A p-type ybmag2bi2-based thermoelectric material and a preparation method thereof

Abstract

The application discloses a p-type YbMg2Bi2-based thermoelectric material and a preparation method thereof, and belongs to the field of new energy materials. 2+x‑ y Cd y Bi2, wherein 0 x <0.1, 0 y <0.4, and the preparation method is prepared by high-energy ball milling combined with spark plasma sintering.The application constructs a second phase which can be dissolved by adjusting the content of Mg, adjusts the content of the second phase to improve the carrier concentration in the high-temperature region, makes the carrier concentration close to the optimal carrier concentration interval, and thus a higher power factor is still obtained in the high-temperature region. ZT On the other hand, while ensuring the optimal carrier concentration, the lattice thermal conductivity is reduced by alloying Cd to enhance phonon scattering, the lattice thermal conductivity is significantly reduced while maintaining the optimal carrier concentration, and finally the figure of merit of the material is improved. ZT The highest ZT value of the material is 0.8-1.0.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy materials, and in particular to a p-type YbMg2Bi2-based thermoelectric material and a preparation method thereof. BACKGROUND

[0002] Thermoelectric materials can directly realize the mutual conversion between heat and electricity, and have important application value in the fields of low-grade energy recovery and solid-state refrigeration. A thermoelectric material with excellent performance needs to have both high power factor and low total thermal conductivity, but this is usually difficult to achieve due to the strong coupling relationship between the parameters. At present, 1-2-2 type AB2C2-based Zintl compounds have a typical hexagonal layered structure. In the polyanion layer [B2C2] 2- , the B atoms and C atoms are bonded in a covalent bond, which is relatively strong, and the carrier mobility is high, so that the compound has the characteristics of an "electron crystal", that is, in terms of electrical conductivity, it has good electrical transport behavior like a typical crystal; while the cation layer A 2+ is bonded to the polyanion layer [B2C2] 2- in an ionic bond, which is relatively weak, and the sound speed is low, so that the compound exhibits the characteristics of a "phonon glass", that is, in terms of thermal conductivity, it has low thermal transport behavior like glass. The rich bonding modes in AB2C2-based Zintl compounds provide a broad space for independent regulation of electrical and thermal transport behavior, and among them, p-type YbMg2Bi2, as a typical representative of 1-2-2 type Zintl materials, is a promising medium-temperature thermoelectric material. However, the carrier concentration of YbMg2Bi2 material is much lower than the optimal carrier concentration in the entire temperature range, which makes its power factor poor. Not only that, the lattice thermal conductivity of the material is still high, and the ZT value of the pure phase sample is only about 0.5, so obtaining the optimal carrier concentration in the entire temperature range is crucial to improving the application value of YbMg2Bi2. SUMMARY

[0003] One of the purposes of the present application is to provide a p-type YbMg2Bi2-based thermoelectric material to solve the above problems.

[0004] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: a p-type YbMg2Bi2-based thermoelectric material, the chemical general formula of the YbMg2Bi2-based thermoelectric material is YbMg 2+x-y Cd y Bi2, wherein 0 < x < 0.1, 0 ≤ y < 0.4.

[0005] As a preferred technical scheme, x = 0.04, y = 0.2.

[0006] The material of this invention is a polycrystalline bulk material prepared by high-energy ball milling combined with spark plasma sintering; by adjusting the Mg content and Cd element doping, the carrier concentration in the high-temperature region is increased while the lattice thermal conductivity is reduced, thereby improving the thermoelectric performance in the entire temperature range, with a ZT value of 0.8 to 1.0.

[0007] The second objective of this invention is to provide a method for preparing the above-mentioned p-type YbMg2Bi2-based thermoelectric material, comprising the following steps:

[0008] (1) Weigh the reaction raw materials according to the molar ratio of each element in the chemical formula;

[0009] (2) Load the raw materials weighed in step (1) into a stainless steel ball mill jar;

[0010] (3) Place the sealed ball mill jar obtained in step (2) on a ball mill for ball milling to obtain powder;

[0011] (4) Load the powder obtained by ball milling in step (3) into a graphite mold;

[0012] (5) Place the prepared graphite mold from step (4) into a spark plasma sintering furnace for plasma sintering to obtain the desired result.

[0013] As a preferred technical solution, all steps are carried out in a glove box filled with argon gas, wherein the oxygen concentration in the glove box is less than 0.1 ppm and the water concentration is less than 0.1 ppm.

[0014] As a preferred technical solution, in step (2), in addition to the presence of the initial raw material, two stainless steel balls with a mass of 10g and a diameter of 12.7mm are placed in the ball mill jar to crush the raw material.

[0015] As a preferred technical solution, in step (3), the ball milling time is 10 to 12 hours, and the particle size of the resulting powder is about 100 nm to 500 nm.

[0016] As a preferred technical solution, in step (3), the ball mill uses a SPEX8000 high-energy ball mill, wherein the speed of the ball mill motor is not less than 1500 r / min and the operating frequency of the fixture is 875 times / min.

[0017] As a preferred technical solution, in step (5), the discharge plasma sintering temperature is 600℃~650℃, the pressure is 50~60 MPa, and the sintering time is 5~10 min.

[0018] As a further preferred technical solution, the pressurization rate is 10 to 15 MPa / min, and the heating rate is 50 to 100 ℃ / min.

[0019] Compared with the prior art, the advantages of the present invention are as follows: On the one hand, the present invention constructs a resoluble second phase by adjusting the Mg content, and increases the carrier concentration in the high-temperature region by adjusting the content of the second phase, making it close to the optimal carrier concentration range, thereby obtaining a high power factor in the high-temperature region; on the other hand, while ensuring the optimal carrier concentration, Cd alloying is used to enhance phonon scattering and reduce lattice thermal conductivity, thereby significantly reducing lattice thermal conductivity while maintaining an optimal carrier concentration, ultimately improving the ZT value of the material, with the highest ZT value of the material being 0.8 to 1.0. Attached Figure Description

[0020] Figure 1 It is the p-type YbMg prepared in Example 1 2+x-y Cd y XRD patterns of Bi2-based thermoelectric materials;

[0021] Figure 2 It is the p-type YbMg prepared in Example 1 2+x-y Cd y Electrical conductivity curves of Bi2-based thermoelectric materials;

[0022] Figure 3 It is the p-type YbMg prepared in Example 1 2+x-y Cd y Seebeck coefficient curve of Bi2-based thermoelectric materials;

[0023] Figure 4 It is the p-type YbMg prepared in Example 1 2+x-y Cd y Carrier concentration curve of Bi2-based thermoelectric material;

[0024] Figure 5 It is the p-type YbMg prepared in Example 1 2+x-y Cd y Power factor curve of Bi2-based thermoelectric materials;

[0025] Figure 6 It is the p-type YbMg prepared in Example 1 2+x-y Cd y Overall thermal conductivity curve of Bi2-based thermoelectric materials;

[0026] Figure 7 It is the p-type YbMg prepared in Example 1 2+x-y Cd y ZT value curve of Bi2-based thermoelectric material;

[0027] Figure 8 The p-type YbMg prepared in Example 2 2+x-y Cd yXRD patterns of Bi2-based thermoelectric materials;

[0028] Figure 9 The p-type YbMg prepared in Example 2 2+x-y Cd y Electrical conductivity curves of Bi2-based thermoelectric materials;

[0029] Figure 10 The p-type YbMg prepared in Example 2 2+x-y Cd y Power factor curve of Bi2-based thermoelectric materials;

[0030] Figure 11 The p-type YbMg prepared in Example 2 2+x-y Cd y Carrier concentration curve of Bi2-based thermoelectric material;

[0031] Figure 12 The p-type YbMg prepared in Example 2 2+x-y Cd y Power factor curve of Bi2-based thermoelectric materials;

[0032] Figure 13 The p-type YbMg prepared in Example 2 2+x-y Cd y Overall thermal conductivity curve of Bi2-based thermoelectric materials;

[0033] Figure 14 The p-type YbMg prepared in Example 2 2+x-y Cd y ZT value curve of Bi2-based thermoelectric material;

[0034] Figure 15 The p-type YbMg prepared in Example 3 2+x-y Cd y XRD patterns of Bi2-based thermoelectric materials;

[0035] Figure 16 The p-type YbMg prepared in Example 3 2+x-y Cd y Electrical conductivity curves of Bi2-based thermoelectric materials;

[0036] Figure 17 The p-type YbMg prepared in Example 3 2+x-y Cd y Power factor curve of Bi2-based thermoelectric materials;

[0037] Figure 18 The p-type YbMg prepared in Example 3 2+x-y Cd y Carrier concentration curve of Bi2-based thermoelectric material;

[0038] Figure 19 The p-type YbMg prepared in Example 3 2+x-y Cd y Power factor curve of Bi2-based thermoelectric materials;

[0039] Figure 20 The p-type YbMg prepared in Example 3 2+x-y Cd y Overall thermal conductivity curve of Bi2-based thermoelectric materials;

[0040] Figure 21 The p-type YbMg prepared in Example 3 2+x-y Cd y ZT value curve of Bi2-based thermoelectric material;

[0041] Figure 22 p-type YbMg prepared in Comparative Example 1 2+x-y Cd y XRD patterns of Bi2-based thermoelectric materials;

[0042] Figure 23 p-type YbMg prepared in Comparative Example 1 2+x-y Cd y Electrical conductivity curves of Bi2-based thermoelectric materials;

[0043] Figure 24 p-type YbMg prepared in Comparative Example 1 2+x-y Cd y Seebeck coefficient curve of Bi2-based thermoelectric materials;

[0044] Figure 25 p-type YbMg prepared in Comparative Example 1 2+x-y Cd y Carrier concentration curve of Bi2-based thermoelectric material;

[0045] Figure 26 p-type YbMg prepared in Comparative Example 1 2+x-y Cd y Power factor curve of Bi2-based thermoelectric materials;

[0046] Figure 27 p-type YbMg prepared in Comparative Example 1 2+x-y Cd y Overall thermal conductivity curve of Bi2-based thermoelectric materials;

[0047] Figure 28 p-type YbMg prepared in Comparative Example 1 2+x-y Cd y ZT value curve of Bi2-based thermoelectric material

[0048] Figure 29 p-type YbMg prepared in Comparative Example 2 2+x-y Cd y XRD patterns of Bi2-based thermoelectric materials;

[0049] Figure 30 p-type YbMg prepared in Comparative Example 2 2+x-y Cd y Electrical conductivity curves of Bi2-based thermoelectric materials;

[0050] Figure 31 p-type YbMg prepared in Comparative Example 2 2+x-y Cd y Power factor curve of Bi2-based thermoelectric materials;

[0051] Figure 32 p-type YbMg prepared in Comparative Example 2 2+x-y Cd y Carrier concentration curve of Bi2-based thermoelectric material;

[0052] Figure 33 p-type YbMg prepared in Comparative Example 2 2+x-y Cd y Power factor curve of Bi2-based thermoelectric materials;

[0053] Figure 34 p-type YbMg prepared in Comparative Example 2 2+x-y Cd y Overall thermal conductivity curve of Bi2-based thermoelectric materials;

[0054] Figure 35 p-type YbMg prepared in Comparative Example 2 2+x-y Cd y ZT value curve of Bi2-based thermoelectric material. Detailed Implementation

[0055] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the present invention is not limited to the following embodiments.

[0056] Example 1

[0057] A p-type YbMg2Bi2-based thermoelectric material is prepared by following these steps:

[0058] (1) According to YbMg 2+x-y Cd y The raw materials were weighed according to the general chemical formula of Bi2, where x = 0.02 and y = 0; and the mass purity of elements Yb, Mg, and Bi was better than 99.9%.

[0059] (2) Raw material ball milling: In a glove box filled with argon (oxygen concentration less than 0.1 ppm, water concentration less than 0.1 ppm), the raw material described in step (1) and two stainless steel balls with a diameter of 12.7 mm are sealed in a stainless steel ball mill jar; then it is placed on a high-energy ball mill for vibration crushing, wherein the speed of the ball mill motor is not less than 1500 r / min, the operating frequency of the clamp is 875 times / min, and the ball milling time is 11 h;

[0060] (3) Sintering: In a glove box, the powder obtained in step (2) is loaded into a graphite mold with a diameter of 12.7 mm. In a spark plasma sintering furnace, the powder is heated at a heating rate of 50℃ / min and pressurized at a pressurization rate of 10 MPa / min. Finally, the powder is held at 650℃ and 50 MPa axial pressure for 5 min to obtain a sample with a density of 96% or higher.

[0061] The YbMg obtained in this embodiment 2+x-y Cd y The XRD diffraction pattern of the Bi2-based thermoelectric material is shown in [reference needed]. Figure 1 It can be seen that YbMg 2.02 In addition to the main phase structure, the Bi2 thermoelectric material also contains a Bi second phase. The electrical conductivity and Seebeck coefficient of the samples are shown in the table below. Figure 2 and Figure 3 As can be seen, the room temperature conductivity and Seebeck coefficient of the sample are 380.2 S / cm and 179.3 μV / K, respectively, while the conductivity and Seebeck coefficient at 873 K are 614.3 S / cm and 150.3 μV / K, respectively. The positive Seebeck coefficient indicates that the prepared sample is a p-type material. The relationship between the carrier concentration and temperature of the sample is shown in [Figure showing the relationship between the carrier concentration and temperature]. Figure 4 The carrier concentration at room temperature of the sample is Approaching the optimal carrier concentration range for YbMg2Bi2-based materials The carrier concentration at 723 K is Approaching the optimal carrier concentration range for YbMg2Bi2-based materials at 723 K. The power factor of the sample is shown in [reference needed]. Figure 5 The room temperature power factor is 12.2 μW / mK. 2 The power factor at 873 K is 13.9 μW / mK. 2 Its total thermal conductivity is shown in the figure. Figure 6 The total thermal conductivity at room temperature is 2.9 W / mK, and at 873 K it is 1.4 W / mK; finally, its ZT value changes with temperature as follows: Figure 7 As shown, the ZT of the sample at 873 K is 0.84.

[0062] Compared to Comparative Example 1 described later, YbMg does not contain a Bi second phase. 2.12 Compared to the Bi2 sample, this embodiment has YbMg 2.02 Bi2 contains a second phase of Bi. At high temperatures, this second phase dissolves, increasing the high-temperature carrier concentration to near its optimal range. This leads to increased high-temperature conductivity and a decreased Seebeck coefficient, ultimately resulting in the degradation of YbMg. 2.02 The ZT value of the Bi2 sample is higher than that of the YbMg sample. 2.12 Bi2 (ZT = 0.44@873 K). Its performance variations and comparisons are shown in [link to relevant documentation]. Figures 1-7 and Figures 22-28 .

[0063] Example 2

[0064] The difference between this embodiment and embodiment 1 is that the components x and y shown in step 1) are 0.04 and 0.2 respectively, while the other experimental steps are the same as in embodiment 1.

[0065] The YbMg obtained in this embodiment 2+x-y Cd y The XRD diffraction pattern of the Bi2-based thermoelectric material is shown in [reference needed]. Figure 8 It can be seen that YbMg 1.84 Cd 0.2 In addition to the main YbMg2Bi2 structure, the Bi2-based thermoelectric material also contains a Bi impurity phase. The electrical conductivity and Seebeck coefficient of the samples are shown in the table below. Figure 9 and Figure 10 As can be seen, the room temperature conductivity and Seebeck coefficient of the sample are 360.4 S / cm and 167.3 μV / K, respectively, while the conductivity and Seebeck coefficient at 873 K are 547.2 S / cm and 165.0 μV / K, respectively. The relationship between the carrier concentration of the sample and temperature is shown in the figure. Figure 11 The carrier concentration at room temperature of the sample is Approaching the optimal carrier concentration range for YbMg2Bi2-based materials Carrier concentration at 723 K Approaching the optimal carrier concentration range for YbMg2Bi2-based materials at 723 K. The power factor of the sample is shown in [reference needed]. Figure 12 The room temperature power factor is 10.0 μW / mK. 2 The power factor at 873 K is 14.9 μW / mK. 2 The total thermal conductivity of the sample is shown in the figure. Figure 13 Its total thermal conductivity at room temperature is 1.5 W / mK, and at 873 K it is 1.3 W / mK. Due to the enhanced scattering of point defects after Cd alloying, the total thermal conductivity is significantly reduced. Ultimately, its ZT value changes with temperature as follows:Figure 14 As shown, the ZT value at 873 K is as high as 1.0.

[0066] Example 3

[0067] The difference between this embodiment and Embodiment 1 is that the components x and y shown in step 1) are 0.08 and 0.3 respectively, while the other experimental steps are the same as in Embodiment 1.

[0068] The YbMg obtained in this embodiment 2+x-y Cd y The XRD diffraction pattern of the Bi2-based thermoelectric material is shown in [reference needed]. Figure 15 It can be seen that YbMg 1.78 Cd 0.3 In addition to the main YbMg2Bi2 structure, the Bi2 thermoelectric material also contains a Bi impurity phase. The electrical conductivity and Seebeck coefficient of the samples are shown in the table below. Figure 16 and Figure 17 As can be seen, the room temperature conductivity and Seebeck coefficient of the sample are 345.9 S / cm and 164.0 μV / K, respectively, while the conductivity and Seebeck coefficient at 873 K are 525.3 S / cm and 161.7 μV / K, respectively. The relationship between the carrier concentration of the sample and temperature is shown in the figure. Figure 18 The carrier concentration at room temperature of the sample is Approaching the optimal carrier concentration range for YbMg2Bi2-based materials The carrier concentration at 723 K is Approaching the optimal carrier concentration range for YbMg2Bi2-based materials at 723 K. The power factor of the sample is shown in [reference needed]. Figure 19 The room temperature power factor is 9.3 μW / mK. 2 The power factor at 873 K is 13.7 μW / mK. 2 The total thermal conductivity of the sample is shown in the figure. Figure 20 Its total thermal conductivity at room temperature is 1.5 W / mK, and at 873 K it is 1.28 W / mK; finally, its ZT value changes with temperature as follows: Figure 21 As shown, the ZT value at 873 K is 0.99. However, in Comparative Example 2 described later, a dopant content exceeding the optimal range was selected. Figures 29-35 It was found that the sample had poor electrical transport properties, resulting in a low ZT value of 0.52 at 873 K. This demonstrates that, when doping elements, the appropriate doping concentration is crucial for obtaining high-performance YbMg2Bi2-based materials.

[0069] Comparative Example 1

[0070] The difference between this comparative example and Example 1 is that the components x and y shown in step 1) are 0.12 and 0, respectively, while the other experimental steps are the same as in Example 1.

[0071] The YbMg obtained in this comparative example 2+x-y Cd y The XRD diffraction pattern of the Bi2-based thermoelectric material is shown in [reference needed]. Figure 22 It can be seen that YbMg 2.12 Bi2 only has the main phase YbMg2Bi2 structure and no other impurity phases. The electrical conductivity and Seebeck coefficient of the sample are shown in the following figures. Figure 23 and Figure 24 As can be seen, the room temperature conductivity and Seebeck coefficient of the sample are 166.9 S / cm and 242.2 μV / K, respectively, while the conductivity and Seebeck coefficient at 873 K are 116.2 S / cm and 234.9 μV / K, respectively. The relationship between the carrier concentration of the sample and temperature is shown in the figure. Figure 25 The carrier concentration at room temperature of the sample is This deviates from the optimal carrier concentration range for YbMg2Bi2-based materials at room temperature. The carrier concentration at 723 K is The value is lower than that of YbMg in Example 1. 2.02 The carrier concentration of the Bi2 sample at 723 K is much smaller than the optimal carrier concentration range for YbMg2Bi2-based materials at 723 K. The power factor of the sample is shown in [reference needed]. Figure 26 The room temperature power factor is 9.8 μW / mK. 2 The power factor at 873 K is 6.4 μW / mK. 2 Total thermal conductivity is shown in Figure 27 The total thermal conductivity at room temperature is 2.7 W / mK, and at 873 K it is 1.3 W / mK; finally, its ZT value changes with temperature as follows: Figure 28 As shown, the ZT value at 873 K is 0.44.

[0072] Comparative Example 2

[0073] The difference between Comparative Example 2 and Example 1 is that the components x and y shown in step 1) are 0.1 and 0.5 respectively, while the other experimental steps are the same as in Example 1.

[0074] The YbMg obtained in this embodiment 2+x-y Cd y The XRD diffraction pattern of the Bi2-based thermoelectric material is shown in [reference needed]. Figure 29 It can be seen that YbMg 1.6 Cd 0.5The Bi2 thermoelectric material consists only of a YbMg2Bi2 structure and contains no second phase. The electrical conductivity and Seebeck coefficient of the sample are shown in the figures below. Figure 30 and Figure 31 As can be seen, the room temperature conductivity and Seebeck coefficient of the sample are 217.0 S / cm and 218.0 μV / K, respectively, while the conductivity and Seebeck coefficient at 873 K are 151.1 S / cm and 211.4 μV / K, respectively. The relationship between the carrier concentration of the sample and temperature is shown in the figure. Figure 32 The carrier concentration at room temperature of the sample is This deviates from the optimal carrier concentration range for YbMg2Bi2-based materials at room temperature. The carrier concentration at 723 K is This deviates from the optimal carrier concentration range for YbMg2Bi2-based materials at 723 K. The power factor of the sample is shown in [reference needed]. Figure 33 The room temperature power factor is 12.7 μW / mK. 2 The power factor at 873 K is 8.3 μW / mK. 2 Total thermal conductivity is shown in Figure 34 The total thermal conductivity at room temperature is 1.65 W / mK, and at 873 K it is 1.4 W / mK; finally, its ZT value changes with temperature as follows: Figure 35 As shown, the ZT value at 873 K is 0.52.

[0075] Table 1 shows the room temperature carrier concentration, high temperature carrier concentration, and ZT value in different embodiments and comparative examples. It can be seen that constructing the Bi second phase to promote its high temperature re-dissolution can effectively improve the high temperature carrier concentration and ZT value. At the same time, the introduction of Cd elements into point defects significantly reduces the total thermal conductivity and enhances the thermoelectric figure of merit of the material. Appropriate Mg and Cd content in the samples is crucial for obtaining ZT values ​​in the range of 0.8–1.0.

[0076] Table 1. Comparison of room temperature carrier concentration, high temperature carrier concentration, and ZT value in different embodiments and comparative examples.

[0077]

[0078] 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 p-type YbMg2Bi2-based thermoelectric material, characterized in that, The general chemical formula of the YbMg2Bi2-based thermoelectric material is YbMg 2+x-y Cd y Bi2, where x=0.02 and y=0, or x=0.04 and y=0.2, or x=0.08 and y=0.3; Its preparation method includes the following steps: (1) Weigh the reaction raw materials according to the molar ratio of each element in the general chemical formula; (2) Load the raw materials weighed in step (1) into a stainless steel ball mill jar; (3) Place the sealed ball mill jar obtained in step (2) on a ball mill for ball milling to obtain powder; (4) Load the powder obtained by ball milling in step (3) into a graphite mold; (5) Place the prepared graphite mold from step (4) into a spark plasma sintering furnace for plasma sintering to obtain the desired result.

2. The p-type YbMg2Bi2-based thermoelectric material according to claim 1, characterized in that, All steps were carried out in an argon-filled glove box with an oxygen concentration of less than 0.1 ppm and a water concentration of less than 0.1 ppm.

3. The p-type YbMg2Bi2-based thermoelectric material according to claim 1, characterized in that, In step (3), the ball milling time is 10 to 12 hours, and the particle size of the resulting powder is 100 nm to 500 nm.

4. The p-type YbMg2Bi2-based thermoelectric material according to claim 1, characterized in that, In step (3), the ball mill uses a SPEX8000 high-energy ball mill, wherein the speed of the ball mill motor is not less than 1500 r / min and the operating frequency of the fixture is 875 times / min.

5. The p-type YbMg2Bi2-based thermoelectric material according to claim 1, characterized in that, In step (5), the discharge plasma sintering temperature is 600℃~650℃, the pressure is 50~60 MPa, and the sintering time is 5~10 min.

6. The p-type YbMg2Bi2-based thermoelectric material according to claim 5, characterized in that, in, The pressurization rate is 10–15 MPa / min, and the heating rate is 50–100 °C / min.

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