N-type smmg2sb2-based thermoelectric material and preparation method thereof

Abstract

The application provides an n-type SmMg2Sb2-based thermoelectric material and a preparation method thereof, and the chemical general formula of the n-type SmMg2Sb2-based thermoelectric material is SmMg 2.3 Sb 2‑x‑y Bi y Te x , 0 < x < 0.03, 0 < y < 0.5. The SmMg2Sb2-based thermoelectric material of the technical scheme has a lower intrinsic hole concentration, and the hole concentration is about 4*10 16 cm ‑3 -3 cm-1 at room temperature. Meanwhile, the electron mobility is 220% higher than the hole mobility, the electron concentration and the hole concentration are relatively small at high temperature (>600 K), the material presents n-type conductive characteristics, and the state density effective mass is 2.6 m 0, which is higher than all reported p-type AB2X2 alloys.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials technology, and particularly relates to an n-type SmMg2Sb2-based thermoelectric material and its preparation method. Background Technology

[0002] The properties of thermoelectric materials are determined by the dimensionless figure of merit zT = [S 2 σ / (κ e +κ L Characterized by increasing electrical conductivity σ and Seebeck coefficient S, while simultaneously decreasing thermal conductivity κ (κ is the carrier thermal conductivity κ). e lattice thermal conductivity κ L and bipolar effect κ B The sum of these three physical quantities (zT, z-T, z-T) is key to material optimization, but these three physical quantities are interrelated and difficult to control individually, which is the main reason limiting the improvement of the thermoelectric performance of materials. An ideal thermoelectric material should have a high Seebeck coefficient, high electrical conductivity, and low lattice thermal conductivity to obtain a large zT value.

[0003] AB₂X₂ (1-2-2 type) Zintl phase compounds are polar intermetallic compounds that possess both ionic and covalent bonds in their crystals. Within the crystal, the covalently bonded anionic framework provides excellent pathways for electrical transport, while the complex crystal structure results in very low intrinsic lattice thermal conductivity. AB₂X₂ compounds have a very rich elemental composition. The A-site elements are generally alkaline earth elements or divalent rare earth elements (e.g., Mg, Ca, Ba, Sr, Yb, Eu, Sm). The B-site elements are mainly transition elements (e.g., Mn, Zn, Cd). The X-site elements include Sb and Bi. This rich diversity and unique crystal structure have attracted widespread attention in the thermoelectric field. Due to the significant intrinsic cation vacancies in AB₂X₂ alloys, most AB₂X₂ alloys exhibit strong p-type conductivity. Figure 1 The image shows the crystal structure of AB2X2. It can be seen that in AB2X2-type Zintl phase materials, vacancies readily form at the A-site. One A-site vacancy generates two holes, therefore AB2X2 materials generally exhibit intrinsic p-type conductivity. The self-compensating effect of cation vacancy defects makes it difficult to prepare n-type AB2X2 alloys. Meanwhile, Figure 2 The value represents the A-site vacancy formation energy in the AZn2Sb2 alloy (A: Yb, Ca, Eu, Sr). Literature calculations show that the defect formation energy of A-site vacancies decreases as the Fermi level shifts towards the conduction band. This means that during n-type doping, the reduced A-site vacancy formation energy leads to more vacancies being generated, increasing the hole concentration and making it difficult to obtain n-type AB2X2. Therefore, current reports mainly focus on the thermoelectric properties of p-type AB2X2, with very few reports on n-type AB2X2 alloys.

[0004] However, a complete thermoelectric device requires a material pair with matching thermoelectric properties and thermal stability. At the same time, theoretical calculations also show that the conduction band bottom of the AB2X2 alloy is located at a k-point with higher symmetry in the Brillouin zone, having better thermoelectric properties. Therefore, the research on the thermoelectric properties of n-type AB2X2 alloys has high value and significance. SUMMARY OF THE INVENTION

[0005] In view of the above technical problems, the present invention discloses an n-type SmMg2Sb2-based thermoelectric material and its preparation method. The intrinsic hole concentration of this material is about 4×10 16 cm -3 , and the electron mobility is 220% higher than the hole mobility. When the temperature is above 600K, the material exhibits n-type semiconductor characteristics.

[0006] For this, the technical solution adopted by the present invention is as follows:

[0007] An n-type SmMg2Sb2-based thermoelectric material, whose chemical general formula is SmMg 2.3 Sb 2-x-y Bi y Te x , where 0 < x ≤ 0.03 and 0 ≤ y ≤ 0.5. The SmMg2Sb2-based thermoelectric material adopting this technical solution exhibits n-type conductive characteristics when the temperature is above 600K, breaking through the limitation that the existing AB2X2 alloys are basically p-type, and the effective mass of the density of states is higher than that of all reported p-type AB2X2 alloys.

[0008] As a further improvement of the present invention, the chemical general formula of the n-type SmMg2Sb2-based thermoelectric material is SmMg 2.3 Sb2, SmMg 2.3 Sb 2-x Te x , or SmMg 2.3 Sb 1.97-y Bi y Te 0.03 , where 0 ≤ x ≤ 0.03 and 0 ≤ y ≤ 0.5.

[0009] As a further improvement of the present invention, x is 0, 0.0005, 0.010, 0.020, 0.025 or 0.030, and y is 0, 010, 0.25 or 0.5.

[0010] This invention also discloses a method for preparing the n-type SmMg2Sb2-based thermoelectric material as described above. In an argon atmosphere, Sm powder, Mg powder, Sb powder, Bi powder, and Te powder are weighed according to the stoichiometric ratio of the general chemical formula and placed into a ball mill jar for high-energy ball milling for 4-8 hours. The resulting alloy powder is then placed into a graphite mold and sintered at 900-1000℃ for 1.5-3 minutes at a temperature of 100℃ / min. The sintering pressure is 40-60 MPa, and the material is cooled in the furnace to obtain the n-type SmMg2Sb2-based thermoelectric material.

[0011] As a further improvement of the present invention, the sintering temperature is 950°C and the pressure is 50 MPa.

[0012] As a further improvement of the present invention, the ball milling time is 6 hours.

[0013] As a further improvement of the present invention, the ball-to-material ratio in the ball mill jar is 1:0.8 to 1.2.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] The technical solution of this invention utilizes a mechanical alloying method to prepare n-type SmMg2Sb2-based thermoelectric materials. The resulting SmMg2Sb2-based thermoelectric materials exhibit a low intrinsic hole concentration of approximately 4 × 10⁻⁶ at room temperature. 16 cm -3 Meanwhile, its electron mobility is 220% higher than its hole mobility. Due to intrinsic excitation, the difference between electron and hole concentrations is small at high temperatures (>600K), and the material exhibits n-type conductivity. By controlling the electron concentration through Mg excess and Te doping, n-type SmMg2Sb2-based thermoelectric materials can be obtained at room temperature. The band structure shows that the conduction band degeneracy of the SmMg2Sb2-based thermoelectric material is 6, and experimental results show that the effective mass of the n-type density of states is 2.6m0, which is higher than all reported p-type AB2X2 alloys. The excellent conduction band structure gives the n-type SmMg2Sb2-based thermoelectric material high electrical transport performance. Finally, after controlling the electron concentration and lattice thermal conductivity, the zT value of the n-type SmMg2Sb2-based thermoelectric material reaches 1.0 at 873K. The technical solution of this invention has important guiding significance for the study of the n-type thermoelectric properties of other promising AB2X2 alloys. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the vacancy defects in the AB2X2 alloy of the prior art of this invention.

[0017] Figure 2 It is the A-site vacancy formation energy in the AZn2Sb2 alloy (A: Yb, Ca, Eu, Sr) of the prior art of this invention.

[0018] Figure 3 This is SmMg from Example 1 of the present invention. 2.3 Comparison of thermoelectric properties of Sb2 and SmMg2Sb2 in Example 2; where (a) is a comparison of Seebeck coefficients and (b) is a comparison of Hall carrier concentrations.

[0019] Figure 4 This is SmMg from Example 1 of the present invention. 2.3 The performance curves of Sb2; where (a) is the absolute value of the Hall coefficient at varying temperatures, and (b) is the value of SmMg at temperatures above 600 K. 2.3 Calculated electron and hole mobility of Sb2 at varying temperatures.

[0020] Figure 5 This is SmMg from Example 3 of the present invention. 2.3 Sb 2-x Te x Thermoelectric performance diagrams for (x = 0.005, 0.010, 0.020, 0.025, 0.030); where (a) is the electron concentration, (b) is the Seebeck coefficient, (c) is the power factor, and (d) is the relationship between the Seebeck coefficient value and the Hall carrier concentration at 573 K (the curves are calculated by the single-band model).

[0021] Figure 6 This is a band structure diagram of SmMg2Sb2 according to Embodiment 2 of the present invention; wherein, (a) is the band structure of SmMg2Sb2, (b) is the n-type Fermi level, and (c) is the p-type Fermi level (the Fermi level is taken as 0.05 eV above the bottom of the conduction band and 0.05 eV below the top of the valence band).

[0022] Figure 7 This is the phonon dispersion relation diagram of SmMg2Sb2 in Embodiment 2 of the present invention.

[0023] Figure 8 This is SmMg from Example 4 of the present invention. 2.3 Sb 1.97-y Bi y Te 0.03 Variable-temperature lattice thermal conductivity curves (y = 0, 0.10, 0.25, 0.50).

[0024] Figure 9 This is SmMg from Example 4 of the present invention. 2.3 Sb 1.97-y Bi y Te 0.03 Analysis of zT values ​​for varying temperatures (y = 0, 0.10, 0.25, 0.50).

[0025] Figure 10This involves a temperature-varying zT analysis of the SmMg2Sb2-based thermoelectric material of this invention, and a comparison of the maximum zT values ​​of other n-type Zintl phase materials in the comparative example. Detailed Implementation

[0026] The preferred embodiments of the present invention will be described in further detail below.

[0027] Example 1

[0028] Pure elements are classified according to SmMg 2.3 To determine the atomic stoichiometry of Sb2, Sm powder, Mg powder, and Sb powder were weighed and placed in a ball mill jar for ball milling for 6 hours. The resulting alloy powder was then placed in a graphite mold and sintered for 2 minutes at a temperature of 950℃ and a pressure of 50MPa, followed by furnace cooling to obtain n-type SmMg. 2.3 Sb2 thermoelectric material.

[0029] Example 2

[0030] According to the atomic stoichiometry of SmMg2Sb2, Sm powder, Mg powder, and Sb powder were weighed and placed in a ball mill jar for ball milling for 6 hours. The resulting alloy powder was then placed in a graphite mold and sintered for 2 minutes at a temperature of 950℃ and a pressure of 50MPa, followed by furnace cooling to obtain n-type SmMg2Sb ... 2.3 Sb2 thermoelectric material.

[0031] The obtained SmMg2Sb2 is a typical AB2X2 alloy. The intrinsic hole concentration of SmMg2Sb2 at room temperature is approximately 4 × 10⁻⁶. 16 cm -3 It is at a lower level compared to other AB2X2 alloys disclosed in the prior art.

[0032] SmMg in Example 1 2.3 The temperature-dependent performance results of Sb2 and SmMg2Sb2 in Example 2 are as follows: Figure 3 As shown, the intrinsic hole concentration in SmMg2Sb2 is at a low level, approximately 4 × 10⁻⁶ at room temperature. 16 cm -3 Intrinsic SmMg2Sb2 transforms into an n-type semiconductor above 600K. Adding excess Mg suppresses the intrinsic hole concentration, leading to the transformation of SmMg2Sb2 into an n-type semiconductor. 2.3 Sb2 transforms into an n-type semiconductor at 450K.

[0033] SmMg 2.3 The absolute value of the variable-temperature Hall coefficient of Sb2 is as follows: Figure 4 As shown in (a), above 600K, SmMg 2.3The calculated electron and hole mobilities of Sb2 at varying temperatures are as follows: Figure 4 As shown in (b), compared to holes, SmMg 2.3 Sb2 has higher electron mobility, and when the electron concentration and hole concentration in the material are close, it easily exhibits n-type semiconductor characteristics.

[0034] The band structure diagram of SmMg2Sb2 is shown below. Figure 6 As shown, the conduction band degeneracy of SmMg2Sb2 is 6, and the valence band degeneracy is 1. Therefore, the effective mass of the n-type alloy is 2.6m0, which is higher than the effective mass of the p-type AB2X2 alloy. The phonon dispersion relation is shown in the figure. Figure 7 As shown, SmMg2Bi2 exhibits a lower phonon frequency compared to SmMg2Sb2. This is primarily because the mass of Bi atoms is higher than that of Sb atoms; therefore, introducing Bi atoms into SmMg2Sb2 can reduce the phonon frequency of the alloy and optimize the lattice thermal conductivity.

[0035] Example 3

[0036] Pure elements are classified according to SmMg 2.3 Sb 2-x Te x Using atomic stoichiometry (x = 0.005, 0.010, 0.020, 0.025, 0.030 respectively), Sm powder, Mg powder, Sb powder, and Te powder were weighed and placed in a ball mill jar for ball milling for 6 hours. The resulting alloy powder was then placed in a graphite mold and sintered for 2 minutes at a sintering temperature of 950℃ and a pressure of 50MPa, followed by furnace cooling to obtain n-type SmMg. 2.3 Sb 2-x Te x Thermoelectric materials.

[0037] The electron concentration, Seebeck coefficient, power factor, and the relationship between the Seebeck coefficient at 573 K and the Hall carrier concentration in this embodiment are as follows: Figure 5 As shown, the electron concentration of the alloy is significantly increased after incorporating Te atoms at the Sb sites. Specifically, SmMg 2.3 Sb 1.995 Te 0.005 The room temperature electron concentration is ~0.3×10⁻⁶. 20 cm -3 As the Te content increases, the electron concentration of the sample gradually increases. When x = 0.03, the room temperature electron concentration of the sample reaches ~0.7 × 10⁻⁶. 20 cm -3 SmMg at room temperature 2.3 Sb 1.995 Te 0.005 The Zebeck coefficient is approximately -260V K.-1 And SmMg 2.3 Sb 1.97 Te 0.03 The Seebeck coefficient at room temperature is approximately -195V K. -1 The SmMg at room temperature was calculated using a single-band model. 2.3 Sb 2-x Te x The effective mass of the alloy (x = 0.005, 0.01, 0.02, 0.025, 0.03) is 2.6m0, which is 160% higher than that of the p-type AB2X2 alloy.

[0038] Example 4

[0039] Pure elements are classified according to SmMg 2.3 Sb 1.97-y Bi y Te 0.03 Using atomic stoichiometry (y = 0, 0.10, 0.25, and 0.50 respectively), Sm powder, Mg powder, Sb powder, Bi powder, and Te powder were weighed in an argon atmosphere and placed in a ball mill jar for ball milling for 6 hours. The resulting alloy powder was then placed in a graphite mold and sintered for 2 minutes at a sintering temperature of 950℃ and a pressure of 50MPa, followed by furnace cooling to obtain n-type SmMg. 2.3 Sb 1.97-y Bi y Te 0.03 Thermoelectric materials.

[0040] The variable-temperature lattice thermal conductivity curve of this embodiment is as follows: Figure 8 As shown, the zT analysis graph for temperature variation is as follows: Figure 9 As shown, the lattice thermal conductivity of the alloy is significantly optimized after introducing Bi atoms at the Sb site. The substantial reduction in lattice thermal conductivity leads to a significant increase in the zT value of the alloy. Ultimately, SmMg... 2.3 Sb 1.72 Bi 0.25 Te 0.03 The zT value reaches ~1.0 at 873K, which is about 90% higher than that of the matrix.

[0041] The performance of SmMg2Sb2-based materials was compared with that of AB2X2 (1-2-2 type) Zintl phase compounds in the prior art. The maximum zT values ​​of variable-temperature zT analysis were compared with those of other n-type Zintl phase materials in the comparative example. Figure 10 As shown, the currently reported n-type Zintl phases are only Mg3Sb2, KGaSb4, YbMg2Sb2, and KAlSb. 41And Eu5In2As6. Among these alloys, except for Mg3Sb2, the n-type SmMg2Sb2 thermally based material of the present invention has the highest electrical properties.

[0042] The thermoelectric parameters of the SmMg2Sb2-based material in the above embodiments and the AB2X2 (1-2-2 type) Zintl phase compound in the prior art at 700 K are shown in Table 1. It can be seen that the AB2X2 (1-2-2 type) Zintl phase compounds disclosed in the prior art are basically p-type, while the SmMg2Sb2-based material in this embodiment is n-type. The conduction band degeneracy of SmMg2Sb2 is 6. Experimental results show that the effective mass of the density of states of the n-type is 2.6m0, which is higher than all reported p-type AB2X2 alloys. The excellent conduction band structure gives the n-type SmMg2Sb2-based alloy high electrical transport performance. Finally, after adjusting the electron concentration and lattice thermal conductivity, the n-type SmMg2Sb2-based alloy (SmMg 2.3 Sb 1.72 Bi 0.25 Te 0.03 The zT value of ) reaches 1.0 at 873K.

[0043] Table 1

[0044]

[0045] In addition, with the existing technology of K 0.895 Ba 0.015 GaSb4, Yb 0.48 Mg 0.5 Y 0.02 Mg 2.3 Sb2, K 0.990 Ba 0.010 AlSb4, Eu5In 1.85 Zn 0.15 As6 is used as a comparative example, and compared with the above embodiments, zT max The comparison results are shown in Table 2. It can be seen that the SmMg in this embodiment... 2.3 Sb 1.72 Bi 0.25 Te 0.03 With zT max It reached 1.0, higher than other comparative studies.

[0046] Table 2

[0047]

[0048] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. An n-type SmMg2Sb2-based thermoelectric material, characterized in that: Its general chemical formula is SmMg 2.3 Sb 2-x-y Bi y Te x 0 <x≤0.03,0≤y≤0.5。 2. The n-type SmMg2Sb2-based thermoelectric material according to claim 1, characterized in that: Its general chemical formula is SmMg 2.3 Sb2, SmMg 2.3 Sb 2-x Te x or SmMg 2.3 Sb 1.97-y Bi y Te 0.03 , 0≤x≤0.03, 0≤y≤0.

5.

3. The n-type SmMg2Sb2-based thermoelectric material according to claim 2, characterized in that: x is 0, 0.0005, 0.010, 0.020, 0.025 or 0.030, and y is 0, 010, 0.25 or 0.

5.

4. The method for preparing the n-type SmMg2Sb2-based thermoelectric material according to any one of claims 1 to 3, characterized in that: Under an argon atmosphere, Sm powder, Mg powder, Sb powder, Bi powder, and Te powder are weighed according to the stoichiometric ratio of the general chemical formula and placed into a ball mill jar for ball milling for 4-8 hours. The resulting alloy powder is then placed into a graphite mold, heated to 900-1000℃, and sintered for 1.5-3 minutes at a sintering pressure of 40-60 MPa. After furnace cooling, n-type SmMg2Sb2-based thermoelectric material is obtained.

5. The method for preparing n-type SmMg2Sb2-based thermoelectric materials according to claim 4, characterized in that: The sintering temperature is 950℃ and the pressure is 50 MPa.

6. The method for preparing n-type SmMg2Sb2-based thermoelectric materials according to claim 4, characterized in that: The ball milling time is 6 hours.

7. The method for preparing n-type SmMg2Sb2-based thermoelectric materials according to claim 4, characterized in that: In the ball mill jar, the ball-to-material ratio is 1:0.8~1.2.

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