Cubic-phase germanium telluride-based thermoelectric material with high thermoelectric property and mechanical property and preparation method of cubic-phase germanium telluride-based thermoelectric material

Abstract

The invention discloses a cubic-phase germanium telluride-based thermoelectric material with both high thermoelectric performance and mechanical performance and a preparation method of the cubic-phase germanium telluride-based thermoelectric material. The chemical formula of the germanium telluride-based thermoelectric material is Ge < 0.614-x-y > Cd < x > Pb < y > Ag < 0.133 > Sb < 0.213 > Te, x is greater than or equal to 0.01 and less than or equal to 0.04, and y is greater than or equal to 0 and less than or equal to 0.08 According to the invention, GeTe and Ag < 1-delta > Sb < 1 + delta > Te < 2 + delta > in a non-stoichiometric ratio are alloyed, and Cd and Pb elements are further doped. On one hand, the electro-thermal transport performance is obviously optimized by alloying and element doping, so that the thermoelectric performance of the germanium telluride material is obviously improved. And on the other hand, due to multi-element doping, the configuration entropy of the material is increased, the mechanical property of the material is effectively improved, and long-term service of a device is facilitated. The thermoelectric material is simple in preparation process, low in cost, good in repeatability and high in yield, and the processing and utilization rate of the material is remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermoelectric materials, and specifically relates to a cubic germanium telluride-based thermoelectric material having both high thermoelectric performance and mechanical properties and a preparation method thereof. Background Art

[0002] Thermoelectric materials can directly realize reversible and emission-free energy conversion between thermal energy and electrical energy. It is a new type of green energy material. Thermoelectric devices composed of them have the advantages of stable and reliable performance, no moving parts in operation, and no noise, making them widely used in solid-state refrigeration, temperature difference power generation, waste heat recovery and other fields. The dimensionless thermoelectric figure of merit (ZT) is usually used to evaluate the thermoelectric performance of materials. According to its calculation formula ZT = S 2 From σT / к, we can see that a good thermoelectric material must have a large Seebeck coefficient S and a high electrical conductivity σ, and also a low thermal conductivity к.

[0003] Germanium telluride (GeTe)-based thermoelectric materials with good mechanical properties are classic medium-temperature thermoelectric materials, but GeTe undergoes a ferroelectric phase transition from a high-temperature cubic phase (C-GeTe) to a low-temperature rhombohedral phase (R-GeTe) at about 700K. This ferroelectric phase transition will cause a large amount of strain and stress to accumulate inside the material, eventually leading to the fracture of the material, which greatly hinders the service life of the material and its actual commercial application. Therefore, the key to promoting the commercial application of GeTe-based thermoelectric materials is to eliminate the ferroelectric phase transition to obtain a room temperature cubic phase structure and improve the ZT value of the material. Ma et al.'s study showed that by dissolving non-stoichiometric Ag in the GeTe matrix, the ZT value of the material can be increased. 1-δ Sb 1+δ Te 2+δ (δ=0.2~0.25) can obtain stable room temperature cubic phase GeTe materials (Baopeng Ma, Hongrui Ren, Fudong Zhang, Zhanhui Peng, Hailong He, Minchao Cui, Zhenhua Ge, Bingyu Li, Wenwen Wu, Pengfei Liang, Yu Xiao, Xiaolian Chao, Zupei Yang, and Di Wu, All cubic-phase δ-TAGS thermoelectrics over the entire mid-temperature range, Small 2023, 19, 2206439). However, its thermoelectric performance is still relatively low, which limits the commercial application of GeTe-based materials. Therefore, the development of cubic phase GeTe-based thermoelectric materials with high thermoelectric performance has great practical significance. Summary of the invention

[0004] In view of the problems existing in the prior art, the purpose of the present invention is to provide a cubic germanium telluride-based thermoelectric material with high thermoelectric and mechanical properties, and to provide a preparation method thereof with simple process, good repeatability and low cost.

[0005] For the above purpose, the cubic germanium telluride-based thermoelectric material provided by the present invention has the chemical formula Ge 0.614-x- y Cd x Pb y Ag 0.133 Sb 0.213 Te, wherein 0.01≤x≤0.04, 0≤y≤0.08, preferably x=0.02, y=0.04.

[0006] The preparation method of cubic germanium telluride-based thermoelectric material of the present invention comprises the following steps:

[0007] Step 1: Follow the Ge 0.614-x-y Cd x Pb y Ag 0.133 Sb 0.213 The stoichiometric ratio of Te is determined by weighing Ge, Cd, Pb, Ag, Sb, and Te respectively, mixing the weighed single substances evenly, putting them into a quartz tube, and vacuum sealing it.

[0008] Step 2: Place the quartz tube vacuum-sealed in step 1 in a muffle furnace to melt the uniformly mixed elements at high temperature and then quench them.

[0009] Step 3: placing the mixture quenched in step 2 in a muffle furnace for annealing to obtain a precursor ingot.

[0010] Step 4: Grind the precursor ingot obtained in step 3 into powder and then put it into a mold for sintering to obtain a dense bulk material, namely the germanium telluride-based thermoelectric material.

[0011] In the above step 1, the purity of the Ge, Cd, Pb, Ag, Sb and Te single substances is above 99.99%.

[0012] Furthermore, in the above step 1, the vacuum degree of the vacuum seal is ≤8×10 -4 Pa.

[0013] In the above step 2, preferably, the high temperature melting is firstly kept at 400-450°C for 2-4 hours, and then kept at 950-1050°C for 12-18 hours, with a heating rate of 1-2°C / min.

[0014] In the above step 3, it is preferred that the annealing treatment temperature is 500-550° C., the holding time is 24-30 h, and the heating rate is 1-2° C. / min.

[0015] In the above step 4, the sintering is preferably spark plasma sintering, the sintering temperature is 450-480° C., the holding time is 5-10 min, the sintering pressure is 40-50 MPa, and the heating rate is 50-100° C. / min.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. The present invention first introduces non-stoichiometric Ag into the GeTe matrix 1-δ Sb 1+δ Te 2+δ (δ=0.23) A stable room temperature cubic phase GeTe-based material is obtained. On this basis, Cd and Pb elements are further doped. Due to the atomic size and mass differences between multiple elements, a serious lattice distortion effect is caused, which promotes the formation of multi-scale microstructures and effectively enhances phonon scattering, thereby reducing lattice thermal conductivity. In addition, Pb doping promotes valence band convergence and increases the Seebeck coefficient, effectively improving the power factor, and greatly improving the thermoelectric performance of the material in combination with reduced thermal conductivity. On the other hand, since the doping of multiple elements increases the configuration entropy of the material, the germanium telluride-based thermoelectric material of the present invention has good mechanical properties.

[0018] 2. The preparation method of the present invention has a simple process, low equipment requirements and low cost. It only includes the steps of high-temperature melting, quenching, annealing, grinding, sintering, etc., which is conducive to large-scale production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 1 is the XRD diagram of the germanium telluride-based thermoelectric materials prepared in Examples 1 to 8 and Comparative Example 1.

[0020] Figure 2 1 is a graph showing the relationship between the conductivity of the germanium telluride-based thermoelectric materials prepared in Examples 1 to 8 and Comparative Example 1 and the temperature, and a graph showing the relationship between the Seebeck coefficient and the temperature, respectively.

[0021] Figure 3 3 is a graph showing the relationship between the power factor of the germanium telluride-based thermoelectric materials prepared in Examples 1 to 8 and Comparative Example 1 and the temperature.

[0022] Figure 4 3 is a graph showing the relationship between the thermal conductivity of the germanium telluride-based thermoelectric materials prepared in Examples 1 to 8 and Comparative Example 1 and the temperature.

[0023] Figure 5It is a graph showing the relationship between the thermoelectric figure of merit ZT of the germanium telluride-based thermoelectric materials prepared in Examples 1 to 8 and Comparative Example 1 and the change in temperature.

[0024] Figure 6 3 is a Vickers hardness diagram of germanium telluride-based thermoelectric materials prepared in Examples 1 to 8 and Comparative Example 1. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments, but the protection scope of the present invention is not limited to these embodiments.

[0026] Example 1

[0027] Step 1: According to the chemical formula Ge 0.604 Cd 0.01 Ag 0.133 Sb 0.213 The stoichiometric ratio of each element in Te is as follows: Ge, Cd, Ag, Sb, and Te with a purity of more than 99.99% are weighed respectively, and then all the weighed elements are placed in a quartz tube and vacuum-sealed, wherein the vacuum degree is 7×10 -4 Pa.

[0028] Step 2: Transfer the vacuum-sealed quartz tube in step 1 to a muffle furnace, first heat it to 400°C at a rate of 2°C / min and keep it for 2h, then heat it to 950°C at a rate of 2°C / min and keep it for 12h, and then quench it.

[0029] Step 3: Move the sealed quartz tube after quenching in step 2 to a muffle furnace, heat it to 500°C at a rate of 2°C / min and keep it for 24 hours for annealing, and obtain a precursor ingot after cooling.

[0030] Step 4: crush the precursor ingot obtained in step 3 and grind it to obtain room temperature cubic phase powder, and put the powder into a mold for spark plasma sintering, wherein the sintering temperature is 450°C, the holding time is 5 min, the sintering pressure is 50 MPa, and the heating rate is 50°C / min to obtain germanium telluride-based thermoelectric material.

[0031] Example 2

[0032] In step 1 of this embodiment, according to the chemical formula Ge 0.594 Cd 0.02 Ag 0.133 Sb 0.213 The stoichiometric ratio of each element in Te is as follows: Ge, Cd, Ag, Sb, and Te single substances with a purity of more than 99.99% are weighed respectively, and the other steps are the same as those in Example 1 to obtain a germanium telluride-based thermoelectric material.

[0033] Example 3

[0034] In step 1 of this embodiment, according to the chemical formula Ge 0.584 Cd 0.03 Ag 0.133 Sb 0.213 The stoichiometric ratio of each element in Te is as follows: Ge, Cd, Ag, Sb, and Te single substances with a purity of more than 99.99% are weighed respectively, and the other steps are the same as those in Example 1 to obtain a germanium telluride-based thermoelectric material.

[0035] Example 4

[0036] In step 1 of this embodiment, according to the chemical formula Ge 0.574 Cd 0.04 Ag 0.133 Sb 0.213 The stoichiometric ratio of each element in Te is as follows: Ge, Cd, Ag, Sb, and Te single substances with a purity of more than 99.99% are weighed respectively, and the other steps are the same as those in Example 1 to obtain a germanium telluride-based thermoelectric material.

[0037] Example 5

[0038] In step 1 of this embodiment, according to the chemical formula Ge 0.574 Cd 0.02 Pb 0.02 Ag 0.133 Sb 0.213 The stoichiometric ratio of each element in Te is respectively weighed as Ge, Cd, Pd, Ag, Sb, and Te single substances with a purity of more than 99.99%, and the other steps are the same as those in Example 1 to obtain a germanium telluride-based thermoelectric material.

[0039] Example 6

[0040] In step 1 of this embodiment, according to the chemical formula Ge 0.554 Cd 0.02 Pb 0.04 Ag 0.133 Sb 0.213 The stoichiometric ratio of each element in Te is respectively weighed as Ge, Cd, Pd, Ag, Sb, and Te single substances with a purity of more than 99.99%, and the other steps are the same as those in Example 1 to obtain a germanium telluride-based thermoelectric material.

[0041] Example 7

[0042] In step 1 of this embodiment, according to the chemical formula Ge 0.534 Cd 0.02 Pb 0.06 Ag 0.133 Sb 0.213 The stoichiometric ratio of each element in Te is respectively weighed as Ge, Cd, Pd, Ag, Sb, and Te single substances with a purity of more than 99.99%, and the other steps are the same as those in Example 1 to obtain a germanium telluride-based thermoelectric material.

[0043] Example 8

[0044] In step 1 of this embodiment, according to the chemical formula Ge 0.514 Cd 0.02 Pb 0.08 Ag 0.133 Sb 0.213 The stoichiometric ratio of each element in Te is respectively weighed as Ge, Cd, Pd, Ag, Sb, and Te single substances with a purity of more than 99.99%, and the other steps are the same as those in Example 1 to obtain a germanium telluride-based thermoelectric material.

[0045] Comparative Example 1

[0046] In this comparative example, Ge and Te single substances with a purity of more than 99.99% were weighed according to the stoichiometric ratio of each element in the chemical formula GeTe, and no quenching and annealing treatment was required. The other steps were the same as in Example 1 to obtain germanium telluride thermoelectric material.

[0047] The thermoelectric materials obtained in the above examples and comparative examples were analyzed for phase structure using a MiniFlex600 (Rigaku, Tokyo, Japan) X-ray diffractometer. The thermoelectric materials were then cut and polished with 2000-grit sandpaper. The ZEM-3 (Ulvac-Riko, Japan) thermoelectric performance test system was used to measure the conductivity and Seebeck coefficient of the samples, and the corresponding power factor PF=S was calculated. 2 σ. The calculation method of thermal conductivity is k = D × C p ×ρ, where the thermal diffusion coefficient D is measured by LFA 467 (Netzsch, Germany), and the specific heat C p The density ρ is calculated by the Dulong-Petit limit and measured by the Archimedean drainage method. Finally, the formula ZT=S 2 The thermoelectric figure of merit ZT of the sample is calculated by σT / к. The Vickers hardness tester is China HV-1000. The test results are shown in Figures 1 to 6 .

[0048] By comparison Figure 1 From the XRD patterns of the thermoelectric materials of Examples 1 to 8 and Comparative Example 1, it can be found that the (003), (021), and (024) diffraction peaks in Examples 1 to 8 disappear, and (111) and (220) diffraction peaks appear, indicating that the thermoelectric materials of the present invention have a cubic phase crystal structure at room temperature, eliminating the ferroelectric phase transition at high temperature.

[0049] By comparison Figure 2From the relationship between the temperature variation of the electrical conductivity and the temperature variation of the electrical Seebeck coefficient of the thermoelectric materials in Examples 1 to 8 and Comparative Example 1, it can be found that as the Cd and Pb doping amounts increase, the electrical conductivity decreases, while the Seebeck coefficient has the opposite trend, increasing as the Cd and Pb doping amounts increase.

[0050] By comparison Figure 3 The relationship between the power factor of the thermoelectric materials of Examples 1 to 8 and Comparative Example 1 and the change in temperature shows that although the Seebeck coefficient of the thermoelectric materials of Examples 1 to 8 is effectively increased, it cannot make up for the sharp decrease in conductivity, resulting in no increase in the maximum value of the power factor. However, compared with Comparative Example 1, the power factor of the thermoelectric materials of Examples 1 to 8 is effectively improved in the entire temperature range of 323 to 623 K, among which the room temperature PF of Example 6 is ≈ 25.0 μW cm -1 K -2 , which is about 135.8% higher than that of Comparative Example 1.

[0051] By comparison Figure 4 From the relationship between the thermal conductivity of the thermoelectric materials in Examples 1 to 8 and Comparative Example 1 and the temperature, it can be found that since the structural defects introduced by multi-element doping in the examples significantly enhanced phonon scattering, the thermal conductivity of the thermoelectric materials in Examples 1 to 8 decreased significantly in the temperature range of 323 to 773 K.

[0052] Depend on Figure 5 It can be seen that the thermoelectric figures of merit ZT of the thermoelectric materials of Examples 1 to 8 are all significantly improved. Among them, Example 6 obtains a maximum thermoelectric figure of merit ZT=2.1, which is about 130% higher than the maximum thermoelectric figure of merit ZT=0.9 of Comparative Example 1.

[0053] By comparison Figure 6 It can be found from the Vickers hardness of the thermoelectric materials of Examples 1 to 8 and Comparative Example 1 that the Vickers hardness of the thermoelectric materials of Examples 1 to 8 is improved compared with that of the thermoelectric material of Comparative Example 1. For example, the Vickers hardness of the thermoelectric material of Comparative Example 1 is 1.47 GPa, and the Vickers hardness of the thermoelectric material of Example 8 is 3.75 GPa, which is improved by about 155%.

[0054] The present invention further describes the preferred embodiments of the present invention in detail through the above specific examples, but the present invention is not limited to the above embodiments. It should be pointed out that for ordinary technicians in the technical field of the present invention, without departing from the concept of the present invention, simple replacement or improvement of the technical solution of the present invention is made, which all belong to the protection scope of the present invention.

Claims

1. A cubic germanium telluride-based thermoelectric material having both high thermoelectric performance and mechanical properties, characterized in that: The chemical formula of the thermoelectric material is Ge 0.614-x-y Cd x Pb y Ag 0.133 Sb 0.213 Te, where 0.01≤x≤0.04, 0≤y≤0.

08.

2. The cubic germanium telluride-based thermoelectric material with high thermoelectric and mechanical properties according to claim 1, characterized in that: x=0.02, y=0.

04.

3. A method for preparing the cubic germanium telluride-based thermoelectric material having both high thermoelectric performance and mechanical properties as claimed in claim 1, characterized in that: The preparation method comprises the following steps: Step 1: Follow the Ge 0.614-x-y Cd x Pb y Ag 0.133 Sb 0.213 The stoichiometric ratio of Te is determined by weighing Ge, Cd, Pb, Ag, Sb, and Te respectively, mixing the weighed single substances evenly, and then putting them into a quartz tube, which is vacuum-sealed; Step 2: placing the quartz tube vacuum-sealed in step 1 in a muffle furnace, melting the uniformly mixed single substances at high temperature and then quenching; Step 3: placing the mixture quenched in step 2 in a muffle furnace for annealing to obtain a precursor ingot; Step 4: Grind the precursor ingot obtained in step 3 into powder and then put it into a mold for sintering to obtain a dense bulk material, namely the germanium telluride-based thermoelectric material.

4. The method for preparing a cubic germanium telluride-based thermoelectric material having both high thermoelectric performance and mechanical properties according to claim 3, characterized in that: In step 1, the purity of the Ge, Cd, Pb, Ag, Sb and Te single substances is above 99.99%.

5. The method for preparing a cubic germanium telluride-based thermoelectric material having both high thermoelectric performance and mechanical properties according to claim 3, characterized in that: In step 1, the vacuum degree of the vacuum seal is ≤8×10 -4 Pa.

6. The method for preparing a cubic germanium telluride-based thermoelectric material having both high thermoelectric performance and mechanical properties according to claim 3, characterized in that: In step 2, the high temperature melting is firstly kept at 400-450°C for 2-4 hours, and then kept at 950-1050°C for 12-18 hours, with a heating rate of 1-2°C / min.

7. The method for preparing a cubic germanium telluride-based thermoelectric material having both high thermoelectric performance and mechanical properties according to claim 3, characterized in that: In step 3, the annealing treatment temperature is 500-550° C., the holding time is 24-30 hours, and the heating rate is 1-2° C. / min.

8. The method for preparing a cubic germanium telluride-based thermoelectric material having both high thermoelectric performance and mechanical properties according to claim 3, characterized in that: In step 4, the sintering is spark plasma sintering, the sintering temperature is 450-480° C., the holding time is 5-10 min, the sintering pressure is 40-50 MPa, and the heating rate is 50-100° C. / min.

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