A high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range and its preparation method.

Abstract

This invention relates to the field of thermoelectric materials technology, specifically to a method for preparing a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range. The method is characterized in that the N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material comprises Co magnetic nanoparticles and Mg... 3.2 Sb 1.5 Bi 0.49 Te 0.01 It is composed of thermoelectric materials and is denoted as xCo / Mg. 3.2 Sb 1.5 Bi 0.49 Te 0.01 Where x represents Co and Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 The mass percentage ranges from 0.1% to x, which is less than or equal to 0.4%. This invention uses Mg3Sb2-based thermoelectric material obtained by vacuum solid-state sintering as a substrate. This substrate is then mechanically mixed uniformly with Co magnetic nanoparticles in a mortar and composited using a rapid hot-pressing process. Afterward, it is machined into a regular shape using diamond wire cutting and then annealed in a Mg atmosphere to compensate for the Mg volatilization during heat treatment. The resulting N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material exhibits a high Seebeck coefficient and low lattice thermal conductivity, demonstrating excellent overall thermoelectric performance. This provides more possibilities for the application of mid-temperature thermoelectric materials in waste heat recovery and other fields.

Description

Technical Field

[0001] This invention relates to the field of thermoelectric materials technology, specifically to a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range and its preparation method. Background Technology

[0002] Thermoelectric materials can effectively utilize waste heat from low-temperature temperature differences in power generation, expanding the sources of clean energy. In refrigeration, they can achieve precise, localized, vibration-free temperature control, avoiding the environmental hazards of traditional refrigerants. Both applications demonstrate their high-efficiency and environmentally friendly energy conversion characteristics, which have dual positive significance in alleviating energy shortages and reducing thermal pollution. The power generation efficiency of both thermoelectric generators and thermoelectric coolers is related to the dimensionless thermoelectric figure of merit (zT), and its level comprehensively reflects the performance of thermoelectric materials, defined as zT = S. 2 σT / κ represents the material's Seebeck coefficient, σ is its electrical conductivity, and κ is its total thermal conductivity, which is derived from the electronic thermal conductivity κ. e and lattice thermal conductivity κ L The thermoelectric material consists of two parts, where T is the absolute temperature. To increase the zT value of a thermoelectric material, α and σ need to be increased while κ needs to be decreased. However, these parameters are coupled to each other through band structure and scattering mechanisms, so it is necessary to synergistically control the electrothermal transport parameters to appropriately increase the zT value of the thermoelectric material.

[0003] Mg3Sb2-based materials are a newly emerging system in recent years. Composed of Mg and Sb elements, which are abundant on Earth, they are inexpensive and environmentally friendly. More importantly, their complex crystal structure and inherently low lattice thermal conductivity give them excellent "phonon glass" properties. Furthermore, through appropriate doping or modifications to the preparation process, they can achieve good "electronic crystal" conductivity. Therefore, Mg3Sb2 is considered a highly promising next-generation mid-temperature thermoelectric material. Besides conventional methods for optimizing thermoelectric performance, magnetism has been introduced into the thermoelectric field as a new degree of freedom in recent years, and its novel thermo-electromagnetic coupling effect has been widely studied. However, current research mainly focuses on Bi2Te3-based materials, with relatively little research on Mg3Sb2-based materials.

[0004] In view of the shortcomings in the above-mentioned research fields, this invention was finally obtained after a long period of research and practice. Summary of the Invention

[0005] The purpose of this invention is to provide a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range and its preparation method, by using Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01Magnetic nanoparticles are introduced into the matrix material, and the magnetic effect and doping effect of the magnetic nanoparticles are used to synergistically optimize the electrical and thermal transport properties of the matrix material, so as to fill the gaps in N-type Mg3Sb2-based magnetic nanocomposites.

[0006] In a first aspect, the present invention provides a method for preparing a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range, comprising the following steps: (1) Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 Thermoelectric materials and nano-Co magnetic particles are mechanically ground uniformly in a mortar to obtain magnetic nanocomposite powder; (2) Load the powder that has been ground evenly in step (1) into a graphite mold; (3) The mold assembled in step (2) is sintered under vacuum using a rapid hot pressing method to obtain Mg3Sb2-based magnetic nanocomposite thermoelectric material. (4) The product obtained in step (3) is cut and polished with sandpaper to obtain long strips and arc-shaped blocky Mg3Sb2-based thermoelectric materials. These are placed in an alumina crucible and wrapped with Mg shavings, then sealed in a quartz tube under vacuum. Annealing is performed in a muffle furnace. After annealing, stable N-type Mg3Sb2-based magnetic nanocomposite thermoelectric materials are obtained.

[0007] Preferably, the nano-Co magnetic particles described in (1) are combined with Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 The mass percentage of thermoelectric materials is 0.1% to 0.4%, and the mechanical grinding time is 10 min.

[0008] Preferably, the graphite mold described in (2) has an outer diameter of 50 mm and an inner diameter of 13 mm, and the powder needs to be divided into two parts with a mass of 1.4 g and 1.15 g, which are separated by carbon paper and carbon sheet during sample loading.

[0009] Preferably, the sintering temperature in (3) is 873 K, the sintering pressure is 80 MPa, and the sintering time is 20 min.

[0010] Preferably, the quartz tube described in (5) has an outer diameter of 20 mm and an inner diameter of 17 mm, and the annealing process is carried out in a muffle furnace at 7 K min. -1 The temperature was increased to 873 K at a rate of [missing information], held for 1 h, and then increased at 7 K min [missing information]. -1 The rate at which it decreases to room temperature.

[0011] Secondly, the present invention provides a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range, wherein the N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material is obtained by the above preparation method.

[0012] Preferably, the N-type Mg3Sb2 magnetic nanocomposite thermoelectric material is composed of Co magnetic nanoparticles and Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 Thermoelectric materials are composites, and the N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material is denoted as xCo / Mg. 3.2 Sb 1.5 Bi 0.49 Te 0.01 Where x represents Co and Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 The mass percentage ranges from 0.1% to x and from 0.4%.

[0013] Preferably, x = 0.3%.

[0014] The technical effects and advantages provided by the present invention in the above technical solution are as follows: 1. The Mg3Sb2-based thermoelectric material described in this invention has a high quality factor and low lattice thermal conductivity, resulting in excellent overall thermoelectric performance. Furthermore, it has relatively pure phase and high density, making it a common mid-temperature thermoelectric material. 2. This invention introduces Co as magnetic nanoparticles into an N-type Mg3Sb2 thermoelectric matrix to form a magnetic nanocomposite thermoelectric material. The Seebeck coefficient of the composite thermoelectric material is significantly improved by utilizing the ferromagnetic magnon drag effect of the nanoparticles, thereby enhancing its electrical performance. Furthermore, the precipitated second phase and the magnetic properties after composite formation act as scattering centers, reducing the lattice thermal conductivity. Ultimately, the thermoelectric figure of merit at 723 K is approximately 28% higher than that of the substrate. N-type Mg3Sb2, as a mid-temperature thermoelectric material, has high potential for waste heat recovery. 3. This invention employs vacuum solid-state sintering combined with rapid hot pressing and Mg atmosphere annealing. Compared with the traditional high-energy ball milling process, it also achieves the preparation of N-type Mg3Sb2-based thermoelectric materials, but avoids the disadvantages of ball milling process such as easy sample adhesion and low yield. It also has the advantages of simpler and more efficient preparation process, and is convenient for large-scale synthesis. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0016] Figure 1 This is a process flow diagram of the present invention; Figure 2 The XRD patterns of the thermoelectric materials prepared in Examples 1-4 and Comparative Example 1 are shown. Figure 3 The graph shows the electrical conductivity of the thermoelectric materials prepared in Examples 1-4 and Comparative Example 1 as a function of temperature. Figure 4 The graph shows the Seebeck coefficient as a function of temperature for the thermoelectric materials prepared in Examples 1-4 and Comparative Example 1. Figure 5 The graph shows the power factor of the thermoelectric materials prepared in Examples 1-4 and Comparative Example 1 as a function of temperature. Figure 6 The graph shows the total thermal conductivity of the thermoelectric materials prepared in Examples 1-4 and Comparative Example 1 as a function of temperature. Figure 7 The graph shows the lattice thermal conductivity of the thermoelectric materials prepared in Examples 1-4 and Comparative Example 1 as a function of temperature. Figure 8 The thermoelectric figure of merit of the thermoelectric materials prepared in Examples 1-4 and Comparative Example 1 is plotted as a function of temperature. Figure 9 For Example 4, field emission scanning electron microscope (FESEM) images and energy dispersive spectroscopy (EDS) images of the sample surface were obtained. Figure 10 The high-magnification transmission electron microscope (HRTEM) image and inverse fast Fourier transform (IFFT) image of the sample obtained in Example 4 are shown. Detailed Implementation

[0017] To enable those skilled in the art to better understand the technical solutions of the present invention, the specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0018] In a first aspect, the present invention provides a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range, wherein the N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material can be denoted as xCo / Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01This also indicates that the n-type Mg3Sb2-based magnetic nanocomposite thermoelectric material is composed of Co magnetic nanoparticles and Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 It is composed of thermoelectric materials, where x is Co and Mg. 3.2 Sb 1.5 Bi 0.49 Te 0.01 The mass percentage, and the value of x ranges from 0.1% to 0.4%. In this invention, the values ​​of x are 0.1%, 0.2%, 0.3%, and 0.4%. Thus, by introducing ferromagnetic Co magnetic nanoparticles into an N-type Mg3Sb2 thermoelectric matrix to form a magnetic nanocomposite thermoelectric material, the Seebeck coefficient of the composite thermoelectric material is significantly improved by utilizing the magnetoresistive drag effect of the nanoparticles' ferromagnetism, thereby enhancing its electrical performance. Furthermore, the second phase precipitated after composite formation and the magnetic particles both act as scattering centers, scattering phonons and reducing the lattice thermal conductivity. Ultimately, the thermoelectric figure of merit at 723 K is approximately 28% higher than that of the substrate. N-type Mg3Sb2, as a mid-temperature thermoelectric material, has high potential for waste heat recovery.

[0019] Secondly, you can refer to Figure 1 As shown, this invention proposes a method for preparing high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric materials in the mid-temperature range. This method comprises four steps: Step 1: Mg can be processed 3.2 Sb 1.5 Bi 0.49 Te 0.01 Thermoelectric materials are weighed, proportioned, and sintered according to stoichiometry, and then Mg is added. 3.2 Sb 1.5 Bi 0.49 Te 0.01 Thermoelectric materials and Co nanoparticles are manually and mechanically mixed in an agate mortar until homogeneous, thereby obtaining magnetic nanocomposite powder. In this embodiment, Co nanoparticles and Mg... 3.2 Sb 1.5 Bi 0.49 Te 0.01 The mass percentage of thermoelectric materials is controlled within the range of 0.1% to 0.4%. Step 2: The obtained magnetic nanocomposite powder can be loaded into a graphite mold with an outer diameter of 50 mm and an inner diameter of 13 mm. The powder needs to be divided into two parts with a mass of 1.4 g and 1.15 g, and separated by carbon paper and carbon sheet during loading. Step 3: The assembled mold can be subjected to rapid hot pressing. The hot pressing procedure is as follows: sintering temperature is 873 K, sintering pressure is 80 MPa, and sintering time is 20 min. Step 4: The magnetic nanocomposite thermoelectric block obtained after rapid hot pressing can be cut and sanded to obtain elongated and arc-shaped blocky Mg3Sb2-based thermoelectric materials. These are placed in an alumina crucible and wrapped with Mg shavings, then sealed inside a quartz tube under vacuum. The quartz tube is then annealed in a muffle furnace. After annealing, N-type Mg3Sb2-based magnetic nanocomposite thermoelectric materials are obtained. In this embodiment, the annealing process is performed in a muffle furnace at 7 K min. -1 The temperature was increased to 873 K at a rate of [missing information], held for 1 h, and then increased at 7 K min [missing information]. -1 The rate at which it decreases to room temperature.

[0020] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0021] Compare with Example 1: An N-type Mg3Sb2-based thermoelectric material and its preparation method, wherein the chemical composition of the thermoelectric material is Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 The specific steps of the preparation method are as follows: Step 1: Mg can be processed 3.2 Sb 1.5 Bi 0.49 Te 0.01 According to the stoichiometric ratio of each element, Mg powder, Sb powder, Bi powder and Te powder are weighed as raw materials, and then mixed evenly in an agate mortar. Step 2: The obtained mixture powder can be cold-pressed into a block under a pressure of 585 MPa, then placed in an alumina crucible and vacuum-sealed in 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; Step 3: The product obtained from the reaction can be taken out of the quartz tube, ground into powder in an agate mortar, and then subjected to 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. 3.2 Sb 1.5 Bi 0.49 Te 0.01 Bulk thermoelectric materials; Step 4: The obtained product can be cut and sanded to obtain long strips and arc-shaped blocky Mg3Sb2-based thermoelectric materials. These are placed in an alumina crucible and wrapped with Mg shavings, then sealed in a quartz tube under vacuum. Annealing is then performed in a muffle furnace. After annealing, stable N-type Mg3Sb2-based magnetic nanocomposite thermoelectric materials are obtained. Regularly shaped, smooth-surfaced blocky Mg3Sb2-based thermoelectric materials are obtained, placed in an alumina crucible and wrapped with Mg shavings, then sealed in a quartz tube under a vacuum below 1.5 Pa. The quartz tube is then placed in a muffle furnace and heated to 8 K min. -1 The temperature was increased to 873 K at a rate of [missing information], held for 1 h, and then increased at 8 K min [missing information]. -1 The rate at which it decreases to room temperature.

[0022] The Mg prepared in this comparative example 3.2 Sb 1.5 Bi 0.49 Te 0.01 The XRD diffraction pattern of the thermoelectric material retains the Mg3Sb2 phase. Figure 2 Its conductivity at 303 ~ 773 K is 33521 ~ 42704 S m. -1 ( Figure 3 The Seebeck coefficient is -193 to -273 μV K. -1 ( Figure 4 The power factor is 10.7 ~ 13.2 μW cm⁻¹. -1 K -2 ( Figure 5 The total thermal conductivity is 1.13 ~ 0.81 W / m. -1 K -1 ( Figure 6 The lattice thermal conductivity is 0.96 ~ 0.63 W / m. -1 K -1 ( Figure 7 The zT value is 0.34 ~ 1.01 ( Figure 8 ). Example 1

[0023] A method for preparing a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range, wherein the chemical composition of the composite material is 0.1% Co / Mg. 3.2 Sb 1.5 Bi 0.49 Te 0.01 The specific steps of the preparation method are as follows: Step 1: Add Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01Thermoelectric materials and Co nanoparticles are mechanically ground in an agate mortar until homogeneous to obtain magnetic nanocomposite powder. In this embodiment, Co nanoparticles and Mg... 3.2 Sb 1.5 Bi 0.49 Te 0.01 The mass percentage of thermoelectric materials is controlled at 0.1%; Step 2: The obtained magnetic nanocomposite powder can be loaded into a graphite mold with an outer diameter of 50 mm and an inner diameter of 13 mm. The powder needs to be divided into two parts with a mass of 1.4 g and 1.15 g, and separated by carbon paper and carbon sheet during loading. Step 3: The assembled mold can be subjected to rapid hot pressing. The hot pressing procedure is as follows: sintering temperature 873 K, sintering pressure 80 MPa, and sintering time 20 min. Rapid hot pressing can suppress grain growth and achieve efficient densification. Rapid heating and short holding time can effectively limit excessive grain growth, which is beneficial to thermal properties. Applying pressure at high temperature can quickly eliminate internal porosity of the material to obtain a highly dense bulk, thereby ensuring good electrical transport properties. Step 4: The magnetic nanocomposite thermoelectric block obtained after rapid hot pressing can be cut and sanded to obtain elongated and arc-shaped blocky Mg3Sb2-based thermoelectric materials. These are placed in an alumina crucible and wrapped with Mg shavings, then sealed inside a quartz tube under vacuum. The quartz tube is then annealed in a muffle furnace. After annealing, N-type Mg3Sb2-based magnetic nanocomposite thermoelectric materials are obtained. In this embodiment, the annealing process is performed in a muffle furnace at 7 K min. -1 The temperature was increased to 873 K at a rate of [missing information], held for 1 h, and then increased at 7 K min [missing information]. -1 The rate at which it decreases to room temperature.

[0024] The 0.1% Co / Mg prepared in this example 3.2 Sb 1.5 Bi 0.49 Te 0.01 The XRD diffraction pattern of the thermoelectric material retains the Mg3Sb2 phase. Figure 2 Its conductivity at 303 ~ 773 K is 34439 ~ 15172 S m. -1 ( Figure 3 The Seebeck coefficient is -198 to -286 μV K. -1 ( Figure 4 The power factor is 12.4 ~ 16.1 μW cm⁻¹. -1 K -2 ( Figure 5 The total thermal conductivity is 1.08 ~ 0.8 W / m. -1 K -1 ( Figure 6 The lattice thermal conductivity is 0.92 ~ 0.62 W / m. -1 K -1 ( Figure 7 The zT value is 0.37 ~ 1.19 ( Figure 8 ). Example 2

[0025] A method for preparing a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range is disclosed. The specific steps of the preparation method are the same as those in Example 1, except that the chemical composition of the composite material is 0.2% Co / Mg. 3.2 Sb 1.5 Bi 0.49 Te 0.01 .

[0026] The 0.2% Co / Mg prepared in this example 3.2 Sb 1.5 Bi 0.49 Te 0.01 The XRD diffraction pattern of the thermoelectric material retains the Mg3Sb2 phase. Figure 2 Its conductivity at 303 ~ 773 K is 34413 ~ 14746 S m. -1 ( Figure 3 The Seebeck coefficient is -197 to -293 μV K. -1 ( Figure 4 The power factor is 12.6 ~ 16.6 μW / cm². -1 K -2 ( Figure 5 The total thermal conductivity is 1.06~0.82 W / m. -1 K -1 ( Figure 6 The lattice thermal conductivity is 0.89 ~ 0.64 W / m. -1 K -1 ( Figure 7 The zT value is 0.37 ~ 1.20 ( Figure 8 ). Example 3

[0027] A method for preparing a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range is disclosed. The specific steps of the preparation method are the same as in Example 1, except that the chemical composition of the composite material is 0.3% Co / Mg. 3.2 Sb 1.5 Bi 0.49 Te 0.01 .

[0028] The 0.3% Co / Mg prepared in this example3.2 Sb 1.5 Bi 0.49 Te 0.01 The XRD diffraction pattern of the thermoelectric material retains the Mg3Sb2 phase. Figure 2 Its conductivity at 303 ~ 773 K is 38704 ~ 14631 S m. -1 ( Figure 3 The Seebeck coefficient is -197 to -299 μV K. -1 ( Figure 4 The power factor is 13.1 ~ 17.6 μW / cm². -1 K -2 ( Figure 5 The total thermal conductivity is 1.08~0.80 W / m. -1 K -1 ( Figure 6 The lattice thermal conductivity is 0.89 ~ 0.62 W / m. -1 K -1 ( Figure 7 The zT value is 0.41 ~ 1.29 ( Figure 8 ). Example 4

[0029] A method for preparing a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range is disclosed. The specific steps of the preparation method are the same as those in Example 1, except that the chemical composition of the composite material is 0.4% Co / Mg. 3.2 Sb 1.5 Bi 0.49 Te 0.01 .

[0030] The 0.4% Co / Mg prepared in this example 3.2 Sb 1.5 Bi 0.49 Te 0.01 The XRD diffraction pattern of the thermoelectric material retains the Mg3Sb2 phase. Figure 2 Its conductivity at 303 ~ 773 K is 54193 ~ 20251 S m. -1 ( Figure 3 The Seebeck coefficient is -152 to -250 μV K. -1 ( Figure 4 The power factor is 12.6 ~ 17.4 μW / cm². -1 K -2 ( Figure 5 The total thermal conductivity is 1.08 ~ 0.78 W / m². -1 K -1 ( Figure 6The lattice thermal conductivity is 0.80 ~ 0.54 W / m. -1 K -1 ( Figure 7 The zT value is 0.35 ~ 1.28 ( Figure 8 ).

[0031] Field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS) images show Co magnetic nanoparticles in Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 Secondary phases precipitate on the surface of the matrix ( Figure 9 High-magnification TEM images show that the substrate can generate some dislocations due to the addition of appropriate amounts of Co magnetic nanoparticles. Figure 10 These dislocations are also phonon scattering centers, which reduce the thermal conductivity of the sample.

[0032] In summary, this invention, by varying the mass percentage of composite magnetic nanoparticles, yielded a magnetic nanocomposite thermoelectric material with a significantly improved zT (zt value) compared to the substrate within the temperature range of 300–723 K. An appropriate amount of ferromagnetic nanoparticles significantly enhanced the Seebeck coefficient of the composite thermoelectric material through the magnon drag effect, thereby improving its electrical performance. Furthermore, the precipitated second phase and magnetic particles after composite formation acted as scattering centers, reducing the lattice thermal conductivity. Ultimately, the composite sample with x=0.3% exhibited a thermoelectric figure of merit of approximately 28% higher than the substrate at 723 K.

[0033] Specifically, by optimizing the amount of ferromagnetic nanoparticles added, a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material (0.3% Co / Mg) in the mid-temperature range was prepared. 3.2 Sb 1.5 Bi 0.49 Te 0.01 This magnetic thermoelectric material has the following advantages: I. The magnetic resonator drag effect significantly improves the Seebeck coefficient of composite thermoelectric materials, thereby enhancing their electrical performance; Second, the precipitated second phase and the magnetic properties both act as scattering centers, scattering phonons and reducing the lattice thermal conductivity. Third, the thermoelectric figure of merit of the composite sample with x=0.3% was improved by approximately 28% at 723 K compared to the substrate. This provides more possibilities for thermoelectric devices for mid-temperature waste heat recovery.

[0034] 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. A method for preparing a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range, comprising the following steps: (1) Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 Thermoelectric materials and nano-Co magnetic particles are mechanically ground uniformly in a mortar to obtain magnetic nanocomposite powder; (2) Load the powder that has been ground evenly in step (1) into a graphite mold; (3) The mold assembled in step (2) is sintered under vacuum using a rapid hot pressing method to obtain Mg3Sb2-based magnetic nanocomposite thermoelectric material. (4) The product obtained in step (3) is cut and polished with sandpaper to obtain long strips and arc-shaped blocky Mg3Sb2-based thermoelectric materials. These are placed in an alumina crucible and wrapped with Mg shavings, then sealed in a quartz tube under vacuum. Annealing is performed in a muffle furnace. After annealing, stable N-type Mg3Sb2-based magnetic nanocomposite thermoelectric materials are obtained.

2. The method for preparing a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range according to claim 1, characterized in that, The nano-Co magnetic particles and Mg described in (1) 3.2 Sb 1.5 Bi 0.49 Te 0.01 The mass percentage of thermoelectric materials is 0.1% to 0.4%, and the mechanical grinding time is 10 min.

3. The method for preparing a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range according to claim 1, characterized in that, (2) The graphite mold to be loaded has an outer diameter of 50 mm and an inner diameter of 13 mm. The powder needs to be divided into two parts with a mass of 1.4 g and 1.15 g, and carbon paper and carbon sheet are used to separate them during loading.

4. The method for preparing a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range according to claim 1, characterized in that, The sintering temperature described in (3) is 873 K, the sintering pressure is 80 MPa, and the sintering time is 20 min.

5. The method for preparing a high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range according to claim 1, characterized in that, (4) The quartz tube has an outer diameter of 20 mm and an inner diameter of 17 mm. The annealing process is carried out in a muffle furnace at 7 K min. -1 The temperature was increased to 873 K at a rate of [missing information], held for 1 h, and then increased at 7 K min [missing information]. -1 The rate at which it decreases to room temperature.

6. A high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range, characterized in that, The N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material is obtained by the preparation method of the N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material as described in claims 1-5.

7. The high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range according to claim 6, characterized in that, The N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material consists of Co magnetic nanoparticles and Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 Thermoelectric materials are composites, and the N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material is denoted as xCo / Mg. 3.2 Sb 1.5 Bi 0.49 Te 0.01 Where x represents Co and Mg 3.2 Sb 1.5 Bi 0.49 Te 0.01 The mass percentage, and the value of x is in the range of 0.1% ≤ x ≤ 0.4%.

8. The high-performance N-type Mg3Sb2-based magnetic nanocomposite thermoelectric material in the mid-temperature range according to claim 7, characterized in that, The value of x is 0.3%.

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