An alkali metal fluoride-doped p-type mg3sb2-based thermoelectric material and a preparation method thereof
By using alkali metal fluoride dopants combined with vacuum solid-state sintering and rapid hot pressing processes, the problems of low conductivity and uneven doping in P-type Mg3Sb2-based thermoelectric materials were solved, achieving efficient and uniform doping effects and improving the overall thermoelectric performance of the materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ANHUI UNIV
- Filing Date
- 2023-07-12
- Publication Date
- 2026-07-07
AI Technical Summary
In the existing technology, P-type Mg3Sb2-based thermoelectric materials have low electrical conductivity and poor ZT performance. Alkali metal element doping has problems such as complicated operation, unevenness and pollution. Traditional high-energy ball milling process is difficult to achieve effective doping.
P-type Mg3Sb2-based thermoelectric materials were prepared by using alkali metal fluorides as dopants and through vacuum solid-state sintering combined with rapid hot pressing. This method avoids the use of elemental alkali metals and achieves uniform doping and efficient preparation of alkali metal elements.
It improves electrical conductivity and Seebeck coefficient, reduces thermal conductivity, and significantly enhances overall thermoelectric performance, avoiding the drawbacks of traditional methods and achieving efficient and uniform doping effects.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of thermoelectric materials, specifically relating to an alkali metal fluoride-doped P-type Mg3Sb2-based thermoelectric material and its preparation method. Background Technology
[0002] Thermoelectric materials are functional materials that can convert heat energy and electrical energy into each other. Their performance mainly depends on the dimensionless thermoelectric figure of merit ZT, defined as ZT = S 2 σT / κ, where σ is the conductivity, S is the Seebeck coefficient, and S 2 σ is also known as the power factor (PF), and T is the thermodynamic temperature in the Kelvin function. κ is the thermal conductivity, expressed by the formula κ = DρC. p The calculation yields the result, where D is the thermal diffusivity, ρ is the sample density, and C is the density of the sample. p For isobaric specific heat, according to the Dulong-Petty formula C p =3nR / M. A high ZT value implies higher energy conversion efficiency and potentially higher output power, which is the core goal of thermoelectric material research.
[0003] Mg3Sb2-based thermoelectric materials have become a research hotspot in recent years due to their low cost and excellent thermoelectric performance. Among them, p-type Mg3Sb2-based thermoelectric materials suffer from low conductivity and poor ZT performance due to their low carrier concentration. Current research on p-type Mg3Sb2-based thermoelectric materials focuses on the regulation of electrical properties by doping Mg sites with +1 valence alkali metals such as Li, Na, and K to improve conductivity and thus increase ZT values. Currently, the Li, Na, and K dopants used for doping are usually their corresponding elemental metals. However, this type of alkali metal doping has many drawbacks. Taking Na doping as an example, firstly, elemental Na has low hardness and a soft texture, often existing in large blocks, making it impossible to prepare powder reagents, which is detrimental to controlling weighing accuracy and doping uniformity. Secondly, elemental Na is chemically very reactive, readily reacting with water and oxygen. Therefore, it is usually stored in kerosene to isolate it from air, and when used, it must be taken out in an inert atmosphere glove box with strictly controlled water and oxygen content, and then fresh Na blocks / shavings of the target mass must be cut for doping experiments. This process is time-consuming and laborious, and it is easy to introduce impurities such as oil, which brings great inconvenience to the experiment.
[0004] On the other hand, when doping Mg3Sb2-based thermoelectric materials with alkali metals, mechanical alloying is usually used. Mg, Sb, and elemental alkali metals are placed in a high-energy ball mill for high-speed mechanical grinding, thereby undergoing an alloying reaction to directly generate alkali metal-doped Mg3Sb2 [J Shuai, Y Wang, HS Kim, Thermoelectric properties of Na-doped Zintl compound:Mg3-x Na x [Sb2[J]. Acta Mater 2015,93,187-193.]. However, this method also has obvious drawbacks. For example, the raw material powder is prone to adhere to the surface of the grinding balls or the inner wall of the grinding jar during the grinding process, causing the product composition to deviate from the predetermined stoichiometric ratio, which is not conducive to controlling the specific elemental composition content of the sample; especially for doped samples, since the dopant content is usually small, even slight adhesion loss may cause a significant reduction in the concentration of dopant elements in the final product, making it impossible to achieve effective doping. In addition, the contamination problem of the final product caused by the high-speed and violent collision between the grinding balls and grinding jar and the raw material powder cannot be ignored. Therefore, the search for a simple and efficient alkali metal doped Mg3Sb2-based thermoelectric material and its preparation method is of great significance to the research of P-type Mg3Sb2-based thermoelectric materials. Summary of the Invention
[0005] The technical problem to be solved by the present invention is to provide an alkali metal fluoride-doped P-type Mg3Sb2-based thermoelectric material that exhibits high electrical conductivity and Seebeck coefficient and low thermal conductivity, and has excellent overall thermoelectric performance, in order to overcome the shortcomings of the prior art.
[0006] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:
[0007] An alkali metal fluoride-doped p-type Mg3Sb2 thermoelectric material, with the chemical composition formula: Mg 3-y Cd y Sb2-x%AF; where Mg 3-y Cd y Sb2 represents the thermoelectric material matrix, AF indicates the dopant alkali metal fluoride, and x%AF indicates the dopant AF in the thermoelectric material matrix Mg. 3-y Cd y The doping mass percentage in Sb2 is 0 < x ≤ 2 and 0 ≤ y ≤ 1.
[0008] According to the above scheme, the AF is selected from one or more of LiF, NaF, KF, RbF or CsF.
[0009] The alkali metal fluoride-doped p-type Mg3Sb2 thermoelectric material of this invention exhibits an electrical conductivity of 42700–14000 S / m in the temperature range of 303–773 K. -1 The Seebeck coefficient is 90–210 μV K. -1 The power factor is 2.3–8.5 μW cm⁻¹. -1 K -2 The thermal conductivity is 1.76–0.73 W / m. -1 K -1The ZT value is 0.04–0.91. When the chemical composition is Mg3Sb2-1%NaF, the conductivity is 23800–14000 S m in the temperature range of 303–773 K. -1 The Seebeck coefficient is 98–210 μVK. -1 The power factor is 2.3–6.4 μW cm⁻¹. -1 K -2 The thermal conductivity is 1.76–0.85 W / m. -1 K -1 ZT values range from 0.04 to 0.56. The chemical composition formula is Mg. 2.5 Cd 0.5 When Sb²⁻¹% NaF is present, the conductivity is 42700–20400 S m in the temperature range of 303–773 K. -1 The Seebeck coefficient is 90–204 μV K. -1 The power factor is 3.4–8.5 μW cm⁻¹. -1 K -2 The thermal conductivity is 1.11–0.73 W / m. -1 K -1 The ZT value is 0.09 to 0.91.
[0010] This invention also provides a method for preparing the above-mentioned alkali metal fluoride-doped p-type Mg3Sb2-based thermoelectric material. Using alkali metal fluorides as alkali metal dopants, the method employs vacuum solid-state sintering combined with rapid hot pressing to prepare the alkali metal fluoride-doped Mg3Sb2-based thermoelectric material. This avoids the drawbacks of using elemental alkali metal dopants and achieves effective doping of alkali metal elements. Specifically, the method includes the following steps:
[0011] (1) According to Mg 3-y Cd y The stoichiometric ratio of each element in Sb2-x%AF is obtained by weighing Mg powder, Sb powder, Cd powder and AF powder as raw materials, mixing them evenly in an anhydrous and oxygen-free environment (mainly to avoid oxidation of Mg powder and hydrolysis of AF), cold pressing them into blocks, placing them in an alumina crucible and vacuum sealing them in a quartz tube.
[0012] (2) Heat the quartz tube described in step (1) to 950-1000K for high-temperature solid-state sintering, hold for 100-170h, then cool to room temperature and remove the product from the quartz tube.
[0013] (3) The product obtained in step (2) is ground into powder and then vacuum hot-pressed and sintered to obtain alkali metal fluoride doped P-type Mg3Sb2-based thermoelectric material.
[0014] According to the above scheme, the heating and cooling rates in step (2) are both 1–5 K min. -1.
[0015] According to the above scheme, in step (3), the temperature of vacuum hot pressing sintering is 773-1073K, the sintering pressure is 50-80MPa, and the sintering time is 10-30min.
[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0017] 1. The P-type Mg3Sb2-based thermoelectric material of the present invention exhibits high electrical conductivity and Seebeck coefficient as well as low thermal conductivity, and has excellent overall thermoelectric performance; moreover, it has a pure phase and high density.
[0018] 2. This invention uses alkali metal fluoride (AF) powder as a dopant, providing an alkali metal source and achieving the effect of alkali metal element doping. This avoids the drawbacks of using elemental alkali metals as dopant, achieving effective doping of alkali metal elements. In existing technologies, when doping p-type Mg3Sb2-based thermoelectric materials, the valence of the dopant element is usually considered. Alkali metal doping provides holes, thus improving electrical performance. Theoretically, fluorine (F) doping would provide electrons, thus reducing electrical performance. However, the inventors discovered that F is not uniformly distributed in the matrix, but reacts with Mg to form micron-sized MgF2. This is likely due to F's extremely high electronegativity, which allows it to react with cations. Simultaneously, MgF2 consumes Mg in the matrix, increasing the Mg vacancy content, improving electrical performance, and also reducing thermal conductivity, thereby increasing the ZT value. Therefore, the inventors' use of fluoride (AF) instead of elemental alkali metals as the dopant source for preparing p-type Mg3Sb2-based thermoelectric materials is a novel technical approach that improves overall thermoelectric performance, representing an unexpected technical effect.
[0019] 3. This invention adopts a vacuum solid-state sintering combined with rapid hot pressing process, which avoids the drawbacks of using traditional high-energy ball milling process, avoids the loss of matrix and dopant, makes the doping efficiency higher, and makes the preparation process simpler and more efficient. Attached Figure Description
[0020] Figure 1 X-ray diffraction patterns of the thermoelectric materials prepared in Examples 1, 2, and Comparative Examples 1 and 2;
[0021] Figure 2 The elemental distribution diagram of the thermoelectric material prepared in Example 1;
[0022] Figure 3 This is a graph showing the change in electrical conductivity (σ) as a function of temperature for the thermoelectric materials prepared in Examples 1, 2, and Comparative Examples 1 and 2.
[0023] Figure 4This is a graph showing the Seebeck coefficient (S) of the thermoelectric materials prepared in Examples 1, 2, and Comparative Examples 1 and 2 of the present invention as a function of temperature.
[0024] Figure 5 This is a graph showing the power factor (PF) of the thermoelectric materials prepared in Examples 1, 2, and Comparative Examples 1 and 2 of the present invention as a function of temperature.
[0025] Figure 6 This is a graph showing the thermal conductivity (κ) of the thermoelectric materials prepared in Examples 1, 2, and Comparative Examples 1 and 2 of the present invention as a function of temperature.
[0026] Figure 7 The graph shows the thermoelectric figure of merit (ZT) of the thermoelectric materials prepared in Examples 1, 2, and Comparative Examples 1 and 2 of the present invention as a function of temperature. Detailed Implementation
[0027] To further understand the present invention, the following embodiments are provided for detailed description of the implementation schemes of the present invention, but they should not be construed as limiting the scope of protection of the present invention.
[0028] Compare with Example 1
[0029] A method for preparing Na-doped Mg3Sb2 thermoelectric material, the specific steps of which are as follows:
[0030] Step 1: Weigh Mg powder, Sb powder and Na block as raw materials in an argon atmosphere glove box with water and oxygen content below 1ppm, according to the stoichiometric ratio of each element in Mg3Sb2-1% Na. Then mix the Mg powder and Sb powder evenly in an agate mortar.
[0031] Step 2: The Mg and Sb mixture powder obtained in Step 1 is cold-pressed with Na block into a bulk material, then placed in an alumina crucible and vacuum-sealed inside a quartz tube; next, the quartz tube is placed in a pit furnace for high-temperature solid-state sintering reaction. The conditions for the high-temperature solid-state sintering reaction are: 1 K min -1 The temperature was increased to 973 K at a rate of [missing information], held for 120 h, and then increased at a rate of 1 K min [missing information]. -1 The rate at which it decreases to room temperature;
[0032] Step 3: Take the product obtained from the reaction in Step 2 out of the quartz tube, grind it into powder in an agate mortar, and then perform vacuum hot pressing sintering at a sintering temperature of 873K, a sintering pressure of 80MPa, and a sintering time of 20min to obtain a high-density Mg3Sb2-1% Na bulk thermoelectric material, namely Na-doped Mg3Sb2 thermoelectric material.
[0033] The XRD diffraction pattern of the Mg3Sb2-1% Na thermoelectric material prepared in this comparative example retains the Mg3Sb2 phase. Figure 1 The conductivity at 303–773 K is 25950–14000 S / m. -1 ( Figure 3 The Seebeck coefficient is 96–204 μV K. -1 ( Figure 4 The power factor is 2.4–5.8 μW cm⁻¹. -1 K -2 ( Figure 5 Thermal conductivity is 1.95–0.92 W / m. -1 K -1 ( Figure 6 ZT values range from 0.03 to 0.49. Figure 7 ).
[0034] Compare with Example 2
[0035] A method for preparing a Na and Cd co-doped Mg3Sb2 thermoelectric material, the specific steps of which are as follows:
[0036] Step 1: According to Mg 2.5 Cd 0.5 The stoichiometric ratio of each element in Sb2-1% Na was determined by weighing Mg powder, Cd powder, Sb powder, and Na block as raw materials in an argon atmosphere glove box with water and oxygen content below 1 ppm, and then mixing the Mg powder, Cd powder, and Sb powder evenly in an agate mortar.
[0037] Step 2: The Mg, Cd, and Sb mixture powder obtained in Step 1 is cold-pressed with the Na block into a bulk material, then placed in an alumina crucible and vacuum-sealed inside a quartz tube. Next, the quartz tube is placed in a pit furnace for a high-temperature solid-state sintering reaction. The conditions for the high-temperature solid-state sintering reaction are: 1 K min... -1 The temperature was increased to 973 K at a rate of [missing information], held for 120 h, and then increased at a rate of 1 K min [missing information]. -1 The rate at which it decreases to room temperature;
[0038] Step 3: Remove the product obtained in Step 2 from the quartz tube, grind it into powder in an agate mortar, and then perform vacuum hot pressing sintering at a sintering temperature of 873 K, a sintering pressure of 80 MPa, and a sintering time of 20 min to obtain high-density Mg. 2.5 Cd 0.5 Sb2-1% Na bulk thermoelectric material, namely Na and Cd co-doped Mg3Sb2 thermoelectric material.
[0039] The Mg prepared in this comparative example 2.5 Cd 0.5The XRD diffraction pattern of the Sb2-1% Na thermoelectric material retains the Mg3Sb2 phase. Figure 1 The conductivity at 303–773 K is 40700–19700 S / m. -1 ( Figure 3 The Seebeck coefficient is 90–200 μVK. -1 ( Figure 4 The power factor is 3.2–7.9 μW cm⁻¹. -1 K -2 ( Figure 5 Thermal conductivity is 1.13–0.76 W / m. -1 K -1 (Appendix) Figure 6 ZT value is 0.08~0.82 ( Figure 7 ).
[0040] Example 1
[0041] A method for preparing an alkali metal fluoride-doped p-type Mg3Sb2-based thermoelectric material, the specific steps of which are as follows:
[0042] Step 1: According to the stoichiometric ratio of each element in Mg3Sb2-1% NaF, weigh Mg powder, Sb powder and NaF powder as raw materials in an argon atmosphere glove box with water and oxygen content of less than 1ppm, and then mix them evenly in an agate mortar.
[0043] Step 2: The powder mixture obtained in Step 1 is cold-pressed into a block, then placed in an alumina crucible and vacuum-sealed inside a quartz tube; next, the quartz tube is placed in a pit furnace for a high-temperature solid-state sintering reaction. The conditions for the high-temperature solid-state sintering reaction are: 1 K min -1 The temperature was increased to 973 K at a rate of [missing information], held for 120 h, and then increased at a rate of 1 K min [missing information]. -1 The rate at which it decreases to room temperature;
[0044] Step 3: Remove the product obtained in Step 2 from the quartz tube, grind it into powder in an agate mortar, and then perform vacuum hot pressing sintering at a sintering temperature of 873K, a sintering pressure of 80MPa, and a sintering time of 20min to obtain a high-density Mg3Sb2-1% NaF bulk thermoelectric material, namely, an alkali metal fluoride-doped P-type Mg3Sb2-based thermoelectric material.
[0045] like Figure 1 As shown, the Mg3Sb2-1% NaF thermoelectric material prepared in Example 1 retains the Mg3Sb2 phase; Figure 2The cross-sectional elemental distribution diagram shows that the sample surface is dense, without cracks or pores, with a density of 95% or higher. Na is evenly distributed, and Mg is also enriched in areas where F is abundant, indicating the formation of MgF2. The generated MgF2 secondary phase can enhance phonon scattering, thereby reducing thermal conductivity, while the doping of alkali metal fluorides significantly improves electrical properties, ultimately achieving excellent thermoelectric figure of merit.
[0046] like Figure 3-7 As shown, the Mg3Sb2-1% NaF thermoelectric material prepared in Example 1 has an electrical conductivity of 23800-14000 Sm at 303-773 K. -1 The Seebeck coefficient is 98–210 μV K. -1 The power factor is 2.3–6.4 μW cm⁻¹. -1 K -2 Thermal conductivity is 1.76–0.85 W / m. -1 K -1 The ZT value is 0.04 to 0.56.
[0047] Example 1 significantly improved the electrical conductivity and power factor by doping with alkali metal fluorides. The thermal conductivity decreased by 8.4% compared to Control Example 1 due to the enhanced phonon scattering of MgF2. The highest ZT value was 0.56, which was 14% higher than the highest ZT value of 0.49 in Control Example 1.
[0048] Example 2
[0049] A method for preparing an alkali metal fluoride-doped p-type Mg3Sb2-based thermoelectric material, the specific steps of which are as follows:
[0050] Step 1: According to Mg 2.5 Cd 0.5 The stoichiometric ratio of each element in Sb2-1% NaF was determined by weighing Mg powder, Sb powder, Cd powder and NaF powder as raw materials in an argon atmosphere glove box with water and oxygen content below 1 ppm, and then mixing them evenly in an agate mortar.
[0051] Step 2: The powder mixture obtained in Step 1 is cold-pressed into a block, then placed in an alumina crucible and vacuum-sealed inside a quartz tube; next, the quartz tube is placed in a pit furnace for a high-temperature solid-state sintering reaction. The conditions for the high-temperature solid-state sintering reaction are: 1 K min -1 The temperature was increased to 973 K at a rate of [missing information], held for 120 h, and then increased at a rate of 1 K min [missing information]. -1 The rate at which it decreases to room temperature;
[0052] Step 3: Remove the product obtained in Step 2 from the quartz tube, grind it into powder in an agate mortar, and then perform vacuum hot pressing sintering at a sintering temperature of 873K, a sintering pressure of 80MPa, and a sintering time of 20min to obtain high-density Mg. 2.5 Cd 0.5 Sb2-1% NaF bulk thermoelectric material, namely, alkali metal fluoride-doped P-type Mg3Sb2-based thermoelectric material.
[0053] The Mg prepared in this embodiment 2.5 Cd 0.5 Sb2-1% NaF thermoelectric material retains the Mg3Sb2 phase ( Figure 1 The conductivity at 303–773 K is 42700–20400 S / m. -1 ( Figure 3 The Seebeck coefficient is 90–204 μV K. -1 ( Figure 4 The power factor is 3.4–8.5 μW cm⁻¹. -1 K -2 ( Figure 5 Thermal conductivity is 1.11–0.73 W / m. -1 K -1 ( Figure 6 ZT value is 0.09~0.91 (); Figure 7 ).
[0054] The conductivity and power factor of Example 2 compared to Control Example 2 (Mg) 2.5 Cd 0.5 The ZT values of Sb2-1% Na samples all showed improvement; the thermal conductivity decreased slightly, and the final maximum ZT value was 0.91, which was about 11% higher than the highest ZT value of 0.82 in control example 2.
[0055] from Figure 3 It can be seen that NaF doping significantly improves conductivity, making it comparable to that of the Na-doped sample across the entire temperature range. From... Figure 4 It can be seen that the Seebeck coefficients of the NaF-doped and Na-doped samples are basically the same. Based on the optimization of conductivity and Seebeck coefficient, from Figure 5 It can be seen that the Mg3Sb2-1% NaF sample and Mg 2.5 Cd 0.5 The power factors of the Sb2-1% NaF samples were all improved compared to those of the Na-doped samples. Figure 6It can be seen that, due to the enhanced phonon scattering, the thermal conductivity of NaF-doped material is lower than that of Na-doped material. Ultimately, through dual optimization of electrical and thermal properties, the maximum ZT figure of merit of the NaF-doped Mg3Sb2-1% NaF thermoelectric material reached 0.56, a 14% improvement compared to the Na-doped Mg3Sb2-1% Na sample at the same temperature. NaF and Cd co-doped Mg... 2.5 Cd 0.5 The ZT figure of merit for Sb²⁻¹NaF thermoelectric material reached a maximum of 0.91, which is significantly higher than that of Na and Cd co-doped Mg at the same temperature. 2.5 Cd 0.5 The Sb2-1% Na sample showed an 11% increase.
[0056] In addition to NaF used in the examples, when other alkali metal fluorides are used as doping sources in the P-type Mg3Sb2 system, the present invention can also achieve the effects of increasing carrier concentration by doping with alkali metals and generating MgF2 to reduce thermal conductivity, thereby improving the overall thermoelectric performance to a certain extent.
[0057] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.
Claims
1. An alkali metal fluoride-doped p-type Mg3Sb2 thermoelectric material, characterized in that... The chemical composition formula is Mg 3- y Cd y Sb2-x%AF; where Mg 3-y Cd y Sb2 represents the thermoelectric material matrix, AF indicates the dopant alkali metal fluoride, and x%AF indicates the dopant AF in the thermoelectric material matrix Mg. 3-y Cd y The doping mass percentage in Sb2 is 0 < x ≤ 2 and 0 ≤ y ≤ 1.
2. The alkali metal fluoride-doped p-type Mg3Sb2 thermoelectric material according to claim 1, characterized in that... AF is selected from one or more of LiF, NaF, KF, RbF or CsF.
3. The alkali metal fluoride-doped p-type Mg3Sb2 thermoelectric material according to claim 1, characterized in that... The conductivity is 42700–14000 Sm in the temperature range of 303–773 K. -1 The Seebeck coefficient is 90–210 μVK. -1 The power factor is 2.3–8.5 μW cm⁻¹. -1 K -2 The thermal conductivity is 1.76–0.73 W / m. -1 K -1 The ZT value is 0.04 to 0.
91.
4. The alkali metal fluoride-doped P-type Mg3Sb2 thermoelectric material according to claim 1, characterized in that... When the chemical composition is Mg3Sb2-1%NaF, the electrical conductivity is 23800–14000 Sm in the temperature range of 303–773 K. -1 The Seebeck coefficient is 98–210 μV K. -1 The power factor is 2.3–6.4 μW cm⁻¹. -1 K -2 The thermal conductivity is 1.76–0.85 W / m. -1 K -1 ZT values range from 0.04 to 0.56; the chemical composition formula is Mg 2.5 Cd 0.5 When Sb²⁻ + 1% NaF is present, the conductivity is 42700–20400 Sm in the temperature range of 303–773 K. -1 The Seebeck coefficient is 90–204 μV K. -1 The power factor is 3.4–8.5 μW cm⁻¹. -1 K -2 The thermal conductivity is 1.11–0.73 W / m. -1 K -1 The ZT value is 0.09 to 0.
91.
5. The method for preparing the alkali metal fluoride-doped p-type Mg3Sb2-based thermoelectric material according to any one of claims 1 to 4, characterized in that... It includes the following steps: (1) According to Mg 3-y Cd y The stoichiometric ratio of each element in Sb2-x%AF is obtained by weighing Mg powder, Sb powder, Cd powder and AF powder as raw materials, mixing them evenly in an anhydrous and oxygen-free environment, cold pressing them into blocks, placing them in an alumina crucible and vacuum sealing them in a quartz tube. (2) Heat the quartz tube described in step (1) to 950-1000K for high-temperature solid-state sintering, hold for 100-170h, then cool to room temperature and remove the product from the quartz tube. (3) The product obtained in step (2) is ground into powder and then vacuum hot-pressed and sintered to obtain alkali metal fluoride doped P-type Mg3Sb2-based thermoelectric material.
6. The method for preparing the alkali metal fluoride-doped p-type Mg3Sb2-based thermoelectric material according to claim 5, characterized in that... The vacuum hot pressing sintering temperature is 773–1073 K, the sintering pressure is 50–80 MPa, and the sintering time is 10–30 min.
7. The method for preparing alkali metal fluoride-doped p-type Mg3Sb2-based thermoelectric materials according to claim 5, characterized in that... In step (2), the heating and cooling rates are both 1–5 K min. -1 .