A p-type CaMg2Sb2-based thermoelectric material and its preparation method

Abstract

The present invention discloses a p-type CaMg2Sb2-based thermoelectric material and a preparation method thereof, belonging to the field of new energy materials. The chemical composition of the CaMg2Sb2-based thermoelectric material is: Ca 1‑x‑ y Yb x Li y Mg 2‑z Cd z Sb2, where 0 < x < 0.7, 0 < y < 0.03, 0 < z ≤ 0.5; the preparation method is to prepare by high-energy ball milling and spark plasma sintering; the p-type CaMg2Sb2-based thermoelectric material provided by the present invention significantly improves the carrier concentration and mobility of the material and reduces the lattice thermal conductivity of the material by co-doping with Yb, Li, and Cd. The highest ZT of the material is between 0.9 and 1.1; the present invention realizes the preparation of a p-type CaMg2Sb2-based thermoelectric material with high carrier concentration and high mobility, and its thermoelectric performance is significantly improved.

Description

Technical Field

[0001] The present invention relates to the field of new energy materials, and in particular to a p-type CaMg2Sb2-based thermoelectric material and a preparation method thereof. Background Art

[0002] The crystal structure of AB2X2-type Zintl compounds is a hexagonal layered structure with the space group P-3m1. Among them, the cation A 2 + layers and [B2X2] 2- layers are combined by ionic bonds, and the ionic bonds can serve as channels for phonon transmission, endowing the compound with the property of "phonon glass"; while the B atoms and X atoms in the polyanion layer are combined by covalent bonds, and the existence of covalent bonds can ensure the high electron mobility of the compound, which is an embodiment of "electronic crystal". Due to the existence of multiple chemical bonds and multiple ionic positions in this type of material, its thermoelectric performance has a very large tunability.

[0003] Currently, the research on AB2X2-type Zintl compounds mainly focuses on p-type YbZn2Sb2 and p-type YbCd2Sb2-based thermoelectric materials. Recently, CaMg2Sb2 thermoelectric materials have attracted much attention due to their low cost and softer ionic bonds. However, the intrinsic carrier concentration and mobility of such materials are very low, and the lattice thermal conductivity is high, resulting in poor intrinsic properties of the materials. Currently, although various optimization strategies have been implemented, the highest thermoelectric performance of p-type CaMg2Sb2 materials only reaches 0.85, which limits its large-scale application. Summary of the Invention

[0004] The purpose of the present invention is to provide a new p-type CaMg2Sb2-based thermoelectric material to solve the above problems.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A p-type CaMg2Sb2-based thermoelectric material, the chemical composition of the CaMg2Sb2-based thermoelectric material is: Ca 1-x-y Yb x Li y Mg 2-z Cd z Sb2, where 0 < x < 0.7, 0 < y < 0.03, 0 < z ≤ 0.5.

[0006] As a preferred technical solution, 0.2 < x < 0.5, 0.01 < y < 0.02, 0.3 < z < 0.5.

[0007] Through a large number of theoretical and experimental studies, the inventors of this application have found that doping to increase the carrier concentration and mobility while reducing the lattice thermal conductivity is the key way to improve the CaMg2Sb2 material. Specifically, in this application, Yb, Li, and Cd are co-doped. Among them, an appropriate amount of Yb and Li are used to partially replace Ca, and an appropriate amount of Cd is used to partially replace Mg, significantly increasing the carrier concentration and mobility of the material and reducing the lattice thermal conductivity of the material, thus achieving an improvement in thermoelectric performance.

[0008] The second object of the present invention is to provide a method for preparing the above-mentioned p-type CaMg2Sb2-based thermoelectric material. The technical solution adopted is that the method includes the following steps:

[0009] 1) Weighing the reaction raw materials according to the molar ratio of each element in the chemical formula;

[0010] 2) Sealing the reaction raw materials obtained in step 1) in a ball milling jar;

[0011] 3) Placing the sealed ball milling jar obtained in step 2) on a ball mill to mill the raw materials to obtain powder;

[0012] 4) Loading the powder obtained in step 3) into a graphite mold;

[0013] 5) Placing the graphite mold obtained in step 4) in a spark plasma sintering furnace for sintering.

[0014] As a preferred technical solution, in step 2), the sealing of the raw materials into the ball milling jar is carried out in a glove box.

[0015] As a further preferred technical solution, the oxygen concentration in the glove box is lower than 0.1 ppm, and the water concentration is lower than 0.1 ppm.

[0016] As a preferred technical solution, in step 3), a high-energy ball mill is used during the ball milling, the rotational speed of the ball mill is about 1500 r / min, and the ball milling time is 12 - 15 h.

[0017] As a preferred technical solution, in step 4), loading the powder into the graphite mold is completed in a glove box filled with argon.

[0018] As a further preferred technical solution, the oxygen concentration in the glove box is lower than 0.1 ppm, and the water concentration is lower than 0.1 ppm.

[0019] As a preferred technical solution, in step 5), the spark plasma sintering process is as follows: under the condition of less than 20 Pa, first pressurize to 5 - 10 MPa; then heat up to 500 - 600 °C and pressurize to 50 - 70 MPa; subsequently, keep the pressure and temperature for 5 - 10 min, and then reduce the pressure and temperature after the pressure and temperature holding ends.

[0020] As a further preferred technical solution, all the pressurization rates are 5 - 10 MPa / min, and the heating rate is 50 - 100 °C / min

[0021] Compared with the prior art, the advantages of the present invention are as follows:

[0022] On the one hand, for the p-type CaMg2Sb2-based thermoelectric material provided by the present invention, the co-doping of Yb, Li, and Cd significantly increases the carrier concentration and mobility of the material, obtaining a better electrical transport performance; on the other hand, the substitution of heavy elements Yb and Cd for Ca sites and Mg sites can enhance phonon scattering, significantly reducing the lattice thermal conductivity of the material, and the highest ZT of the material is 0.9 - 1.1. Description of the Drawings

[0023] Figure 1 is the XRD pattern of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 1;

[0024] Figure 2 is the graph of the conductivity of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 1 varying with temperature;

[0025] Figure 3 is the graph of the Seebeck coefficient of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 1 varying with temperature;

[0026] Figure 4 is the graph of the power factor of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 1 varying with temperature;

[0027] Figure 5 is the graph of the lattice thermal conductivity of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 1 varying with temperature;

[0028] Figure 6 is the graph of the ZT value of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 1 varying with temperature;

[0029] Figure 7 is the XRD pattern of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 2;

[0030] Figure 8 is the graph of the conductivity of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 2 varying with temperature;

[0031] Figure 9 is the graph of the Seebeck coefficient of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 2 varying with temperature;

[0032] Figure 10It is a graph showing the variation of the power factor of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 2 with temperature;

[0033] Figure 11 It is a graph showing the variation of the lattice thermal conductivity of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 2 with temperature;

[0034] Figure 12 It is a graph showing the variation of the ZT value of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 2 with temperature;

[0035] Figure 13 It is the XRD pattern of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 3;

[0036] Figure 14 It is a graph showing the variation of the electrical conductivity of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 3 with temperature;

[0037] Figure 15 It is a graph showing the variation of the Seebeck coefficient of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 3 with temperature;

[0038] Figure 16 It is a graph showing the variation of the power factor of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 3 with temperature;

[0039] Figure 17 It is a graph showing the variation of the lattice thermal conductivity of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 3 with temperature;

[0040] Figure 18 It is a graph showing the variation of the ZT value of the p-type CaMg2Sb2-based thermoelectric material prepared in Comparative Example 3 with temperature;

[0041] Figure 19 It is the XRD pattern of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 1;

[0042] Figure 20 It is a graph showing the variation of the electrical conductivity of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 1 with temperature;

[0043] Figure 21 It is a graph showing the variation of the Seebeck coefficient of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 1 with temperature;

[0044] Figure 22 It is a graph showing the variation of the power factor of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 1 with temperature;

[0045] Figure 23 It is a graph showing the variation of the lattice thermal conductivity of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 1 with temperature;

[0046] Figure 24 It is a graph showing the variation of the ZT value of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 1 with temperature;

[0047] Figure 25 It is the XRD pattern of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 2;

[0048] Figure 26 It is a graph showing the variation of the conductivity of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 2 with temperature;

[0049] Figure 27 It is a graph showing the variation of the Seebeck coefficient of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 2 with temperature;

[0050] Figure 28 It is a graph showing the variation of the power factor of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 2 with temperature;

[0051] Figure 29 It is a graph showing the variation of the lattice thermal conductivity of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 2 with temperature;

[0052] Figure 30 It is a graph showing the variation of the ZT value of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 2 with temperature;

[0053] Figure 31 It is the XRD pattern of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 3;

[0054] Figure 32 It is a graph showing the variation of the conductivity of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 3 with temperature;

[0055] Figure 33 It is a graph showing the variation of the Seebeck coefficient of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 3 with temperature;

[0056] Figure 34 It is a graph showing the variation of the power factor of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 3 with temperature;

[0057] Figure 35 It is a graph showing the variation of the lattice thermal conductivity of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 3 with temperature;

[0058] Figure 36 It is a graph showing the variation of the ZT value of the p-type CaMg2Sb2-based thermoelectric material prepared in Example 3 with temperature. Detailed implementation manners

[0059] The present invention will be further described below with reference to the accompanying drawings.

[0060] Example 1

[0061] A CaMg2Sb2-based thermoelectric material, the preparation method of which comprises the following steps:

[0062] 1) Ingredients: According to the chemical composition Ca 1-x-y Yb x Li y Mg 2-z Cd z Sb2 ingredients, where x, y, z are 0.3, 0.01, 0.5 respectively, the mass purity of Ca, Yb, Li is better than 99.5%, and the mass purity of Mg, Cd, Sb is better than 99.9%;

[0063] 2) Ball milling the raw materials: The reaction raw materials of step 1) are sealed in a stainless steel ball milling jar in a glove box filled with argon, wherein the oxygen concentration in the glove box is less than 0.1 ppm and the water concentration is less than 0.1 ppm; then the stainless steel ball milling jar is placed in a high-energy ball mill and ball milled for 12 h, wherein the rotation speed of the high-energy ball mill is not less than 1500 r / min;

[0064] 3) Loading powder into a graphite mold: loading the raw material obtained by ball milling in step 2) into a graphite mold in a glove box filled with argon, wherein the oxygen concentration in the glove box is less than 0.1 ppm and the water concentration is less than 0.1 ppm;

[0065] 4) Sintering into blocks: The powder is sintered into blocks by spark plasma sintering in a vacuum environment. The specific steps are as follows: first, the vacuum is evacuated to below 20 Pa, and then the graphite mold is pressurized to 10 MPa at a rate of 5 MPa / min, and then the temperature is increased to 550°C at a rate of 80°C / min, and the pressure is increased to 70 MPa at a rate of 5 MPa / min. The temperature and pressure are maintained for 10 min. After the pressure and pressure are maintained, the pressure is reduced and the temperature is reduced to obtain a block sample.

[0066] The XRD spectrum of the CaMg2Sb2-based thermoelectric material obtained in this example is shown in Figure 19 ,from Figure 19 It can be seen that the obtained Ca 0.69 Yb 0.3 Li 0.01 Mg 1.5 Cd 0.5 Sb2-based thermoelectric materials are single-phase; the relationship between conductivity and Seebeck coefficient with temperature is shown in Figure 20 and Figure 21 The room temperature conductivity of the sample is 101.3 S / cm, the Seebeck coefficient is 207.8 μV / K, and the Seebeck coefficient is positive, indicating that it is p-type; its power factor is shown in Figure 22, the room-temperature power factor is 4.4 μW / mK 2 , the power factor can reach 7.5 μW / mK at 773 K 2 . See the lattice thermal conductivity graph in Figure 23 , the room-temperature lattice thermal conductivity is 0.82 W / mK, and the lattice thermal conductivity at 773 K is 0.45 W / mK. Its ZT value changes with temperature as shown in Figure 24 . The maximum ZT value can reach 1.1, making it a high-performance thermoelectric material. It represents an increase of approximately 3566% compared to the ZT value of the sample in Comparative Example 1 described below, and an increase of approximately 57% compared to the ZT value (ZT = 0.70) of the Li and Cd double-doped sample in Comparative Example 2 described below. From Figure 1-12 and Figure 19-24 comparison, it is found that compared with the undoped sample and the double-doped sample, the doping of Yb, Li, and Cd plays an important role in optimizing the electrical transport properties, reducing the lattice thermal conductivity, and increasing the ZT value.

[0067] Example 2

[0068] A CaMg2Sb2-based thermoelectric material, and its preparation method includes the following steps:

[0069] The difference between this Example 2 and Example 1 is that the components x, y, and z shown in step 1) are 0.5, 0.015, and 0.3 respectively, and the other experimental procedure flows are the same as those in Example 1.

[0070] The XRD pattern of the CaMg2Sb2-based thermoelectric material obtained in this Example 2 is shown in Figure 25 , Ca 0.485 Yb 0.5 Li 0.015 Mg 1.7 Cd 0.3 Sb2 thermoelectric material is single-phase; the variation relationships of the conductivity and Seebeck coefficient with temperature are shown in Figure 26 and Figure 27 . The room-temperature conductivity of the sample is 69.2 S / cm, the Seebeck is 191.1 μV / K, and the Seebeck coefficient is positive, indicating that it is p-type; its power factor is shown in Figure 28 , the room-temperature power factor is 2.5 μW / mK 2 , the power factor can reach 6.6 μW / mK at 773 K 2 . See the lattice thermal conductivity graph in Figure 29 , the room-temperature lattice thermal conductivity is 0.82 W / mK, and the lattice thermal conductivity at 773 K is 0.47 W / mK. Its ZT value changes with temperature as shown in Figure 30 . The maximum ZT value can reach 0.9, making it a high-performance thermoelectric material.

[0071] Example 3

[0072] A preparation method of a CaMg2Sb2-based thermoelectric material, comprising the following steps:

[0073] The difference between Example 3 and Example 1 is that the components x, y, and z shown in step 1) are 0.2, 0.02, and 0.45 respectively. The other experimental procedure flows are the same as those in Example 1.

[0074] The XRD pattern of the CaMg2Sb2-based thermoelectric material obtained in this Example 3 is shown in Figure 31 , Ca 0.78 Yb 0.2 Li 0.02 Mg 1.55 Cd 0.45 The Sb2 thermoelectric material is single-phase; the variation relationships of the electrical conductivity and the Seebeck coefficient with temperature are shown in Figure 32 and Figure 33 , the room-temperature electrical conductivity of the sample is 59 S / cm, the Seebeck coefficient is 244 μV / K, and the Seebeck coefficient is positive, indicating that it is p-type; its power factor is shown in Figure 34 , the room-temperature power factor is 3.4 μW / mK 2 , and the power factor can reach 10.0 μW / mK at 773 K 2 . The lattice thermal conductivity graph is shown in Figure 35 , the room-temperature lattice thermal conductivity is 0.93 W / mK, the lattice thermal conductivity at 773 K is 0.46 W / mK, and the variation of its ZT value with temperature is as shown in Figure 36 , the maximum ZT value can reach 1.0, which is a thermoelectric material with excellent performance. In Comparative Example 3 described later, doping element contents beyond the preferred range are selected, and it is found from Figure 13-18 that the electrical transport performance of the sample is poor, resulting in its ZT value being only 0.46 at 773 K. Thus, it can be seen that when doping with three elements, appropriate doping contents are the key to obtaining high-performance CaMg2Sb2-based materials.

[0075] Comparative Example 1

[0076] A preparation method of a CaMg2Sb2-based thermoelectric material, comprising the following steps:

[0077] The difference between this comparative example and Example 1 is that the components x, y, and z shown in step 1) are 0, 0, and 0 respectively. The other experimental procedure flows are the same as those in Example 1.

[0078] The XRD pattern of the CaMg2Sb2-based thermoelectric material obtained in this comparative example is shown in Figure 1 , the CaMg2Sb2 thermoelectric material is single-phase; the variation relationships of the electrical conductivity and the Seebeck coefficient with temperature are shown in Figure 2 and Figure 3, the room-temperature electrical conductivity of the sample is 0.01 S / cm, the Seebeck coefficient is 601 μV / K, and the Seebeck coefficient is positive, indicating that it is p-type; its power factor is shown in Figure 4 , and the room-temperature power factor is 0.04 μW / mK 2 , and the power factor can reach 0.7 μW / mK at 773 K 2 . The lattice thermal conductivity diagram is shown in Figure 5 , the room-temperature lattice thermal conductivity is 4.0 W / mK, the lattice thermal conductivity at 773 K is 1.5 W / mK, and its ZT value changes with temperature as shown in Figure 6 . The ZT value is 0.03 at 773 K

[0079] Comparative Example 2

[0080] A preparation method of a CaMg2Sb2-based thermoelectric material includes the following steps:

[0081] The difference between this comparative example and Example 1 is that the components x, y, and z shown in step 1) are 0, 0.01, and 0.5 respectively. The other experimental procedure flows are the same as those in Example 1

[0082] The XRD pattern of the CaMg2Sb2-based thermoelectric material obtained in this comparative example is shown in Figure 7 , Ca 0.99 Li 0.01 Mg 1.5 Cd 0.5 The Sb2 thermoelectric material is single-phase; the variation relationships of the electrical conductivity and the Seebeck coefficient with temperature are shown in Figure 8 and Figure 9 , the room-temperature electrical conductivity of the sample is 15.6 S / cm, the Seebeck coefficient is 344.7 μV / K, and the Seebeck coefficient is positive, indicating that it is p-type; its power factor is shown in Figure 10 , and the room-temperature power factor is 1.9 μW / mK 2 , and the power factor can reach 5.2 μW / mK at 773 K 2 . The lattice thermal conductivity diagram is shown in Figure 11 , the room-temperature lattice thermal conductivity is 0.99 W / mK, the lattice thermal conductivity at 773 K is 0.53 W / mK, and its ZT value changes with temperature as shown in Figure 12 . The ZT value is 0.69 at 773 K

[0083] Comparative Example 3

[0084] A preparation method of a CaMg2Sb2-based thermoelectric material includes the following steps:

[0085] The difference between this comparative example and Example 1 is that the components x, y, and z shown in step 1) are 0.7, 0.01, and 0.65 respectively. The other experimental procedure flows are the same as those in Example 1

[0086] The XRD pattern of the CaMg2Sb2-based thermoelectric material obtained in this comparative example is shown in Figure 13 , Ca 0.29 Yb 0.7 Li 0.01 Mg 1.35 Cd 0.65 The Sb2 thermoelectric material is single-phase; the variation relationships of the electrical conductivity and Seebeck coefficient with temperature are shown in Figure 14 and Figure 15 . The room-temperature electrical conductivity of the sample is 13.1 S / cm, the Seebeck coefficient is 231 μV / K, and the Seebeck coefficient is positive, indicating that it is p-type; its power factor is shown in Figure 16 . The room-temperature power factor is 0.7 μW / mK 2 , and the power factor can reach 5.7 μW / mK at 773 K 2 . The lattice thermal conductivity diagram is shown in Figure 17 . The room-temperature lattice thermal conductivity is 1 W / mK, and the lattice thermal conductivity at 773 K is 0.89 W / mK. The variation of its ZT value with temperature is as shown in Figure 18 . The ZT value is 0.43 at 773 K.

[0087] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, several improvements and transformations can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A p-type CaMg2Sb2-based thermoelectric material, characterized in that, The chemical composition of the CaMg2Sb2-based thermoelectric material is: Ca 1-x-y Yb x Li y Mg 2-z Cd z Sb2, where 0 < x < 0.7, 0 < y < 0.03, 0 < z ≤ 0.

5.

2. The p-type CaMg2Sb2-based thermoelectric material according to claim 1, characterized in that 0.2 ＜ x ＜ 0.5，0.01＜ y ＜ 0.02，0.3 ＜ z ＜ 0.5。 3. The preparation method of the p-type CaMg2Sb2-based thermoelectric material according to claim 1 or 2, characterized in that, The method includes the following steps: 1) Ingredients preparation: Weigh the reaction raw materials according to the proportion of the amount of substances of each element in the chemical formula; 2) Seal the reaction raw materials described in step 1) in a ball milling jar; 3) Place the sealed ball milling jar obtained in step 2) on a ball mill to mill the raw materials to obtain powder; 4) Load the powder obtained in step 3) into a graphite mold; 5) Place the graphite mold in step 4) in a spark plasma for sintering.

4. The preparation method of the p-type CaMg2Sb2-based thermoelectric material according to claim 3, characterized in that, In step 2), the sealing of the raw materials into the ball milling jar is carried out in a glove box.

5. The preparation method of the p-type CaMg2Sb2-based thermoelectric material according to claim 4, wherein, The oxygen concentration in the glove box is lower than 0.1 ppm, and the water concentration is lower than 0.1 ppm.

6. The preparation method of the p-type CaMg2Sb2-based thermoelectric material according to claim 3, wherein, In step 3), a high-energy ball mill is used during ball milling, the rotation speed of the ball mill is 1500 r / min, and the ball milling time is 12 - 15 h.

7. The preparation method of the p-type CaMg2Sb2-based thermoelectric material according to claim 3, wherein In step 4), loading the powder into the graphite mold is completed in a glove box filled with argon.

8. The preparation method of the p-type CaMg2Sb2-based thermoelectric material according to claim 7, characterized in that, The oxygen concentration in the glove box is lower than 0.1 ppm, and the water concentration is lower than 0.1 ppm.

9. The preparation method of the p-type CaMg2Sb2-based thermoelectric material according to claim 3, wherein, In step 5), the spark plasma sintering process is as follows: Under the condition of lower than 20 Pa, first pressurize to 5 - 10 MPa; then heat up to 500 - 600 °C and pressurize to 50 - 70 MPa; subsequently, keep the pressure and temperature for 5 - 10 min, and carry out pressure reduction and temperature reduction after the pressure and temperature holding ends.

10. The preparation method of the p-type CaMg2Sb2-based thermoelectric material according to claim 9, characterized in that, All the pressurization rates are 5 - 10 MPa / min, and the heating rate is 50 - 100 °C / min.

Images