A cubic phase germanium telluride-based thermoelectric material with high thermoelectric performance and mechanical performance and a preparation method thereof

Abstract

The application discloses a cubic germanium telluride-based thermoelectric material with high thermoelectric performance and mechanical performance and a preparation method thereof. 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. The application alloys GeTe with non-stoichiometric Ag 1‑δ Sb 1+δ Te 2+δ , and further dopes Cd and Pb elements. On one hand, the alloying and element doping significantly optimize the electric-thermal transport performance, so that the thermoelectric performance of the germanium telluride material is significantly improved. On the other hand, the doping of multiple elements increases the configurational entropy of the material, effectively improves the mechanical performance of the material, and is beneficial to the long-term service of the device. The preparation process of the thermoelectric material is simple, low in cost, good in repeatability and high in yield, and significantly improves the processing and use rate of the material.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric materials technology, specifically relating to a cubic phase germanium telluride-based thermoelectric material with both high thermoelectric and mechanical properties and its preparation method. Background Technology

[0002] Thermoelectric materials can directly achieve reversible, emission-free energy conversion between thermal and electrical energy. They are a new type of green energy material. Thermoelectric devices composed of these materials have advantages such as stable and reliable performance, no moving parts required for operation, and zero noise, making them widely applicable in fields such as solid-state cooling, thermoelectric power generation, and waste heat recovery. Thermoelectric performance is typically evaluated using the dimensionless thermoelectric figure of merit (ZT), calculated using the formula ZT = S. 2 As can be seen from σT / к, a good thermoelectric material must have a large Seebeck coefficient S and a high electrical conductivity σ, in addition to a low thermal conductivity к.

[0003] Germanium telluride (GeTe)-based thermoelectric materials, possessing excellent mechanical properties, are classic mid-temperature thermoelectric materials. However, GeTe undergoes a ferroelectric phase transition from a high-temperature cubic phase (C-GeTe) to a low-temperature rhombohedral phase (R-GeTe) at approximately 700 K. This ferroelectric phase transition causes the accumulation of significant strain and stress within the material, ultimately leading to fracture and severely hindering its lifespan and practical commercial applications. Therefore, the key to promoting the commercial application of GeTe-based thermoelectric materials lies in eliminating the ferroelectric phase transition to obtain a room-temperature cubic phase structure and improving the ZT value of the material. Studies by Ma et al. have shown that a non-stoichiometric Ag content dissolved in a GeTe matrix... 1-δ Sb 1+δ Te 2+δ Stable room-temperature cubic GeTe materials can be obtained with a δ value of 0.2–0.25 (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, their thermoelectric properties remain low, limiting the commercial application of GeTe-based materials. Therefore, developing cubic GeTe-based thermoelectric materials with high thermoelectric properties is of great practical significance. Summary of the Invention

[0004] In view of the problems existing in the prior art, the purpose of this invention is to provide a cubic phase germanium telluride-based thermoelectric material with high thermoelectric and mechanical properties, and to provide a simple, reproducible and low-cost preparation method for it.

[0005] To achieve the above objectives, the cubic germanium telluride-based thermoelectric material provided by this invention has the chemical formula 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, preferably x=0.02, y=0.04.

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

[0007] Step 1: According to Ge 0.614-x-y Cd x Pb y Ag 0.133 Sb 0.213 To determine the stoichiometric ratio of Te, weigh out individual elements of Ge, Cd, Pb, Ag, Sb, and Te, mix them thoroughly, and then place them into a quartz tube and seal it under vacuum.

[0008] Step 2: Place the quartz tube that was vacuum sealed in Step 1 into a muffle furnace, and quench the uniformly mixed elements after high-temperature melting.

[0009] Step 3: Place the quenched mixture from Step 2 into a muffle furnace for annealing to obtain the precursor ingot.

[0010] Step 4: Grind the precursor ingot from 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 step 1 above, the purity of the elemental Ge, Cd, Pb, Ag, Sb, and Te is all above 99.99%.

[0012] Furthermore, in step 1 above, the vacuum degree of the vacuum seal is ≤8×10⁻⁶. -4 Pa.

[0013] In step 2 above, the preferred high-temperature melting is to first hold at 400-450℃ for 2-4 hours, and then hold at 950-1050℃ for 12-18 hours, with a heating rate of 1-2℃ / min.

[0014] In step 3 above, the annealing temperature is preferably 500-550℃, the holding time is 24-30h, and the heating rate is 1-2℃ / min.

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

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] 1. This invention first introduces non-stoichiometric Ag into the GeTe matrix. 1-δ Sb 1+δ Te 2+δ A stable room-temperature cubic GeTe-based material was obtained with a doping density of δ = 0.23. Further doping with Cd and Pb resulted in severe lattice distortion due to differences in atomic size and mass among the multiple elements, promoting the formation of multi-scale microstructures and effectively enhancing phonon scattering, thereby reducing lattice thermal conductivity. Furthermore, Pb doping promoted valence band convergence, increasing the Seebeck coefficient and effectively improving the power factor. Combined with the reduced thermal conductivity, this significantly improved the thermoelectric performance of the material. On the other hand, the increased configurational entropy due to multi-element doping resulted in the germanium telluride-based thermoelectric material of this invention exhibiting excellent mechanical properties.

[0018] 2. The preparation method of the present invention has a simple process, low equipment requirements, and low cost. It only includes steps such as high-temperature melting, quenching, annealing, grinding, and sintering, which is conducive to large-scale production and application. Attached Figure Description

[0019] Figure 1 These are XRD patterns of the germanium telluride-based thermoelectric materials prepared in Examples 1-8 and Comparative Example 1.

[0020] Figure 2 The graphs (a) and (b) show the relationship between the conductivity and temperature of the germanium telluride-based thermoelectric materials prepared in Examples 1-8 and Comparative Example 1.

[0021] Figure 3 The graph shows the power factor of the germanium telluride-based thermoelectric materials prepared in Examples 1-8 and Comparative Example 1 as a function of temperature.

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

[0023] Figure 5The graph shows the thermoelectric figure of merit ZT of the germanium telluride-based thermoelectric materials prepared in Examples 1-8 and Comparative Example 1 as a function of temperature.

[0024] Figure 6 These are Vickers hardness diagrams of the germanium telluride-based thermoelectric materials prepared in Examples 1-8 and Comparative Example 1. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection 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 ratios of each element in Te were determined by weighing out individual elements of Ge, Cd, Ag, Sb, and Te with a purity of ≥99.99%. The weighed elements were then placed into a quartz tube and vacuum-sealed at a vacuum level of 7 × 10⁻⁶. -4 Pa.

[0028] Step 2: Transfer the vacuum-sealed quartz tube from Step 1 to a muffle furnace. First, heat it to 400℃ at a rate of 2℃ / min and hold for 2 hours. Then, heat it to 950℃ at a rate of 2℃ / min and hold for 12 hours. Finally, quench it.

[0029] Step 3: Transfer the quenched sealed quartz tube from Step 2 to a muffle furnace, heat it to 500℃ at a rate of 2℃ / min and hold it for 24 hours for annealing treatment, and then cool it to obtain the precursor ingot.

[0030] Step 4: After crushing and grinding the precursor ingot obtained in Step 3, room temperature cubic phase powder is obtained. The powder is then loaded into a mold for spark plasma sintering, wherein the sintering temperature is 450℃, the holding time is 5min, the sintering pressure is 50MPa, and the heating rate is 50℃ / 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 ratios of each element in Te were determined by weighing out elemental Ge, Cd, Ag, Sb, and Te with a purity of 99.99% or higher. The other steps were the same as in Example 1, resulting in germanium telluride-based thermoelectric materials.

[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 ratios of each element in Te were determined by weighing out elemental Ge, Cd, Ag, Sb, and Te with a purity of 99.99% or higher. The other steps were the same as in Example 1, resulting in germanium telluride-based thermoelectric materials.

[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 ratios of each element in Te were determined by weighing out elemental Ge, Cd, Ag, Sb, and Te with a purity of 99.99% or higher. The other steps were the same as in Example 1, resulting in germanium telluride-based thermoelectric materials.

[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 ratios of each element in Te were determined by weighing out elemental Ge, Cd, Pd, Ag, Sb, and Te with a purity of 99.99% or higher. The other steps were the same as in Example 1, resulting in germanium telluride-based thermoelectric materials.

[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 ratios of each element in Te were determined by weighing out elemental Ge, Cd, Pd, Ag, Sb, and Te with a purity of 99.99% or higher. The other steps were the same as in Example 1, resulting in germanium telluride-based thermoelectric materials.

[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 ratios of each element in Te were determined by weighing out elemental Ge, Cd, Pd, Ag, Sb, and Te with a purity of 99.99% or higher. The other steps were the same as in Example 1, resulting in germanium telluride-based thermoelectric materials.

[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 ratios of each element in Te were determined by weighing out elemental Ge, Cd, Pd, Ag, Sb, and Te with a purity of 99.99% or higher. The other steps were the same as in Example 1, resulting in germanium telluride-based thermoelectric materials.

[0045] Comparative Example 1

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

[0047] The thermoelectric materials obtained in the above embodiments and comparative examples were subjected to phase structure analysis using a MiniFlex 600 (Rigaku, Tokyo, Japan) X-ray diffractometer. The thermoelectric materials were then cut and polished with 2000-grit sandpaper. The conductivity and Seebeck coefficient of the samples were measured using a ZEM-3 (Ulvac-Riko, Japan) thermoelectric performance testing system, and the corresponding power factor PF = S was calculated. 2 σ. The method for calculating thermal conductivity is k = D × C. p ×ρ, where the thermal diffusivity D is measured using LFA 467 (Netzsch, Germany), and the specific heat C p The density ρ was calculated using the Dulong-Petit limit and measured using Archimedes' method of displacement. Finally, the formula ZT = S was used. 2 The thermoelectric figure of merit ZT of the sample was calculated using σT / к. The Vickers hardness tester was a Chinese HV-1000. The test results are shown below. Figures 1-6 .

[0048] By comparison Figure 1 The XRD patterns of the thermoelectric materials in Examples 1-8 and Comparative Example 1 show that the (003), (021), and (024) diffraction peaks in Examples 1-8 disappear, and the (111) and (220) diffraction peaks appear. This indicates that the thermoelectric materials described in this invention have a cubic phase crystal structure at room temperature, thus eliminating the ferroelectric phase transition at high temperatures.

[0049] By comparison Figure 2The electrical conductivity and Seebeck coefficient of the thermoelectric materials in Examples 1-8 and Comparative Example 1 change with temperature, and it can be found that the electrical conductivity decreases with increasing Cd and Pb doping concentration, while the Seebeck coefficient increases with increasing Cd and Pb doping concentration.

[0050] By comparison Figure 3 The relationship between the power factor of the thermoelectric materials in Examples 1-8 and Comparative Example 1 and the temperature shows that although the Seebeck coefficient of the thermoelectric materials in Examples 1-8 is effectively increased, it cannot compensate for the sharp decrease in conductivity, resulting in no increase in the maximum power factor. However, compared to Comparative Example 1, the power factor of the thermoelectric materials in Examples 1-8 is effectively improved across the entire temperature range of 323-623 K, with Example 6 showing a power factor of PF≈25.0 μW cm⁻¹ at room temperature. -1 K -2 This represents an increase of approximately 135.8% compared to control 1.

[0051] By comparison Figure 4 The relationship between the thermal conductivity of the thermoelectric materials in Examples 1-8 and Comparative Example 1 and the temperature shows that, due to the structural defects introduced by multi-element doping in the examples, which significantly enhance phonon scattering, the thermal conductivity of the thermoelectric materials in Examples 1-8 all decreased significantly in the temperature range of 323-773K.

[0052] Depend on Figure 5 As can be seen, the thermoelectric figure of merit ZT of the thermoelectric materials in Examples 1 to 8 is significantly improved. Among them, Example 6 obtained the maximum thermoelectric figure of merit ZT = 2.1, which is an improvement of about 130% compared with the maximum thermoelectric figure of merit ZT = 0.9 in Comparative Example 1.

[0053] By comparison Figure 6 The Vickers hardness of the thermoelectric materials in Examples 1-8 and Comparative Example 1 shows that the Vickers hardness of the thermoelectric materials in Examples 1-8 is improved compared to that of the thermoelectric material in Comparative Example 1. For example, the Vickers hardness of the thermoelectric material in Comparative Example 1 is 1.47 GPa, while the Vickers hardness of the thermoelectric material in Example 8 is 3.75 GPa, an increase of approximately 155%.

[0054] The present invention has been further described in detail through the above specific examples, but the present invention is not limited to the above embodiments. It should be noted that for those skilled in the art, simple substitutions or improvements made to the technical solutions of the present invention without departing from the concept of the present invention are all within the protection scope of the present invention.

Claims

1. A cubic germanium telluride-based thermoelectric material possessing both high thermoelectric and mechanical properties, characterized in that: The general 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, 0.02≤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 a cubic germanium telluride-based thermoelectric material with both high thermoelectric and mechanical properties as described in claim 1, characterized in that: The preparation method includes the following steps: Step 1: According to Ge 0.614-x-y Cd x Pb y Ag 0.133 Sb 0.213 To determine the stoichiometric ratio of Te, weigh out the elements Ge, Cd, Pb, Ag, Sb, and Te, mix them thoroughly, and then place them into a quartz tube and seal it under vacuum. Step 2: Place the vacuum-sealed quartz tube from Step 1 into a muffle furnace, and melt the uniformly mixed elements at high temperature and then quench them. The high-temperature melting is achieved by first holding the temperature at 400-450℃ for 2-4 hours, and then holding it at 950-1050℃ for 12-18 hours, with a heating rate of 1-2℃ / min. Step 3: Place the quenched mixture from Step 2 into a muffle furnace for annealing to obtain a precursor ingot; the annealing temperature is 500-550℃, the holding time is 24-30 h, and the heating rate is 1-2℃ / min. Step 4: After grinding the precursor ingot from Step 3 into powder, it is placed into a mold for sintering to obtain a dense bulk material, namely the germanium telluride-based thermoelectric material; the sintering is spark plasma sintering, the sintering temperature is 450-480℃, the holding time is 5-10 min, the sintering pressure is 40-50 MPa, and the heating rate is 50-100℃ / min.

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

5. The method for preparing the cubic germanium telluride-based thermoelectric material with both high thermoelectric and mechanical properties according to claim 3, characterized in that: In step 1, the vacuum degree of the vacuum seal is ≤8×10⁻⁶. -4 Pa.

Images