A Yb / Cd co-doped p-type Mg 3 Sb 2 Thermoelectric materials and their preparation methods

Abstract

This invention discloses a Yb / Cd co-doped p-type Mg 3 Sb 2 Thermoelectric materials and their preparation methods belong to the field of energy conversion technology. A high-temperature vacuum solid-state reaction combined with rapid hot-pressing sintering process is employed, carried out in an argon atmosphere glove box according to the Mg... 3‑3x Cd 2x Yb x Sb 2 Mg, Cd, Yb, and Sb powders were weighed according to a stoichiometric ratio of 0 < x ≤ 0.4 and ground and mixed evenly. The mixed powder was cold-pressed into blocks, then placed in an alumina crucible and vacuum-sealed in a quartz tube. The mixture was then subjected to high-temperature solid-state sintering in a pit furnace, followed by cooling and grinding to obtain Mg. 3‑3x Cd 2x Yb x Sb 2 Powder thermoelectric materials. Finally, the powder material is vacuum hot-pressed and sintered under suitable pressure and temperature to obtain Mg. 3‑3x Cd 2x Yb x Sb 2 Bulk thermoelectric materials. The thermoelectric materials prepared by this invention have extremely low thermal conductivity while also possessing a high power factor, thus achieving excellent thermoelectric figure of merit and demonstrating great application potential in the field of energy conversion.

Description

A Yb / Cd co-doped p-type Mg3Sb2 thermoelectric material and its preparation method Technical Field

[0001] This invention belongs to the field of energy conversion technology, specifically relating to a Yb / Cd co-doped p-type Mg3Sb2 thermoelectric material and its preparation method. Background Technology

[0002] Thermoelectric energy conversion technology can continuously generate electricity using ubiquitous minute environmental temperature differences and can also rapidly and precisely cool micro-regions. Thermoelectric devices can convert (waste) heat into electrical energy by interweaving a certain number of p-type and n-type bulk thermoelectric material modules in series electrically and in parallel thermally, and vice versa. The conversion efficiency of thermoelectric devices mainly depends on the dimensionless thermoelectric figure of merit ZT, defined as ZT = S 2 σT / κ, where σ and S are the conductivity and Seebeck coefficient, respectively. 2 σ, also known as the power factor (PF), reflects electrical transport characteristics. κ is thermal conductivity, mainly composed of electronic thermal conductivity and lattice thermal conductivity, reflecting heat transport characteristics. T is the thermodynamic temperature in the Kelvin function. A high ZT value implies higher energy conversion efficiency and potentially higher output power, which is a core objective of thermoelectric research.

[0003] Mg3Sb2-based thermoelectric materials are typical Zintl phase compounds. Among them, n-type Mg3Sb2-based thermoelectric materials exhibit excellent thermoelectric properties and have become a research hotspot in recent years. Meanwhile, due to their low valley degeneracy, p-type Mg3Sb2-based thermoelectric materials have significantly lower thermoelectric performance than their corresponding n-type counterparts. Their intrinsically low electrical conductivity results in poor ZT performance. Therefore, current research on p-type Mg3Sb2-based thermoelectric materials mainly focuses on the modulation of electrical properties, improving conductivity through doping and other methods to enhance the thermoelectric ZT value. These strategies have achieved some optimization effects, but the increased electronic thermal conductivity resulting from higher electrical conductivity leads to a corresponding increase in the overall thermal conductivity of the material, thus greatly limiting the improvement of the ZT value. Therefore, finding high-performance p-type Mg3Sb2-based thermoelectric materials that can maintain low thermal conductivity while improving electrical conductivity is of great significance. Summary of the Invention

[0004] To address the aforementioned needs, the present invention aims to provide a Yb / Cd co-doped p-type Mg3Sb2 thermoelectric material and its preparation method. This method features a simple preparation process, inexpensive raw materials, good reproducibility, and ease of large-scale synthesis. The thermoelectric material obtained by this invention exhibits extremely low thermal conductivity and high electrical conductivity and Seebeck coefficient, demonstrating excellent thermoelectric performance and representing a potential commercial thermoelectric conversion material.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] A Yb / Cd co-doped p-type Mg3Sb2 thermoelectric material with the general chemical formula Mg 3-3x Cd 2x Yb x Sb2 (0 < x ≤ 0.4). Preferably, the Yb / Cd co-doped p-type Mg3Sb2 thermoelectric material is specifically Mg 2.7 Cd 0.2 Yb 0.1 Sb2, Mg 2.4 Cd 0.4 Yb 0.2 Sb2, Mg 2.1 Cd 0.6 Yb 0.3 Sb2, Mg 1.8 Cd 0.8 Yb 0.4 Sb2.

[0007] Furthermore, the above-mentioned Yb / Cd co-doped p-type Mg3Sb2-based thermoelectric material is prepared by using Mg, Cd, Yb, and Sb powders as raw materials, mixing them uniformly, and then using high-temperature vacuum solid-state reaction combined with rapid hot-pressing sintering to prepare Mg with good crystallinity and phase purity. 3-3x Cd 2x Yb x Sb2 bulk thermoelectric material. All raw materials need to be weighed and mixed under argon atmosphere protection. The specific steps of the preparation method are as follows:

[0008] Step 1: In an argon atmosphere glove box with water and oxygen content below 1 ppm, according to Mg... 3-3x Cd 2x Yb x To determine the stoichiometric ratio of Sb2, weigh out Mg powder, Cd powder, Yb powder, and Sb powder, and mix the powders thoroughly in an agate mortar.

[0009] Step 2: The obtained mixed powder is cold-pressed into blocks, then placed in an alumina crucible and vacuum-sealed inside a quartz tube. The quartz tube has a diameter of 15 mm and a wall thickness of 1.5 mm. During the vacuuming process, the vacuum level of the quartz tube is maintained below 1 Pa. The quartz tube is then placed in a pit furnace for a high-temperature solid-state sintering reaction. The solid-state sintering reaction conditions are: heating to 973 K at a rate of 1 K / min, holding at that temperature for 120 h, and then cooling to room temperature at a rate of 1 K / min.

[0010] Step 3: Remove the product obtained from the reaction from the quartz tube and grind it into powder in an agate mortar under an argon atmosphere to obtain Mg. 3-3x Cd 2x Yb x Sb2 powder thermoelectric materials;

[0011] Step 4: The obtained Mg 3-3x Cd 2x Yb x Sb2 powder was loaded into a graphite mold, sealed at the top and bottom with carbon rods, and wrapped with carbon paper. The mold was then hot-pressed and sintered for 20 min under an axial pressure of 80 MPa, a sintering temperature of 873 K, and a vacuum environment below 6 Pa to obtain high-density Mg. 3-3x Cd 2x Yb x Sb2 bulk thermoelectric material.

[0012] Based on the above technical solution, the beneficial effects of the present invention are as follows:

[0013] 1. This invention uses Mg, Cd, Yb, and Sb powders as raw materials and employs a high-temperature vacuum solid-state reaction combined with a rapid hot-pressing sintering process to produce high-performance Mg. 3-3x Cd 2x Yb x Sb2 bulk thermoelectric materials are characterized by high purity, simple processing, and ease of large-scale synthesis.

[0014] 2. The Mg prepared by this invention 3-3x Cd 2x Yb x The Sb2 bulk thermoelectric material has a pure phase and high density. As shown in Figures 1 and 2: Figure 1 shows the XRD patterns of five thermoelectric materials prepared in specific embodiments and comparative examples of this invention, all maintaining the Mg3Sb2 phase. Figure 2 shows Example 4, i.e., Mg... 1.8 Cd 0.8 Yb 0.4 The fracture surface SEM image of the Sb2 bulk thermoelectric material shows that the prepared bulk sample is compact and non-porous, exhibiting high density.

[0015] 3. The Yb / Cd co-doped p-type Mg prepared by this invention 3-3x Cd 2x Yb x Sb2 series thermoelectric materials exhibit excellent thermoelectric figures of merit due to the enhanced phonon scattering resulting from the doping of heavy atoms Yb and Cd, which significantly reduces thermal conductivity. Furthermore, Yb and Cd doping effectively improves the electrical conductivity of the samples while maintaining a high Seebeck coefficient, thereby increasing the power factor. 3-3x Cd 2x Yb xThe thermoelectric properties of the Sb2 series thermoelectric materials are shown in Figures 3-7. Figure 3 shows the thermal conductivity of the thermoelectric material as a function of temperature; Figure 4 shows the electrical conductivity as a function of temperature; Figure 5 shows the Seebeck coefficient as a function of temperature; Figure 6 shows the power factor as a function of temperature; and Figure 7 shows the thermoelectric figure of merit as a function of temperature. Figure 3 shows that the lowest thermal conductivity of the thermoelectric material is 0.51 W / m K, which is 27% lower than that of the control example, undoped Mg3Sb2 (0.70 W / m K). Figure 6 shows that the highest power factor of the thermoelectric material is 5.4 μW / m K. 2 Compared to the control example of undoped Mg3Sb2 (2.75 μW / mK), 2 The thermoelectric figure of merit was increased by 1.96 times; as can be seen from Figure 7, the highest thermoelectric figure of merit of the thermoelectric material was 0.78, which was 2.6 times higher than that of the control example undoped Mg3Sb2 (0.3). Attached Figure Description

[0016] Figure 1 shows the X-ray diffraction (XRD) patterns of Embodiments 1, 2, 3, 4, and the comparative example of the present invention.

[0017] Figure 2 is a high-resolution scanning electron microscope (SEM) image of the fracture surface in Embodiment 4 of the present invention.

[0018] Figure 3 shows the thermal conductivity (κ) data of Examples 1, 2, 3, 4 and the control example of the present invention at different temperatures.

[0019] Figure 4 shows the conductivity (σ) data of Examples 1, 2, 3, 4 and the control example of the present invention at different temperatures.

[0020] Figure 5 shows the Seebeck coefficient (S) of Examples 1, 2, 3, 4 and the control example of the present invention at different temperatures.

[0021] Figure 6 shows the power factor (PF) data of Embodiments 1, 2, 3, 4 and the control example of the present invention at different temperatures.

[0022] Figure 7 shows the thermoelectric figure of merit (ZT) data of Embodiments 1, 2, 3, 4 and the control example of the present invention at different temperatures. Detailed Implementation

[0023] To further understand the present invention, the following detailed description of the embodiments and accompanying drawings is provided in conjunction with the examples and figures, but these should not be construed as limiting the scope of protection of the present invention. Example 1

[0024] A Yb / Cd co-doped p-type Mg3Sb2 thermoelectric material and its preparation method. The chemical formula of the thermoelectric material is Mg3Sb2. 2.7 Cd 0.2 Yb 0.1 The specific steps of the preparation method for Sb2 are as follows:

[0025] Step 1: In an argon atmosphere glove box with water and oxygen content below 1 ppm, according to Mg... 2.7 Cd 0.2 Yb 0.1 To determine the stoichiometric ratio of Sb2, weigh out Mg powder, Cd powder, Yb powder, and Sb powder, and mix the powders thoroughly in an agate mortar.

[0026] Step 2: The obtained mixed powder is cold-pressed into blocks, then placed in an alumina crucible and vacuum-sealed inside a quartz tube. The quartz tube has a diameter of 15 mm and a wall thickness of 1.5 mm. During the vacuuming process, the vacuum level of the quartz tube is maintained below 1 Pa. The quartz tube is then placed in a pit furnace for a high-temperature solid-state sintering reaction. The solid-state sintering reaction conditions are: heating to 973 K at a rate of 1 K / min, holding at that temperature for 120 h, and then cooling to room temperature at a rate of 1 K / min.

[0027] Step 3: Remove the product obtained from the reaction from the quartz tube and grind it into powder in an agate mortar under an argon atmosphere to obtain Mg. 2.7 Cd 0.2 Yb 0.1 Sb2 powder thermoelectric materials;

[0028] Step 4: The obtained Mg 2.7 Cd 0.2 Yb 0.1 Sb2 powder was loaded into a graphite mold, sealed at the top and bottom with carbon rods, and wrapped with carbon paper. The mold was then hot-pressed and sintered for 20 min under an axial pressure of 80 MPa, a sintering temperature of 873 K, and a vacuum environment below 6 Pa to obtain high-density Mg. 2.7 Cd 0.2 Yb 0.1 Sb2 bulk thermoelectric material.

[0029] Characterization revealed that the Yb / Cd co-doped Mg prepared in this embodiment... 2.7 Cd 0.2 Yb 0.1 The Sb2 thermoelectric material retains the Mg3Sb2 phase (Figure 1). Its thermal conductivity ranges from 0.81 W / m K to 0.58 W / m K in the range of 323 K to 773 K (Figure 3); its electrical conductivity ranges from 3250 S / m to 4800 S / m (Figure 4); its Seebeck coefficient ranges from 216 μV / K to 303 μV / K (Figure 5); and its power factor is 1.9 μW / m K.2 ~3.35 μW / m K 2 (Figure 6); the final ZT value was 0.078–0.44 (Figure 7). Compared with the control example of undoped Mg3Sb2, the thermal conductivity of this example decreased significantly, reaching 0.58 W / m K at 773 K, a 17% reduction compared to the control example (0.7 W / m K); the electrical conductivity increased slightly, the Seebeck coefficient decreased slightly, and the power factor increased slightly, reaching a maximum value of 3.35 μW / m K. 2 Compared to the control example (2.75 μW / mK) 2 The ZT value was increased by 1.2 times. The final ZT value reached a maximum of 0.44, which was 1.46 times higher than the control example (0.3). Example 2

[0030] A Yb / Cd co-doped p-type Mg3Sb2 thermoelectric material and its preparation method. The chemical formula of the thermoelectric material is Mg3Sb2. 2.4 Cd 0.4 Yb 0.2 The specific steps of the preparation method for Sb2 are as follows:

[0031] Step 1: In an argon atmosphere glove box with water and oxygen content below 1 ppm, according to Mg... 2.4 Cd 0.4 Yb 0.2 To determine the stoichiometric ratio of Sb2, weigh out Mg powder, Cd powder, Yb powder, and Sb powder, and mix the powders thoroughly in an agate mortar.

[0032] Step 2: The obtained mixed powder is cold-pressed into blocks, then placed in an alumina crucible and vacuum-sealed inside a quartz tube. The quartz tube has a diameter of 15 mm and a wall thickness of 1.5 mm. During the vacuuming process, the vacuum level of the quartz tube is maintained below 1 Pa. The quartz tube is then placed in a pit furnace for a high-temperature solid-state sintering reaction. The solid-state sintering reaction conditions are: heating to 973 K at a rate of 1 K / min, holding at that temperature for 120 h, and then cooling to room temperature at a rate of 1 K / min.

[0033] Step 3: Remove the product obtained from the reaction from the quartz tube and grind it into powder in an agate mortar under an argon atmosphere to obtain Mg. 2.4 Cd 0.4 Yb 0.2 Sb2 powder thermoelectric materials;

[0034] Step 4: The obtained Mg 2.4 Cd 0.4 Yb 0.2Sb2 powder was loaded into a graphite mold, sealed at the top and bottom with carbon rods, and wrapped with carbon paper. The mold was then hot-pressed and sintered for 20 min under an axial pressure of 80 MPa, a sintering temperature of 873 K, and a vacuum environment below 6 Pa to obtain high-density Mg. 2.4 Cd 0.4 Yb 0.2 Sb2 bulk thermoelectric material.

[0035] Characterization revealed that the Yb / Cd co-doped Mg prepared in this embodiment... 2.4 Cd 0.4 Yb 0.2 The Sb2 thermoelectric material retains the Mg3Sb2 phase (Figure 1). Its thermal conductivity ranges from 0.71 W / m K to 0.55 W / m K in the range of 323 K to 773 K (Figure 3); its electrical conductivity ranges from 4500 S / m to 7600 S / m (Figure 4); its Seebeck coefficient ranges from 190 μV / K to 295 μV / K (Figure 5); and its power factor is 2.7 μW / m K. 2 ~4.0 μW / m K 2 (Figure 6); the final ZT value was 0.12–0.57 (Figure 7). Compared with the control example of undoped Mg3Sb2, the thermal conductivity of this example decreased significantly, reaching 0.55 W / m K at 773 K, a 21% reduction compared to the control example (0.7 W / m K); the electrical conductivity increased slightly, the Seebeck coefficient decreased slightly, and the power factor increased slightly, reaching a maximum value of 4.0 μW / m K. 2 Compared to the control example (2.75 μW / mK) 2 The ZT value was increased by 1.45 times. The final ZT value reached a maximum of 0.57, which was 1.9 times higher than the control example (0.3). Example 3

[0036] A Yb / Cd co-doped p-type Mg3Sb2 thermoelectric material and its preparation method. The chemical formula of the thermoelectric material is Mg3Sb2. 2.1 Cd 0.6 Yb 0.3 The specific steps of the preparation method for Sb2 are as follows:

[0037] Step 1: In an argon atmosphere glove box with water and oxygen content below 1 ppm, according to Mg... 2.1 Cd 0.6 Yb 0.3 To determine the stoichiometric ratio of Sb2, weigh out Mg powder, Cd powder, Yb powder, and Sb powder, and mix the powders thoroughly in an agate mortar.

[0038] Step 2: The obtained mixed powder is cold-pressed into blocks, then placed in an alumina crucible and vacuum-sealed inside a quartz tube. The quartz tube has a diameter of 15 mm and a wall thickness of 1.5 mm. During the vacuuming process, the vacuum level of the quartz tube is maintained below 1 Pa. The quartz tube is then placed in a pit furnace for a high-temperature solid-state sintering reaction. The solid-state sintering reaction conditions are: heating to 973 K at a rate of 1 K / min, holding at that temperature for 120 h, and then cooling to room temperature at a rate of 1 K / min.

[0039] Step 3: Remove the product obtained from the reaction from the quartz tube and grind it into powder in an agate mortar under an argon atmosphere to obtain Mg. 2.1 Cd 0.6 Yb 0.3 Sb2 powder thermoelectric materials;

[0040] Step 4: The obtained Mg 2.1 Cd 0.6 Yb 0.3 Sb2 powder was loaded into a graphite mold, sealed at the top and bottom with carbon rods, and wrapped with carbon paper. The mold was then hot-pressed and sintered for 20 min under an axial pressure of 80 MPa, a sintering temperature of 873 K, and a vacuum environment below 6 Pa to obtain high-density Mg. 2.1 Cd 0.6 Yb 0.3 Sb2 bulk thermoelectric material.

[0041] Characterization revealed that the Yb / Cd co-doped Mg prepared in this embodiment... 2.1 Cd 0.6 Yb 0.3 The Sb2 thermoelectric material retains the Mg3Sb2 phase (Figure 1). Its thermal conductivity ranges from 0.70 W / m K to 0.53 W / m K in the range of 323 K to 773 K (Figure 3); its electrical conductivity ranges from 5700 S / m to 10500 S / m (Figure 4); its Seebeck coefficient ranges from 182 μV / K to 281 μV / K (Figure 5); and its power factor is 3.5 μW / m K. 2 ~4.8 μW / m K 2 (Figure 6); the final ZT values ​​were 0.16–0.69 (Figure 7). Compared with the control example of undoped Mg3Sb2, the thermal conductivity of this example decreased significantly, reaching 0.53 W / m K at 773 K, a 24% reduction compared to the control example (0.7 W / m K); the electrical conductivity increased slightly, the Seebeck coefficient decreased slightly, and the power factor increased slightly, reaching a maximum value of 4.8 μW / m K. 2 Compared to the control example (2.75 μW / mK) 2The ZT value was increased by 1.75 times. The final ZT value reached a maximum of 0.69, which was 2.3 times higher than the control example (0.3). Example 4

[0042] A Yb / Cd co-doped p-type Mg3Sb2 thermoelectric material and its preparation method. The chemical formula of the thermoelectric material is Mg3Sb2. 1.8 Cd 0.8 Yb 0.4 The specific steps of the preparation method for Sb2 are as follows:

[0043] Step 1: In an argon atmosphere glove box with water and oxygen content below 1 ppm, according to Mg... 1.8 Cd 0.8 Yb 0.4 To determine the stoichiometric ratio of Sb2, weigh out Mg powder, Cd powder, Yb powder, and Sb powder, and mix the powders thoroughly in an agate mortar.

[0044] Step 2: The obtained mixed powder is cold-pressed into blocks, then placed in an alumina crucible and vacuum-sealed inside a quartz tube. The quartz tube has a diameter of 15 mm and a wall thickness of 1.5 mm. During the vacuuming process, the vacuum level of the quartz tube is maintained below 1 Pa. The quartz tube is then placed in a pit furnace for a high-temperature solid-state sintering reaction. The solid-state sintering reaction conditions are: heating to 973 K at a rate of 1 K / min, holding at that temperature for 120 h, and then cooling to room temperature at a rate of 1 K / min.

[0045] Step 3: Remove the product obtained from the reaction from the quartz tube and grind it into powder in an agate mortar under an argon atmosphere to obtain Mg. 1.8 Cd 0.8 Yb 0.4 Sb2 powder thermoelectric materials;

[0046] Step 4: The obtained Mg 1.8 Cd 0.8 Yb 0.4 Sb2 powder was loaded into a graphite mold, sealed at the top and bottom with carbon rods, and wrapped with carbon paper. The mold was then hot-pressed and sintered for 20 min under an axial pressure of 80 MPa, a sintering temperature of 873 K, and a vacuum environment below 6 Pa to obtain high-density Mg. 1.8 Cd 0.8 Yb 0.4 Sb2 bulk thermoelectric material.

[0047] Characterization revealed that the Yb / Cd co-doped Mg prepared in this embodiment... 1.8 Cd 0.8 Yb 0.4The Sb2 thermoelectric material retains the Mg3Sb2 phase (Figure 1). Its thermal conductivity ranges from 0.67 W / m K to 0.51 W / m K in the range of 323 K to 773 K (Figure 3); its electrical conductivity ranges from 6900 S / m to 14000 S / m (Figure 4); its Seebeck coefficient ranges from 177 μV / K to 276 μV / K (Figure 5); and its power factor is 4.4 μW / m K. 2 ~5.4 μW / m K 2 (Figure 6); the final ZT values ​​were 0.21–0.78 (Figure 7). Compared with the control example of undoped Mg3Sb2, the thermal conductivity of this example decreased significantly, reaching 0.51 W / m K at 773 K, a 27% reduction compared to the control example (0.7 W / m K); the electrical conductivity increased slightly, the Seebeck coefficient decreased slightly, and the power factor increased slightly, reaching a maximum value of 5.4 μW / m K. 2 Compared to the control example (2.75 μW / mK) 2 The ZT value increased by 1.96 times. The final ZT value reached a maximum of 0.78, which was 2.6 times higher than the control example (0.3).

[0048] Comparison Example

[0049] This invention also relates to the preparation of a thermoelectric material made from a pure, undoped Mg3Sb2 sample, as a comparative example. The chemical formula of the thermoelectric material is Mg3Sb2, and the preparation method comprises the following steps:

[0050] Step 1: Weigh Mg powder and Sb powder according to the stoichiometric ratio of Mg3Sb2 in an argon atmosphere glove box with water and oxygen content below 1 ppm, and mix the powders evenly in an agate mortar.

[0051] Step 2: The obtained mixed powder is cold-pressed into blocks, then placed in an alumina crucible and vacuum-sealed inside a quartz tube. The quartz tube has a diameter of 15 mm and a wall thickness of 1.5 mm. During the vacuuming process, the vacuum level of the quartz tube is maintained below 1 Pa. The quartz tube is then placed in a pit furnace for a high-temperature solid-state sintering reaction. The solid-state sintering reaction conditions are: heating to 973 K at a rate of 1 K / min, holding at that temperature for 120 h, and then cooling to room temperature at a rate of 1 K / min.

[0052] Step 3: Remove the product obtained from the reaction from the quartz tube and grind it into powder in an agate mortar under argon atmosphere protection to obtain Mg3Sb2 powder thermoelectric material.

[0053] Step 4: The obtained Mg3Sb2 powder is loaded into a graphite mold, sealed at the top and bottom with carbon rods and wrapped with carbon paper. It is then hot-pressed and sintered for 20 min under an axial pressure of 80 MPa, a sintering temperature of 873 K and a vacuum environment of less than 6 Pa to obtain a high-density Mg3Sb2 bulk thermoelectric material.

[0054] Characterization showed that the XRD diffraction pattern of the Mg3Sb2 thermoelectric material prepared in this comparative example conformed to the Mg3Sb2 phase (Figure 1). Its thermal conductivity ranged from 1.44 W / m K to 0.7 W / m K (Figure 3) in the range of 323 K to 773 K; its electrical conductivity ranged from 272 S / m to 2423 S / m (Figure 4); its Seebeck coefficient ranged from 337 μV / K to 408 μV / K (Figure 5); and its power factor was 0.35 μW / m K. 2 ~2.75 μW / m K 2 (See Figure 6); The final ZT value is 0.0087 to 0.30 (See Figure 7).

Claims

1. A Yb / Cd co-doped p-type Mg3Sb2 thermoelectric material and its preparation method, characterized in that... It includes the following steps: (1) According to Mg 3-3x Cd 2x Yb x The stoichiometric ratio of Sb2 (0 < x ≤ 0.4) is determined by weighing Mg powder, Cd powder, Yb powder and Sb powder in an argon atmosphere glove box with water and oxygen content below 1 ppm. The powders are then mixed evenly in an agate mortar. (2) The resulting mixture is cold-pressed into a block, then placed in an alumina crucible and vacuum-sealed in a quartz tube. The diameter of the quartz tube is 15 ~ 20 mm and the wall thickness is 1.5 ~ 2 mm. During the vacuuming process, the vacuum degree of the quartz tube is kept below 1 Pa. The quartz tube is placed in a pit furnace for high-temperature solid-state sintering reaction. The conditions for the solid-state sintering reaction are: heating to 873 ~ 1073 K at a rate of 1 ~ 5 K / min, holding for 72 ~ 144 h, and then cooling to room temperature at a rate of 1 ~ 5 K / min. (3) The product obtained in step (2) is taken out of the quartz tube and ground into powder in an agate mortar under argon atmosphere protection to obtain Mg. 3-3x Cd 2x Yb x Sb2 powder thermoelectric material; (4) the obtained Mg 3-3x Cd 2x Yb x Sb2 powder was loaded into a graphite mold, sealed at the top and bottom with carbon rods, and wrapped with carbon paper. The mold was then hot-pressed and sintered for 10–60 min under an axial pressure of 50–80 MPa, a sintering temperature of 823–923 K, and a vacuum environment below 6 Pa to obtain high-density Mg. 3-3x Cd 2x Yb x Sb2 bulk thermoelectric material.

2. The Yb / Cd co-doped p-type Mg3Sb2 thermoelectric material and its preparation method according to claim 1, characterized in that, The prepared Mg3Sb2-based thermoelectric material is p-type, and the thermal conductivity is significantly reduced due to the doping of heavy atoms Yb and Cd. Simultaneously, the doping of Yb and Cd can improve the power factor. Ultimately, through dual optimization of thermal and electrical properties, Yb / Cd co-doped Mg... 3-3x Cd 2x Yb x The thermoelectric figure of merit of the Sb2 thermoelectric material reached a maximum of 0.78 at 773 K, which is 2.6 times higher than that of the undoped Mg3Sb2 sample at the same temperature (0.3).

3. The Yb / Cd co-doped p-type Mg3Sb2 thermoelectric material and its preparation method according to claim 1, characterized in that, The general chemical formula of the Mg3Sb2-based thermoelectric material mentioned in step (1) is Mg 3-3x Cd 2x Yb x Sb2, where 0 < x ≤ 0.4; x = 0.4, that is, the p-type Mg3Sb2-based thermoelectric material is specifically Mg 1.8 Cd 0.8 Yb 0.4 Sb2.

4. The Yb / Cd co-doped p-type Mg3Sb2 thermoelectric material and its preparation method according to claim 1, characterized in that, In step (1), the argon atmosphere glove box with water and oxygen content below 1 ppm is prepared according to Mg 3-3x Cd 2x Yb x Sb2 is prepared by weighing and mixing Mg powder, Cd powder, Yb powder and Sb powder in stoichiometric ratio, and then cold-pressing it into a block before proceeding with the subsequent reaction.

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