wear. They have been widely used in deep-sea and deep-space probe power supplies and refrigeration, and show great promise in the field of waste heat power generation.

[0032] The performance of thermoelectric materials is usually measured by the dimensionless thermoelectric figure of merit ZT, which is generally expressed as ZT = S. 2 σT / κ. Where S is the Seebeck coefficient, σ is the conductivity, and S 2 σ is called the power factor PF, which represents the electrical transport capacity of a material; κ is the total thermal conductivity, including electronic thermal conductivity κ. e and lattice thermal conductivity κ lat, which represents the material's thermal transport capacity; T is the Kelvin temperature. As can be seen from the expression, at a given temperature, the stronger the material's electrical transport capacity and the weaker its thermal transport capacity, the greater its thermoelectric figure of merit ZT.

[0033] Waste heat from industry and automobiles typically occurs in the 500-900K temperature range, representing a significant potential for waste heat power generation. PbTe and its alloys (ZT > 2.0) exhibit excellent performance in this temperature range, but their application is limited due to the toxicity of Pb. Consequently, SnTe, with a similar lattice and band structure to PbTe, has attracted increasing attention. High-performance thermoelectric materials require both high electrical transport properties and low thermal transport properties. However, due to SnTe's excessively high intrinsic carrier concentration and less-than-ideal intrinsic band structure, coupled with its relatively high lattice thermal conductivity, the thermoelectric performance of SnTe-based materials is significantly lower than that of PbTe.

[0034] One possible improvement method, such as doping with "Sb2Te3", can reduce thermal conductivity by creating "vacancies" in the crystal structure, but it will also significantly increase the carrier concentration of the material. At the same time, if other elements are used to adjust the "electrical conductivity" in the future, improper selection of elements will damage the "potential" of the material's thermoelectric properties (i.e., the quality factor B).

[0035] In view of this, this application provides a SnTe-based thermoelectric material that can significantly reduce the thermal conductivity of SnTe material, precisely optimize its carrier concentration to a better level, and maintain its thermoelectric performance potential. Therefore, this application prepares a high-performance, non-toxic SnTe-based thermoelectric material suitable for medium and low temperature waste heat power generation. The composition and preparation method of this material are described below by way of example.

[0036] One embodiment of this application provides a thermoelectric material with a chemical composition of Sn. 1-y-z Eu y Bi z Te + x%MnSb2Te4, where 0 <x≤12,0<y≤0.01,0<z≤0.025。

[0037] For example, x can take values ​​of 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12; y can take values ​​of 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01; z can take values ​​of 0.001, 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009, 0.01, 0.011, 0.012, 0.013, 0.014, 0.015, 0.016, 0.017, 0.018, 0.019, 0.020, 0.021, 0.022, 0.023, 0.024, 0.025.

[0038] In one possible implementation, x is in the range of 10 to 12, more preferably 10; y is in the range of 0.005 to 0.01, more preferably 0.005; and z is in the range of 0.015 to 0.025, more preferably 0.015.

[0039] Understandably, after determining that the SnTe solid solution contained Mn, Sb and Te components, the inventors conducted numerous experiments to determine that using MnSb2Te4 could enable the prepared thermoelectric material to achieve excellent performance (details will be described below).

[0040] This application also provides a method for preparing the thermoelectric material, specifically including the following steps:

[0041] S1, according to the chemical formula Sn 1-y-z Eu y Bi z The stoichiometric ratio of Te + x%MnSb2Te4 is achieved by mixing the elements Sn, Te, Mn, Sb, Eu, and Bi.

[0042] For example, according to stoichiometry Sn 1-y-z Eu y Bi z The ingredients can be prepared as follows: Te + x%MnSb2Te4. For example, Sn can be used as an ingredient. 1-y-z Eu y Bi zWeigh Sn grains, Te grains, Mn flakes, Sb grains, Eu grains, and Bi grains according to the stoichiometric ratio of Te + x%MnSb2Te4. Optionally, the purity of Sn grains, Te grains, Mn flakes, Sb grains, Eu grains, and Bi grains is greater than 99%. This can ensure the controllability and predictability of material properties, reduce impurity interference, improve the repeatability of the synthesis process, and enhance the quality and reliability of the final product. Mix the elemental raw materials Sn, Te, Mn, Sb, Eu, and Bi, and vacuum-seal the mixed material in a quartz tube.

[0043] In a possible implementation, weigh each material according to the range requirements of 0 < x ≤ 12, 0 < y ≤ 0.01, 0 < z ≤ 0.025. Among them, the specific values of x, y, and z can be selected according to the experimental principles. To determine the preferred values of x, y, and z, 7 embodiments designed in this application are given below.

[0044] Example 1: x = 8, y = 0, z = 0. That is, the material chemical formula is SnTe + 8%MnSb2Te4.

[0045] Example 2: x = 10, y = 0, z = 0. That is, the material chemical formula is SnTe + 10%MnSb2Te4.

[0046] Example 3: x = 12, y = 0, z = 0. That is, the material chemical formula is SnTe + 12%MnSb2Te4.

[0047] Example 4: x = 10, y = 0.005, z = 0. That is, the material chemical formula is Sn 0.995 Eu 0.005 Te + 10%MnSb2Te4.

[0048] Example 5: x = 10, y = 0.01, z = 0. That is, the material chemical formula is Sn 0.99 Eu 0.01 Te + 10%MnSb2Te4.

[0049] Example 6: x = 10, y = 0.005, z = 0.015. That is, the material chemical formula is Sn 0.98 Eu 0.005 Bi 0.015 Te +​​​​​​​​​​​It should be understood that the number of embodiments designed in the actual experiment is much greater. To improve readability, only a few representative embodiments that reflect the material properties are given here.

[0052] S2. The mixed material is vacuum melted and annealed to obtain a composition of Sn. 1-y-z Eu y Bi z Ingots of Te + x%MnSb2Te4.

[0053] For example, after weighing the individual elemental materials obtained in step S1, the quartz tube containing these mixed materials is vacuum-sealed and then placed in a muffle furnace for melting. For example, the vacuum melting temperature is 900~1000℃, for example, 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, 960℃, 970℃, 980℃, 990℃, or 1000℃. For example, the vacuum melting time is 10~20 hours, for example, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 hours. Vacuum melting is a melting and solidification process carried out in an inert environment (typically high vacuum) far below atmospheric pressure. It effectively removes gases and low-boiling-point impurities, prevents oxidation contamination, precisely controls chemical composition, and improves solidification structure and properties.

[0054] As one embodiment of vacuum melting, the temperature of the environment in which the mixed material is located (such as the temperature inside a muffle furnace) is adjusted to 900-1000°C for vacuum melting. For example, the ambient temperature is adjusted to an intermediate temperature at a first speed (such as 5°C / min), which is 2 / 5 to 1 / 2 of the aforementioned vacuum melting temperature (e.g., if the vacuum melting temperature is 1000°C, the intermediate temperature is set to 2 / 5 of the vacuum melting temperature, i.e., 400°C), and held for 1-2 hours. Then, the ambient temperature is adjusted from 400°C to the vacuum melting temperature (such as 1000°C) at a second speed (such as 1°C / min). For example, the ratio of the intermediate temperature to the vacuum melting temperature can be 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, or 0.50.

[0055] Alternatively, the intermediate temperature can be a fixed preset value, such as 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, or 500℃.

[0056] For example, the second speed is less than or equal to 5℃ / min, and can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min; the first speed can be 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min; it can also be 15℃ / min, 20℃ / min, 25℃ / min, or 30℃ / min. Alternatively, the second speed is less than or equal to 10℃ / min, and can be 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min, or 10℃ / min; the first speed can be 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, or 14℃ / min; it can also be 15℃ / min, 20℃ / min, 25℃ / min, or 30℃ / min.

[0057] This two-step heating method prevents excessively rapid heating from causing Te to evaporate violently and resulting in an incomplete reaction. The second heating rate is slower than the first; the higher the temperature, the slower the heating rate, which helps to ensure a more complete reaction. Furthermore, the inventors discovered through experiments that setting the intermediate temperature at a ratio of 2 / 5 to 1 / 2 allows for a more complete reaction compared to setting the intermediate temperature in other ranges.

[0058] In one example, annealing is performed after vacuum melting. Exemplarily, the annealing temperature is 500°C to 600°C, for example, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, or 600°C. Exemplarily, the annealing time is 48h to 72h, for example, 48h, 50h, 52h, 54h, 56h, 58h, 60h, 62h, 64h, 66h, 68h, 70h, or 72h. Annealing is a heat treatment process in which an ingot is heated to a suitable temperature, held at that temperature for a period of time, and then cooled at a certain rate (usually slowly). Annealing can eliminate component segregation (homogenization annealing), relieve internal stress, improve microstructure and processing properties, and prepare an ideal microstructure for subsequent heat treatment.

[0059] Vacuum melting and annealing complement each other, forming a complete process for preparing high-quality ingots: Vacuum melting solves the problems of "purity" and "contamination" from the source, resulting in "clean" ingots with accurate chemical composition and extremely low levels of gases and impurities. Annealing, on the other hand, solves the problems of "inhomogeneity" and "stress" within the ingot, resulting in "useful" ingots with uniform structure, stable performance, and ease of processing.

[0060] S3. Grind the ingot into powder.

[0061] For example, after melting and annealing in step S2, a composition of Sn is obtained. 1-y-z Eu y Bi z The ingot is made of Te + x%MnSb2Te4. Further, the ingot is ground into powder.

[0062] In one example, the ingot is ground using an agate mortar and pestle, and then the powder is sieved through a 160-200 mesh stainless steel sieve to obtain the final powder. Preferably, a 180 mesh sieve (approximately 80-90 micrometers in aperture) is used. Exemplarily, the grinding operation takes 10 minutes, depending on the desired amount of powder obtained.

[0063] Understandably, using an agate mortar and pestle facilitates control over the particle size uniformity of the powder. Using a 160-200 mesh stainless steel sieve allows for easy control of powder particle size, ensuring uniform composition and facilitating the preparation of high-density thermoelectric materials via spark plasma sintering. This avoids or minimizes problems such as excessively large powder sizes (e.g., obtained using a sieve with a mesh size less than 160) or excessively small powder sizes (e.g., obtained using a sieve with a mesh size greater than 200), or uneven powder size (e.g., not using a sieve), which can lead to insufficient sintering. The inventors have experimentally demonstrated that powder obtained using a 180 mesh sieve exhibits superior density after sintering.

[0064] S4. The powder is plasma sintered to obtain a thermoelectric material.

[0065] For example, the powder obtained by grinding in step S3 is loaded into a graphite mold and subjected to spark plasma sintering to obtain the final thermoelectric material.

[0066] In one example, plasma sintering is performed at a temperature of 550–580 °C, a pressure of 40–60 MPa, and a hot-pressing time of 5–10 min. For example, the temperatures are 550 °C, 555 °C, 560 °C, 565 °C, 570 °C, 575 °C, and 580 °C; the pressures are 40 MPa, 42 MPa, 44 MPa, 46 MPa, 48 MPa, 50 MPa, 52 MPa, 54 MPa, 56 MPa, 58 MPa, and 60 MPa; and the times are 5 min, 6 min, 7 min, 8 min, 9 min, and 10 min.

[0067] Plasma sintering is a technique that uses pulsed direct current to rapidly sinter powder and a mold under pressure. The heating rate of plasma sintering is extremely fast (up to hundreds of °C / min), and the entire sintering cycle (from loading to unloading) typically takes only tens of minutes. This greatly suppresses grain coarsening during sintering, which is beneficial for obtaining fine-grained or even nanocrystalline materials, thus significantly improving the material's strength, toughness, and other mechanical properties (following the Hall-Page relation). Under the combined effects of Joule heating generated by the pulsed current, electric field diffusion, and possible plasma activation, the powder particle surface is highly activated, accelerating the diffusion rate. Simultaneously, the applied axial pressure promotes particle rearrangement and plastic flow, enabling plasma sintering to achieve densification close to theoretical density (>99%) at relatively low temperatures and in a shorter time. This is crucial for difficult-to-sinter materials (such as ceramics and intermetallic compounds). The rapid sintering process can "freeze" metastable phases or non-equilibrium structures in the powder, preventing decomposition at prolonged high temperatures. This is extremely advantageous for preparing amorphous alloys, nanocomposites, high-entropy alloys, and other materials that require the preservation of specific structures. In addition, plasma sintering is usually carried out in graphite molds, which can directly sinter blanks with complex shapes and precise dimensions, greatly reducing the amount of subsequent machining and material loss, which is especially important for expensive materials.

[0068] Optionally, after plasma sintering, the final material needs to be removed after cooling and depressurization. For example, after hot pressing, after a preset time (e.g., 5 min to 10 min, which can be 5 min, 6 min, 7 min, 8 min, 9 min, or 10 min), the temperature and pressure of the environment containing the mixed material are reduced to an intermediate temperature and pressure, and held at these temperatures and pressures for 1 min to 5 min (which can be 1.0 min, 1.5 min, 2.0 min, 2.5 min, 3.0 min, 3.5 min, 4.0 min, 4.5 min, or 5.0 min), the ambient temperature is then reduced to room temperature and the pressure is released. After cooling and depressurization are completed, the final material is removed.

[0069] The intermediate temperature can be 0.35 to 0.75 times the plasma sintering temperature, preferably 0.5 to 0.55 times (which can be 0.50, 0.51, 0.52, 0.53, 0.54, or 0.55). For example, the plasma sintering temperature is 550 degrees Celsius, and the intermediate temperature is 300 degrees Celsius. Alternatively, the intermediate temperature can be a fixed preset value, such as 300 degrees Celsius, 310 degrees Celsius, 320 degrees Celsius, 330 degrees Celsius, 340 degrees Celsius, 350 degrees Celsius, 360 degrees Celsius, 370 degrees Celsius, 380 degrees Celsius, 390 degrees Celsius, or 400 degrees Celsius.

[0070] The intermediate pressure is 0.3-0.75 times the plasma sintering pressure, preferably 0.4-0.65 times, and more preferably 0.45-0.5 times. For example, the plasma sintering pressure is 40 MPa, and the intermediate pressure is 25 MPa. Alternatively, the intermediate pressure is a fixed preset value, such as 20 MPa, 21 MPa, 22 MPa, 23 MPa, 24 MPa, 25 MPa, 26 MPa, 27 MPa, 28 MPa, 29 MPa, or 30 MPa.

[0071] Understandably, samples with high vacancy concentrations are brittle, and direct cooling and depressurization can easily cause them to crack due to thermal and mechanical stress. The aforementioned cooling and depressurization scheme can reduce the likelihood of cracking. Furthermore, the inventors have found through experiments that setting the intermediate temperature and pressure in the above proportions allows for a more complete reaction compared to setting them in other ranges.

[0072] Optionally, the depressurization rate during the process of reducing pressure to the intermediate pressure is less than the depressurization rate from the intermediate pressure to complete depressurization; the cooling rate during the process of reducing temperature to the intermediate temperature is less than the cooling rate from the intermediate temperature to room temperature. This allows the material more buffer time under high pressure and high temperature conditions, further reducing thermal and mechanical stress. This, in turn, further reduces the likelihood of sample cracking.

[0073] The following are examples of test results for the thermoelectric materials prepared in each embodiment.

[0074] Figure 1A Powder X-ray diffraction patterns of various embodiments provided in this application are shown. In the experiment, X-ray diffractometer (XRD) was used to analyze the phase structure of the synthesized samples in each embodiment and obtain powder diffraction data. The instrument used Cu Kα as the X-ray source, with an operating voltage of 40 kV, a current of 15 mA, a scanning rate of 10° / min, a scanning angle range of 20°~80°, and a step size of 0.02°.

[0075] Figure 1A In addition to the X-ray diffraction patterns of the sample powders in Examples 1-7, a standard PDF card for SnTe (cubic phase, space group: Fm3m) is also provided as a control. Figure 1AIt can be seen that the XRD diffraction patterns of all sample powders are consistent with the standard PDF card for SnTe, showing diffraction peaks on six crystal planes: (200), (220), (222), (400), (420), and (422), with no obvious redundant diffraction peaks. This indicates that the material still retains the cubic phase (space group: Fm3m) of SnTe even after the absence of impurity phases, i.e., alloyed MnSb2Te4 (optionally, and doped with Eu or Bi). This also shows that the samples all formed good solid solutions. In other words, compared to SnTe, the phase structure of the synthesized samples from Examples 1-7 remains consistent with SnTe after solid solution treatment with MnSb2Te4 (optionally, and doped with Eu or Bi).

[0076] Figure 1B It shows Figure 1A A magnified view of the strongest diffraction peak on the (200) crystal plane. (See image below.) Figure 1B As shown, solid solution MnSb₂Te₄ causes a rightward shift of the diffraction peaks. The higher the proportion of solid solution MnSb₂Te₄, the more the diffraction peaks shift to the right (see and compare the diffraction peaks of Examples 1-3). This indicates that solid solution MnSb₂Te₄ causes lattice contraction in SnTe, i.e., a decrease in the lattice constant. Eu doping causes a leftward shift of the diffraction peaks (see and compare the diffraction peaks of Examples 4 and 5), and Bi doping also causes a leftward shift of the diffraction peaks (see and compare the diffraction peaks of Examples 6 and 7). This indicates that Eu doping and Bi doping cause lattice expansion, i.e., an increase in the lattice constant.

[0077] It is understood that the samples of Examples 1-7 have different compositions compared to SnTe, but the samples of Examples 1-7 still retain the elemental phase of SnTe.

[0078] Figure 2A This paper presents a schematic diagram showing the variation of sample conductivity σ(a) with temperature in various embodiments provided in this application. Figure 2B The diagram illustrates the variation of the Seebeck coefficient S(b) with temperature in various embodiments provided in this application. In the experiment, the conductivity (σ) and Seebeck coefficient (S) of the sample were simultaneously measured using specialized instruments in a helium atmosphere. The measurement temperature range was 300-823 K, and rod-shaped samples with dimensions approximately 2.5 × 2.5 × 10 mm were used. 3 The power factor (PF) is expressed by the formula PF = σS. 2 Calculation. For comparison purposes, Figure 2A and Figure 2B The corresponding measurement data for SnTe (corresponding to the case where x, y, z are all equal to 0) were added as Comparative Example 1.

[0079] from Figure 2AAs can be seen, in Examples 1-7, after alloying MnSb2Te4 with SnTe, the electrical conductivity of the material decreased significantly compared to SnTe, and the lower the temperature, the greater the decrease in conductivity. For example, at a temperature of 300 K, the electrical conductivity of Examples 1-7 ranged from 2167 to 965 S. . cm -1 Within the range, while SnTe (i.e., Comparative Example 1) has a conductivity of 7262 S. . cm -1 For example, at a temperature of 573 K, the conductivity of Examples 1-7 ranges from 1266 to 513 S. . cm -1 Within the range, while SnTe (i.e., Comparative Example 1) has a conductivity of 3058 S. . cm -1 For example, at a temperature of 823 K, the conductivity of Examples 1-7 is between 814 and 520 S. . cm -1 Within the range, while the conductivity of SnTe (i.e., Comparative Example 1) is 1211 S. . cm -1 Therefore, it is evident that the electrical conductivity of the thermoelectric material prepared in this application is significantly lower than that of SnTe (especially at relatively low temperatures). Specifically, the electrical conductivity of the thermoelectric material provided in this application is at least 397 S lower than that of SnTe. . cm -1 .

[0080] Understandably, compared to SnTe, the thermoelectric material provided in this application has a different material composition, namely, it incorporates MnSb₂Te₄ dissolved in SnTe and is doped with Eu and Bi elements. The MnSb₂Te₄ solution introduces a large number of Mn and Sb heteroatomic defects and vacancy defects at the Sn sites in the crystal lattice. This increase in defects leads to a decrease in carrier mobility, which in turn results in a decrease in electrical conductivity. Furthermore, Eu and Bi doping reduces the carrier concentration of the material, which also leads to a decrease in the material's electrical conductivity.

[0081] Comparing the conductivity curves of Example 2 and Example 1 reveals that increasing x from 8 to 10 reduces the material's conductivity. However, the conductivity curves of Example 3 and Example 2 almost overlap, indicating that increasing x from 10 to 12 has little effect on the material's conductivity. Therefore, within a certain range (e.g., x < 10), increasing the proportion of MnSb₂Te₄ can significantly reduce the material's conductivity. However, once x reaches 10, further increases in MnSb₂Te₄ have a significantly lower effect on conductivity reduction compared to when x is less than 10.

[0082] from Figure 2B As can be seen, after alloying MnSb2Te4 with SnTe in each embodiment, the Seebeck coefficient of the material is significantly improved compared to SnTe. That is, the Seebeck coefficient of the thermoelectric material of this application is much greater than that of SnTe. For example, at a temperature of 300 K, the Seebeck coefficients of Examples 1 to 7 are 56.5 to 85.1 μV K. -1 Within the range, while the Seebeck coefficient of SnTe (i.e., Comparative Example 1) is 16.9 μV K. -1 For example, at a temperature of 573 K, the Seebeck coefficients of Examples 1-7 ranged from 120.1 to 197.4 μV K. -1 Within the range, while the Seebeck coefficient of SnTe (i.e., Comparative Example 1) is 53.4 μV K. -1 For example, at a temperature of 823 K, the Seebeck coefficients of Examples 1-7 ranged from 174.2 to 193.2 μV K. -1 Within the range, while the Seebeck coefficient of SnTe (i.e., Comparative Example 1) is 137.0 μV K. -1 Therefore, it can be seen that the Seebeck coefficient of the thermoelectric material prepared in this application is significantly greater than that of SnTe (especially at relatively low temperatures).

[0083] Comparing the Seebeck coefficient curves of Example 2 and Example 1 reveals that increasing x from 8 to 10 improves the Seebeck coefficient of the material. However, the Seebeck coefficient curves of Example 3 and Example 2 almost overlap, indicating that increasing x from 10 to 12 has little effect on the Seebeck coefficient. Therefore, within a certain range (e.g., x < 10), increasing the proportion of MnSb₂Te₄ can significantly improve the Seebeck coefficient. However, after x reaches 10, further increases in MnSb₂Te₄ significantly reduce the improvement in the Seebeck coefficient compared to increases in MnSb₂Te₄ when x is less than 10.

[0084] Understandably, compared to SnTe, the thermoelectric material provided in this application has a different material composition, specifically, it incorporates MnSb₂Te₄ dissolved in SnTe and is doped with Eu and Bi elements. The introduction of Mn, Sb, and vacancies after dissolving MnSb₂Te₄ alters the material's bonding characteristics, leading to changes in the band structure of SnTe. The synergistic optimization of the band structure by Mn, Sb, and vacancies changes the material's electronic transport properties, resulting in an increase in the Seebeck coefficient. Doping with Eu and Bi decreases the carrier concentration, and since the Seebeck coefficient is inversely proportional to the carrier concentration, doping with Eu and Bi also increases the Seebeck coefficient.

[0085] The above analysis of conductivity and Seebeck coefficient shows that x is around 10, which basically reaches the solid solution limit of MnSb2Te4 in SnTe. Therefore, preferably, x is taken as 9.90~10.10, for example, 9.91, 9.92, 9.93, 9.94, 9.95, 9.96, 9.97, 9.98, 9.99, 10, 10.01, 10.02, 10.03, 10.04, 10.05, 10.06, 10.07, 10.08, 10.09, 10.10.

[0086] For example, with x=10, further analysis is performed on SnTe doped with Eu and / or Bi elements. See Examples 4-7. Figure 2A and Figure 2B The corresponding data show that as y and z increase, the electrical conductivity of the thermoelectric material provided in this application gradually decreases, while the Seebeck coefficient gradually increases, indicating that doping with Eu and Bi elements both have a good effect on reducing carrier concentration. For example, at a temperature of 300 K, the Sn provided in Example 4... 0.995 Eu 0.005 Te + 10%MnSb2Te4, conductivity 1511 S . cm -1 The Seebeck coefficient is 73 μV. . K -1 Sn provided in Example 5 0.99 Eu 0.01 Te + 10% MnSb2Te4, conductivity 1301 S . cm -1 The Seebeck coefficient is 78 μV. . K -1 Sn provided in Example 6 0.98 Eu 0.005 Bi 0.015 Te + 10%MnSb2Te4, conductivity 1146 S . cm -1 The Seebeck coefficient is 82 μV. . K -1 Sn provided in Example 7 0.97 Eu 0.005 Bi 0.025 Te + 10%MnSb2Te4, conductivity 965 S . cm -1 The Seebeck coefficient is 85 μV. . K -1 For example, at a temperature of 623 K, the Sn provided in Example 4... 0.995 Eu 0.005Te + 10%MnSb2Te4, conductivity 793S . cm -1 The Seebeck coefficient is 162 μV. . K -1 Sn provided in Example 5 0.99 Eu 0.01 Te + 10%MnSb2Te4, conductivity 669 S . cm -1 The Seebeck coefficient is 175 μV. . K -1 Sn provided in Example 6 0.98 Eu 0.005 Bi 0.015 Te + 10%MnSb2Te4, conductivity 541 S . cm -1 The Seebeck coefficient is 197 μV. . K -1 Sn provided in Example 7 0.97 Eu 0.005 Bi 0.025 Te + 10%MnSb2Te4, conductivity 424 S . cm -1 The Seebeck coefficient is 221 μV. . K -1 .

[0087] Figure 3 The total thermal conductivity κ of the samples provided in the embodiments of this application is shown. tot A schematic diagram showing the change with temperature. In the experiment, a Φ10×1.5 mm... 3 The thermal diffusivity (D) of the disc-shaped sample was measured using the laser scintillation method (NETZSCH LFA467HT instrument, Germany). The total thermal conductivity (κ) of the sample was also measured. tot ) through formula κ tot = D×C p The specific heat capacity (Cp) is calculated using ×ρ, where density (ρ) is determined by Archimedes' displacement method, and specific heat capacity (Cp) is estimated using the Dulong–Petit law. (See also...) Figure 3 After alloying MnSb2Te4 with SnTe, the thermal conductivity of the material decreased significantly compared to SnTe, and the decrease was more pronounced at lower temperatures. For example, at 300 K, the total thermal conductivity of Examples 1-7 ranged from 2.37 to 1.41 W. . m -1. K -1 Within this range, the total thermal conductivity of SnTe (i.e., Comparative Example 1) is 8.27 W. . m -1.K -1 For example, at a temperature of 573 K, the total thermal conductivity of Examples 1-7 is 1.93-1.05 W. . m -1. K -1 Within this range, the total thermal conductivity of SnTe (i.e., Comparative Example 1) is 5.27 W. . m -1. K -1 For example, at a temperature of 823 K, the total thermal conductivity of Examples 1-7 is 1.42-1.39 W. . m -1. K -1 Within this range, the total thermal conductivity of SnTe (i.e., Comparative Example 1) is 2.82 W. . m -1. K -1 Therefore, it can be seen that the total thermal conductivity of the thermoelectric material prepared in this application is much lower than that of SnTe (especially in relatively low temperature environments).

[0088] It is understandable that the thermoelectric material provided in this application, compared to SnTe, has two main drawbacks. Firstly, the reduced electrical conductivity leads to a decrease in electronic thermal conductivity. Secondly, the alloying of MnSb2Te4 forms a uniform solid solution, resulting in numerous lattice defects, including both Mn and Sb impurity atoms, as well as vacancies that strongly scatter phonons (for example, in Example 2, based on the material's chemical composition, the Sn sites in the lattice contain approximately 7.1% Mn, approximately 14.3% Sb, and approximately 7.1% vacancies). This strongly suppresses phonon transport, leading to a decrease in lattice thermal conductivity. The total thermal conductivity consists of both electronic and lattice thermal conductivity. Therefore, the total thermal conductivity of the thermoelectric material provided in this application is significantly lower than that of SnTe.

[0089] Comparing Example 2 with Example 1, it can be seen that increasing x from 8 to 10 can reduce the overall thermal conductivity of the material; comparing Example 3 with Example 2, it can be seen that increasing x from 10 to 12 does not significantly change the overall thermal conductivity of the material. Therefore, it is evident that within a certain range, increasing the proportion of MnSb₂Te₄ can reduce the overall thermal conductivity of the material, but once x reaches 10, further increasing the content of MnSb₂Te₄ has a limited effect on the overall thermal conductivity.

[0090] For example, when x=10, Eu and Bi elements are used for doping, as described in Examples 4-7. Figure 3 Corresponding data: For example, at a temperature of 300 K, Example 4 (Sn 0.995 Eu 0.005 The total thermal conductivity of Te + 10%MnSb2Te4 is 1.75W. . m-1. K -1 Example 5 (Sn) 0.99 Eu 0.01 The total thermal conductivity of Te + 10%MnSb2Te4 is 1.67 W. . m -1. K -1 Example 6 (Sn) 0.98 Eu 0.005 Bi 0.015 The total thermal conductivity of Te + 10%MnSb2Te4 is 1.50 W. . m -1. K -1 Example 7 (Sn) 0.97 Eu 0.005 Bi 0.025 The total thermal conductivity of Te + 10%MnSb2Te4 is 1.42 W. . m -1. K -1 For example, at a temperature of 623 K, Example 4 (Sn 0.995 Eu 0.005 The total thermal conductivity of Te + 10%MnSb2Te4 is 1.34 W. . m -1. K -1 Example 5 (Sn) 0.99 Eu 0.01 The total thermal conductivity of Te + 10%MnSb2Te4 is 1.25 W. . m -1. K -1 Example 6 (Sn) 0.98 Eu 0.005 Bi 0.015 The total thermal conductivity of Te+ 10%MnSb2Te4 is 1.08 W. . m -1. K -1 Example 7 (Sn) 0.97 Eu 0.005 Bi 0.025 The total thermal conductivity of Te + 10%MnSb2Te4 is 1.01 W. . m -1. K -1 This shows that as y and z increase, the overall thermal conductivity of the material further decreases.

[0091] It is understandable that, for the thermoelectric materials of Examples 4-7, due to the doping of Eu and Bi elements, compared to the undoped cases in Examples 1-3, the doping of Eu and Bi elements also introduces point defects in the crystal lattice, thereby suppressing the lattice thermal conductivity. Furthermore, as mentioned above... Figure 2AAs described above, the electrical conductivity of the thermoelectric materials in Examples 4-7 is further reduced compared to Examples 1-3, and this reduction in electrical conductivity leads to a reduction in electronic thermal conductivity. In summary, the thermoelectric materials in Examples 4-7 further reduce the overall thermal conductivity compared to the thermoelectric materials in Examples 1-3.

[0092] Figure 4 The diagram illustrates the variation of the thermoelectric figure of merit ZT with temperature for samples from various embodiments provided in this application. It is understood that the ZT value is a parameter directly evaluating the thermoelectric performance of a material, and can be expressed by the formula ZT = S 2 σT / κ tot The calculation is as follows. In this formula, S is the Seebeck coefficient, σ is the conductivity, T is the absolute temperature, and κ is the electrical conductivity. tot This represents the total thermal conductivity. From... Figure 4 As can be seen, the ZT of the materials provided in this application is significantly improved compared to SnTe. For example, at 823K, the ZT is 0.66 compared to SnTe, while the ZT of Example 2 (SnTe + 10% MnSb2Te4) is increased to 1.31, and the ZT of Example 4 (SnTe + 10% MnSb2Te4) is also increased. 0.995 Eu 0.005 The ZT of Te+10%MnSb2Te4 was increased to 1.36. Although Bi doping caused a slight decrease in ZT at high temperatures, it significantly improved performance at mid- and low-temperature regions. For example, in Example 6 (Sn 0.98 Eu 0.005 Bi 0.015 Te+10%MnSb2Te4) has a significant advantage over SnTe in terms of average ZT across the entire temperature range of 300-823K. For example, at 723K, the ZT of Example 6 reaches a maximum value of 1.37, while the ZT of SnTe is 0.37.

[0093] Understandably, on the one hand, MnSb2Te4 alloying optimizes the electronic band structure of SnTe and introduces a large number of lattice point defects (especially vacancies), thereby significantly improving the Seebeck coefficient, reducing the total thermal conductivity, and thus increasing ZT. On the other hand, doping with Eu and Bi further reduces the carrier concentration of the material, causing the electrical conductivity to continue to decrease, the Seebeck coefficient to increase, and the total thermal conductivity to decrease further, thus leading to a further increase in the ZT value.

[0094] In addition, according to Figure 4The results show that when x=10, the ZT values ​​for y=0.01 and y=0.005 are not significantly different. Therefore, the optimal value of y can be considered to be around 0.005, and can be selected from 0.0045 to 0.0055, for example, 0.0045, 0.0046, 0.0047, 0.0048, 0.0049, 0.0050, 0.0051, 0.0052, 0.0053, 0.0054, 0.0055. Furthermore, with x=10 and y=0.005, the ZT when z is 0.025 is slightly higher in the low-temperature range than the ZT when z is 0.015. However, the ZT when z is 0.025 is significantly lower in the high-temperature range than the ZT when z is 0.015. Therefore, the optimal value of z can be considered to be around 0.015, and can be selected from 0.0145 to 0.0155, for example, 0.0145, 0.0146, 0.0147, 0.0148, 0.0149, 0.0150, 0.0151, 0.0152, 0.0153, 0.0154, 0.0155.

[0095] Figure 5A Four typical samples are shown (Comparative Example 1 (SnTe), Example 2 (SnTe+10%MnSb2Te4), Example 4 (SnTe+10%MnSb2Te4), Example 5 (SnTe+10%MnSb2Te4), Example 6 (SnTe+10%MnSb2Te4), Example 7 (SnTe+10%MnSb2Te4), Example 8 (SnTe+10%MnSb 0.995 Eu 0.005 Te+10%MnSb2Te4), Example 6 (Sn) 0.98 Eu 0.005 Bi 0.015 The room-temperature carrier concentration of Te+10%MnSb2Te4 was determined. The room-temperature carrier concentration of the sample was measured using the van der Bauer method with a Lake Shore Hall effect testing system under a 0.8 T magnetic field. (See also...) Figure 5A The carrier concentration corresponding to Comparative Example 1 (SnTe) is 4.1 × 10⁻⁶. 20 cm -3 The carrier concentration corresponding to Example 2 (SnTe + 10% MnSb2Te4) is 10.2 × 10⁻⁶. 20 cm -3 Example 4 (Sn) 0.995 Eu 0.005 The carrier concentration corresponding to Te+10%MnSb2Te4 is 9.2×10⁻⁶. 20 cm -3 Example 6 (Sn) 0.98 Eu 0.005 Bi 0.015 The carrier concentration corresponding to Te+10%MnSb2Te4 is 7.5×10⁻⁶. 20 cm -3Therefore, alloying with MnSb2Te4 significantly increases the carrier concentration of SnTe, while doping with Eu and Bi elements reduces the carrier concentration of the material, thus optimizing the carrier concentration.

[0096] Figure 5B Four typical samples are shown (Comparative Example 1 (SnTe), Example 2 (SnTe+10%MnSb2Te4), Example 4 (SnTe+10%MnSb2Te4), Example 5 (SnTe+10%MnSb2Te4), Example 6 (SnTe+10%MnSb2Te4), Example 7 (SnTe+10%MnSb2Te4), Example 8 (SnTe+10%MnSb 0.995 Eu 0.005 Te+10%MnSb2Te4), Example 6 (Sn) 0.98 Eu 0.005 Bi 0.015 A comparison of the room-temperature quality factor B of Te+10%MnSb2Te4. The quality factor B reflects the potential of the material's thermoelectric properties and is calculated using the following formula:

[0097] ,

[0098] .

[0099] Where, k B Where is Boltzmann's constant, e is the elementary charge, and m is the t-value. e where μ is the electron mass, h is Planck's constant, and μ is the electron mass. W κ is the weighted mobility. lat σ is the lattice thermal conductivity, σ is the electrical conductivity, S is the Seebeck coefficient, and T is the absolute temperature.

[0100] See Figure 5B The quality factor B for Comparative Example 1 (SnTe) is 0.027, the quality factor B for Example 2 (SnTe+10%MnSb2Te4) is 0.112, and the quality factor B for Example 4 (SnTe+10%MnSb2Te4) is 0.112. 0.995 Eu 0.005 The quality factor B corresponding to Te+10%MnSb2Te4 is 0.113. Example 6 (Sn 0.98 Eu 0.005 Bi 0.015 The quality factor B of the material (Te + 10% MnSb₂Te₄) is 0.100. This demonstrates that alloying MnSb₂Te₄ with SnTe significantly improves the quality factor B, meaning the quality factor B of the thermoelectric material in this application is much greater than that of SnTe. While both Eu and Bi doping reduce the carrier concentration, Eu slightly increases the quality factor B, while Bi slightly decreases it, reflecting the difference in thermoelectric performance regulation between the two elements.

[0101] Figure 6 The average ZT (ZT) of four typical samples in the temperature range of 300-823 K is shown.ave (Comparison). See also Figure 6 The average ZT for Comparative Example 1 (SnTe) was 0.18, the average ZT for Example 2 (SnTe+10%MnSb2Te4) was 0.66, and the average ZT for Example 4 (SnTe+10%MnSb2Te4) was 0.66. 0.995 Eu 0.005 The average ZT corresponding to Te+10%MnSb2Te4 is 0.76. Example 6 (Sn) 0.98 Eu 0.005 Bi 0.015 The average ZT corresponding to Te+10%MnSb2Te4 is 0.88. This shows that with alloying MnSb2Te4 with SnTe, and with Eu and Bi doping, the average ZT increases sequentially from 0.18 for SnTe to 0.66, 0.76, and 0.88. The high average ZT indicates that Sn... 0.98 Eu 0.005 Bi 0.015 The Te+10%MnSb2Te4 sample exhibits high thermoelectric conversion efficiency and potential for waste heat power generation in the medium and low temperature range.

[0102] This application provides a thermoelectric material and its preparation method in the above embodiments. Specifically, the thermoelectric material Sn provided in this application embodiment... 1-y-z Eu y Bi z Te + x%MnSb2Te4 (preferably Sn) 0.98 Eu 0.005 Bi 0.015The thermoelectric figure of merit (ZT) of SnTe (Te+10%MnSb2Te4) reaches 1.37 at 723 K and has an average ZT as high as 0.88 in the 300-823 K temperature range. This high ZT indicates that the material has high thermoelectric conversion efficiency in the mid-to-low temperature range, showing great promise for applications in waste heat power generation. The method for preparing the thermoelectric material provided in this application introduces vacancy engineering through alloying a ternary MnSb2Te4 compound with SnTe, thereby optimizing the thermoelectric transport properties of SnTe. The multi-component substitution of cation sites may produce a cocktail effect, resulting in superior thermoelectric performance and a significant improvement in the material's quality factor (B). Then, the carrier concentration is optimized through two-step doping with Eu and Bi. Eu doping can reduce the carrier concentration without decreasing the material's quality factor (B), while further Bi doping can significantly reduce the carrier concentration, ultimately resulting in a significant improvement in the thermoelectric performance of the SnTe-based material across the entire test temperature range. It is understood that alloying methods with other compounds typically lead to a sharp increase in carrier concentration, which has an adverse effect on thermoelectric performance. Optimization of carrier concentration relies on doping; improper elemental doping can weaken the material's quality factor B, thus limiting the potential for improving thermoelectric performance. Therefore, the two-step doping method for optimizing carrier concentration described in this application is of great significance. Furthermore, the preparation method for the thermoelectric material described in this application has advantages such as simple process, ease of large-scale production, and strong practicality.

[0103] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0104] The parts of this invention not described in detail are well-known in the art. The above embodiments are provided merely for the purpose of describing the invention and are not intended to limit the scope of the invention. The scope of the invention is defined by the appended claims. All equivalent substitutions and modifications made without departing from the spirit and principles of the invention should be covered within the scope of the invention.

Claims

1. A thermoelectric material, characterized in that, The thermoelectric material is based on SnTe, with MnSb2Te4 in solid solution, and doped with Eu and Bi; the thermoelectric material retains the single-phase SnTe. Specifically, lattice defects are introduced into SnTe through solid solution of MnSb₂Te₄ and doping with Eu and Bi; the lattice defects include: The introduction of Mn and Sb impurity atoms and vacancies through solid solution of MnSb₂Te₄; and, The two impurity atoms, Eu and Bi, are introduced by doping with Eu and Bi.

2. The thermoelectric material according to claim 1, characterized in that, The chemical composition of the thermoelectric material is Sn 1-y- z Eu y Bi z Te + x%MnSb2Te4, wherein 0 < x < 12, 0 < y < 0.01, 0 < z < 0.025; Wherein, x is preferably 10 to 12, more preferably 10; y is preferably 0.005 to 0.01, more preferably 0.005; and z is preferably 0.015 to 0.025, more preferably 0.

015.

3. The thermoelectric material according to claim 1 or 2, characterized in that, The electrical conductivity of the thermoelectric material is much lower than that of SnTe; Specifically, lattice defects introduced by solid solution of MnSb2Te4 reduce carrier mobility, thereby reducing electrical conductivity; lattice defects introduced by doping Eu and Bi reduce carrier concentration, thereby reducing electrical conductivity.

4. The thermoelectric material according to any one of claims 1 to 3, characterized in that, The Seebeck coefficient of the thermoelectric material is much higher than that of SnTe; Specifically, the Seebeck coefficient of the thermoelectric material is improved by altering the electronic transport properties through solid solution MnSb2Te4 to introduce lattice defects; the Seebeck coefficient of the thermoelectric material is improved by reducing the carrier concentration through doping Eu and Bi to introduce lattice defects, since the Seebeck coefficient is inversely proportional to the carrier concentration of the material.

5. The thermoelectric material according to any one of claims 1 to 4, characterized in that, The total thermal conductivity of the thermoelectric material is much lower than that of SnTe; The total thermal conductivity includes electronic thermal conductivity and lattice thermal conductivity. The lattice defects introduced by solid solution MnSb2Te4 reduce the electrical conductivity of the thermoelectric material, thereby reducing the electronic thermal conductivity of the thermoelectric material. The lattice defects suppress phonon transport, thereby reducing the lattice thermal conductivity of the thermoelectric material.

6. The thermoelectric material according to any one of claims 1 to 5, characterized in that, The thermoelectric figure of merit of the aforementioned thermoelectric material is much higher than that of SnTe; Among them, the Seebeck coefficient is improved by solid solution of MnSb2Te4 and the lattice defects introduced by doping Eu and Bi, and the total thermal conductivity is reduced, thereby improving the thermoelectric figure of merit.

7. A method for preparing a thermoelectric material according to any one of claims 1 to 6, characterized in that, Includes the following steps: S1, according to the chemical formula Sn 1-y-z Eu y Bi z The stoichiometric ratio of Te + x% MnSb2Te4 mixes the elements Sn, Te, Mn, Sb, Eu, Bi; S2. The mixed material is vacuum melted and annealed to obtain a composition of Sn. 1-y-z Eu y Bi z Ingots of Te + x%MnSb2Te4; S3. Grind the ingot into powder; wherein, the ingot is ground using an agate mortar and pestle, and the powder is obtained by sieving through a 160-200 mesh stainless steel sieve. S4. The powder is subjected to spark plasma sintering to obtain the thermoelectric material; In step S2, during the vacuum melting process, the ambient temperature of the mixed material is adjusted to an intermediate temperature at a first speed and held for 1 to 2 hours; then, the intermediate temperature is adjusted to the vacuum melting temperature at a second speed, wherein the vacuum melting temperature is 900 to 1000°C.

8. The method for preparing the thermoelectric material according to claim 7, characterized in that, In step S2, the vacuum melting temperature is 900~1000℃ and the vacuum melting time is 10~20h; the annealing temperature is 600℃ and the annealing time is 48h~72h.

9. The method according to claim 8, characterized in that, The first speed is greater than the second speed, and the intermediate temperature is a preset temperature, or the intermediate temperature is 2 / 5 to 1 / 2 times the temperature of the vacuum melting.

10. The method according to any one of claims 7 to 9, characterized in that, In step S4, the discharge plasma sintering is carried out at a temperature of 550~580 ℃, a pressure of 40~60 MPa, and a hot pressing time of 5~10 min. S4, wherein the powder is subjected to discharge plasma sintering to obtain the thermoelectric material, includes: After the powder is subjected to discharge plasma sintering, the temperature and pressure of the current environment are reduced to the intermediate temperature and pressure, and then the temperature and pressure are maintained for 1 to 5 minutes. The temperature of the current environment is reduced to room temperature and the pressure is released in order to remove the thermoelectric material from the current environment; Wherein, the intermediate temperature is a preset temperature, or the intermediate temperature is 0.35 to 0.75 times the plasma sintering temperature; the intermediate pressure is a preset pressure, or the intermediate pressure is 0.35 to 0.75 times the plasma sintering pressure.

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