Method for rapidly preparing high-performance GeTe-based block thermoelectric material

Abstract

The invention relates to a method for rapidly preparing a high-performance GeTe-based block thermoelectric material. The method for rapidly preparing the GeTe-based block thermoelectric material comprises the following steps: firstly, weighing raw material powder elementary substance Ge powder, Te powder and Sb powder according to the stoichiometric ratio of GeTe or Ge0. 9Sb0. 1Te; then, in a high-purity argon gas environment, the raw material powder is placed in a ball milling tank to be refined and mixed; and finally, performing spark plasma sintering on the powder obtained by mixing in a vacuum environment at an extremely high temperature rise speed to form a solid thermal explosion reaction, so that the reaction and sintering are performed at the same time, the high-performance GeTe-based block thermoelectric material is obtained within 2 hours, and the dimensionless thermoelectric figure of merit zT at 750K can reach 1.8.

Description

Technical Field

[0001] The invention belongs to the technical field of energy materials, and in particular relates to a method for rapidly preparing a high-performance GeTe-based bulk thermoelectric material. Background Art

[0002] Thermoelectric conversion technology can realize the direct conversion of electrical energy and thermal energy. By adopting this technology, low-quality waste heat generated by garbage incineration, automobile exhaust, and industrial waste heat can be recovered and converted into electrical energy, thereby effectively improving energy utilization and alleviating the energy crisis. In addition, thermoelectric conversion technology can also achieve refrigeration and has important applications in the refrigeration of microelectronic equipment. Thermoelectric conversion technology is pollution-free, noise-free, and highly reliable, making it one of the most promising new energy technologies.

[0003] Narrow bandgap semiconductor GeTe-based thermoelectric materials are one of the most promising thermoelectric materials in the medium temperature range. GeTe undergoes a phase transition at around 700K, and at high temperatures it is a NaCl-type face-centered cubic crystal structure (space group is Fm-3m). As the temperature decreases, the atoms gradually move along the (111) diagonal direction, the overall angle of the unit cell deviates, and a phase transition occurs to a rhombohedral phase (space group is R3m). Under thermal equilibrium conditions, there are about 2% cation vacancies inside the GeTe lattice, so the GeTe material has an extremely high carrier concentration (10 21 cm -3 ).

[0004] In recent years, by introducing local resonance states, band degeneracy, dislocations, microstructure regulation and other methods, the zT value of GeTe-based materials has exceeded 2.0, making it a very promising medium-temperature thermoelectric material. However, up to now, GeTe-based thermoelectric materials have not been widely used in practice. This is because practical applications not only require high-performance thermoelectric materials, but also the material preparation process must be as energy-efficient and efficient as possible, suitable for large-scale commercial production. The current methods for preparing GeTe-based bulk thermoelectric materials mainly include melting method, mechanical alloying method, solid phase reaction method, etc. Their common feature is that the preparation of powders and densification sintering molding are divided into two or more steps. First, the single element is reacted at high temperature for a long time to synthesize the corresponding compound, then annealed for a long time to achieve uniform composition, and then the reaction product is crushed into a powder with uniform particles, and finally the powder is pressed into a dense block by SPS or hot pressing.

[0005] It can be seen that the traditional bulk thermoelectric material preparation method is complex and time-consuming, and cannot meet the needs of large-scale commercial production. Therefore, it is urgent to develop a method for quickly preparing high-performance GeTe-based bulk thermoelectric materials, so as to promote the application and development of GeTe-based thermoelectric materials in the medium temperature range. Summary of the invention

[0006] In view of the shortcomings of the above-mentioned existing preparation technology, the purpose of the present invention is to provide a method for quickly preparing high-performance GeTe-based bulk thermoelectric materials. The preparation method provided by the present invention shortens the entire preparation process from the traditional 5 days to less than 2 hours, and has the advantages of fast reaction speed, simple process, high efficiency and energy saving.

[0007] In a first aspect, the present invention provides a method for rapidly preparing a GeTe-based bulk thermoelectric material, the method comprising the following steps: First, according to GeTe or Ge 0.9 Sb 0.1 Weigh the raw material powders of Ge powder, Te powder and Sb powder in the stoichiometric ratio of Te; Then, the raw material powder is placed in a ball mill for ball milling and mixing under a high-purity argon environment; Finally, the powder obtained by ball milling is subjected to spark plasma sintering in a vacuum environment to obtain the GeTe-based bulk thermoelectric material.

[0008] Preferably, the purity of the raw material powders, Ge powder, Te powder and Sb powder, is ≥99.99%.

[0009] Preferably, the ball milling mixing method is planetary ball milling, the rotation speed of the ball mill is 450-500r / min, the ball-to-material ratio is 10-20:1, and a total of 2-4 cycles of ball milling are performed. The ball milling time of each cycle is 10-40min, and the stop time is 5-15min.

[0010] Preferably, the rotation speed of the ball mill is 500 r / min, the ball-to-material ratio is 15:1, and two cycles of ball milling are performed, with each cycle lasting 30 min and stopping for 15 min, for a total of 1.5 h.

[0011] Preferably, the particle size of the ball-milled mixed powder is 500 nm-1 μm.

[0012] Preferably, the spark plasma sintering pressure is 60-65 MPa, the sintering temperature is 423-723 K, the heating rate is 180-200 K / min, and the holding time is 5-10 min.

[0013] Preferably, the sintering pressure is 65 MPa, the heating rate is 200 K / min, and the heat preservation time is 10 min.

[0014] In a second aspect, the present invention provides a high-performance GeTe-based bulk thermoelectric material prepared according to the above method.

[0015] Preferably, the density of the GeTe-based bulk thermoelectric material is higher than 97%, and the maximum power factor is 28.52-40 μWcm-1 K -2 , the minimum thermal conductivity is 1.0-2.55Wm -1 K -1 , the dimensionless thermoelectric figure of merit zT can reach 1.8 at 750K.

[0016] Beneficial Effects (1) The present invention uses ball milling to refine and mix the raw material powders and then quickly discharge plasma sintering, which for the first time realizes the synthesis and densification process of GeTe-based bulk hotspot materials in one step. The entire preparation process is controlled within 2 hours. Compared with the traditional bulk thermoelectric material preparation method that takes more than 5 days, it has the advantages of fast reaction speed, simple process, high efficiency and energy saving; (2) The present invention greatly shortens the preparation cycle of GeTe-based bulk thermoelectric materials and abandons the preparation method of high-temperature melt annealing, thereby effectively reducing the volatilization of Te at high temperature and avoiding the introduction of more impurities in the long-cycle preparation process, and finally realizing the preparation of uniform pure-phase GeTe bulk materials; (3) The present invention refines and mixes the raw material powders by ball milling, and then uses spark plasma sintering to obtain GeTe-based bulk thermoelectric materials in a very short time. The prepared GeTe-based material is a uniform pure phase, and the thermoelectric figure of merit can reach 1.8 at 750K. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 XRD patterns of GeTe-based bulk thermoelectric material samples prepared in Examples 1-5; Figure 2 The scanning electron microscope backscattered electron image (BSE) and energy spectrum scanning image (EDS) of the GeTe-based bulk thermoelectric material sample prepared in Example 1; Figure 3 The graph is a relationship between the conductivity of the GeTe-based bulk thermoelectric material samples prepared in Examples 1-5 and Comparative Examples 1-2 and the temperature; Figure 4 is a graph showing the relationship between the Seebeck coefficient of the GeTe-based bulk thermoelectric material samples prepared in Examples 1-5 and Comparative Examples 1-2 and the temperature; Figure 5 It is a relationship diagram of the power factor PF of the GeTe-based bulk thermoelectric material samples prepared in Examples 1-5 and Comparative Examples 1-2 as a function of temperature; Figure 6 is a graph showing the relationship between the thermal conductivity of the GeTe-based bulk thermoelectric material samples prepared in Examples 1-5 and Comparative Examples 1-2 and the temperature; Figure 7 Graph showing the relationship between the thermoelectric figure of merit zT of the GeTe-based bulk thermoelectric material samples prepared in Examples 1-5 and Comparative Examples 1-2 and temperature. DETAILED DESCRIPTION

[0018] The present invention is further described below by the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, but not to limit the present invention.

[0019] First, the present invention provides a method for rapidly preparing a high-performance GeTe-based bulk thermoelectric material. The method may include the following steps: First, according to GeTe or Ge 0.9 Sb 0.1 Weigh the raw material powders of Ge powder, Te powder and Sb powder in the stoichiometric ratio of Te; Then, the raw material powder is placed in a ball mill for ball milling and mixing under a high-purity argon environment; Finally, the powder obtained by ball milling is subjected to spark plasma sintering in a vacuum environment to obtain the GeTe-based bulk thermoelectric material.

[0020] In some embodiments, the purity of the raw material powders, Ge powder, Te powder and Sb powder, is ≥99.99%.

[0021] In some embodiments, the ball milling mixing method can be planetary ball milling, the rotation speed of the ball mill can be 450-500r / min, the ball-to-material ratio can be 10-20:1, and a total of 2-4 cycles of ball milling are performed, the ball milling time for each cycle is 10-40min, and the stop time is 5-15min; preferably, the rotation speed of the ball mill is 500r / min, the ball-to-material ratio is 15:1, and a total of 2 cycles of ball milling are performed, the ball milling time for each cycle is 30min, and the stop time is 15min, for a total of 1.5h.

[0022] The main difference between the ball milling process provided by the present invention and the conventional ball milling process is that the rotation speed is relatively higher and the ball milling time is relatively shorter. Intermittent ball milling can avoid the continuous working time of the ball mill being too long, otherwise the heat generated in the case of high-speed ball milling is too large.

[0023] In some embodiments, the particle size of the mixed powder obtained by ball milling can be 500 nm to 1 μm.

[0024] The time and cycle of the ball milling process in the present invention are shortened because the ball milling process is not required to synthesize a single-phase compound, but to refine and mix the powder. Controlling the particle size of the powder is beneficial to the subsequent solid-state thermal explosion reaction through spark plasma sintering. If the particle size is too large, the thermal explosion reaction is difficult to complete quickly in a short time.

[0025] In some embodiments, the spark plasma sintering pressure can be 60-65MPa, the sintering temperature can be 423-723K, the heating rate can be 180-200K / min, and the insulation time can be 5-10min; preferably, the sintering pressure is 65MPa, the heating rate is 200K / min, and the insulation time is 10min.

[0026] The present invention controls the heating rate to quickly heat up in a short time, utilizes spark plasma sintering to realize solid-state thermal explosion reaction, thereby directly generating compounds in one step, and simultaneously realizing densification sintering; whereas the heating rate of conventional spark plasma sintering is generally slow, and the raw materials gradually react during the slow heating process, accompanied by a large number of intermediate products, which is a solid-state diffusion reaction and cannot directly generate single-phase compounds.

[0027] The GeTe-based bulk thermoelectric material prepared by the method provided by the present invention has a density higher than 97% and a maximum power factor of 28.52-40 μWcm -1 K -2 , the minimum thermal conductivity is 1.0-2.55Wm -1 K -1 , the dimensionless thermoelectric figure of merit zT can reach 1.8 at 750K.

[0028] The preparation method provided by the present invention first weighs high-purity Ge powder, Te powder and Sb powder according to the stoichiometric ratio, mixes them uniformly and refines the powder in a short time (such as 1.5 hours) by a planetary ball mill, and then performs spark plasma sintering on the mixed powder to directly prepare dense high-performance GeTe and Ge 0.9 Sb 0.1 Te bulk thermoelectric material has the advantages of fast reaction speed, simple process, high efficiency and energy saving. The entire preparation process can be shortened from more than 5 days of traditional high-temperature melting-annealing to less than 2 hours. The prepared GeTe-based material is a uniform pure phase, and the highest thermoelectric figure of merit can reach 1.8 at 750K.

[0029] The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values ​​​​exemplified below.

[0030] Example 1

[0031] The method for preparing the GeTe-based bulk thermoelectric material provided in this embodiment comprises the following steps: (1) First, weigh high-purity elemental raw materials Ge powder and Te powder according to the stoichiometric ratio of Ge:Te=1:1; (2) Then, the weighed single substance powder is placed in a glove box filled with high-purity argon gas and sealed in a ball mill for ball milling and mixing; wherein the ball milling and mixing method is planetary ball milling, the speed of the ball mill is 500 r / min, the ball-to-material ratio is 15:1, and a total of 2 ball milling cycles are performed, each cycle of ball milling time is 30 min, and the rest time is 15 min, for a total of 1.5 h; (3) Finally, the mixed powder with a particle size of 500 nm-1 μm obtained by ball milling is placed in a graphite mold with a diameter of 10 mm and spark plasma sintered in a vacuum environment with a sintering temperature of 723 K, a sintering pressure of 65 MPa, a heating rate of 200 K / min, and a holding time of 10 min to obtain a dense, high-performance GeTe-based bulk thermoelectric material.

[0032] Example 2

[0033] The preparation method of the GeTe-based bulk thermoelectric material provided in this embodiment refers to that in embodiment 1, the difference is that in step (1), high-purity single-substance raw materials Ge particles, Sb particles and Te particles are prepared according to Ge 0.9 Sb 0.1 The stoichiometric ratio of Te was weighed.

[0034] Example 3

[0035] The preparation method of the GeTe-based bulk thermoelectric material provided in this embodiment refers to that in Embodiment 2, except that the spark plasma sintering temperature in step (3) is 623K.

[0036] Example 4

[0037] The preparation method of the GeTe-based bulk thermoelectric material provided in this embodiment refers to that in Embodiment 2, except that the spark plasma sintering temperature in step (3) is 523K.

[0038] Example 5

[0039] The preparation method of the GeTe-based bulk thermoelectric material provided in this embodiment refers to that in Embodiment 2, except that the spark plasma sintering temperature in step (4) is 423K.

[0040] Comparative Example 1

[0041] The synthesis method of GeTe-based bulk thermoelectric materials in this comparative example refers to the literature (Tong Xing, et al. Ultralow lattice thermal conductivity and superhigh thermoelectric figure-of-merit in (Mg, Bi) co-doped GeTe, Advanced Materials, 2021, 33, 2008773). The specific preparation method includes the following steps: (1) Weigh high-purity elemental raw materials Ge and Te particles according to the stoichiometric ratio of Ge:Te=1:1; (2) The weighed single-element raw materials are mixed and sealed into a vacuum quartz tube, placed in a vertical melting furnace, and the furnace temperature is raised to 1373K over 11 hours, and kept warm for 12 hours. After sufficient reaction, the quartz tube is quickly placed in ice water for quenching; (3) placing the quenched quartz tube in an annealing furnace, heating it to 873K for 3 hours, annealing it for 5 days, and then cooling it to room temperature; (4) Grinding the annealed ingot into powder in a mortar, and then placing the powder into a graphite mold with a diameter of 10 mm for spark plasma sintering. The sintering is carried out in a vacuum environment at a sintering temperature of 823 K, a sintering pressure of 65 MPa, a heating rate of 100 K / min, and a holding time of 10 min. (5) Use an electric spark cutting machine to cut the obtained dense GeTe bulk sample for subsequent thermoelectric performance and structural characterization.

[0042] Comparative Example 2

[0043] The preparation method of the GeTe-based bulk thermoelectric material provided in this comparative example refers to comparative example 1, except that: in step (1), the high-purity single-substance raw materials Ge particles, Sb particles and Te particles are prepared according to Ge 0.9 Sb 0.1 The stoichiometric ratio of Te was weighed.

[0044] The structural characterization and thermoelectric performance test of the GeTe-based bulk thermoelectric materials prepared in Examples 1-5 and Comparative Examples 1-2 show that: The density of the GeTe-based bulk thermoelectric material sample prepared in Example 1 is 98.4%, and the maximum power factor is 39.63 μW cm -1 K -2 , the minimum thermal conductivity is 2.55Wm -1 K -1 , the dimensionless thermoelectric figure of merit zT is 1.2 at 750K; The density of the GeTe-based bulk thermoelectric material sample prepared in Example 2 is 99.2%, and the highest power factor is 39.63 μW cm -1 K -2 , the minimum thermal conductivity is 1.27Wm -1 K -1 , the dimensionless thermoelectric figure of merit zT is 1.8 at 750K; The density of the GeTe-based bulk thermoelectric material sample prepared in Example 3 is 98.8%, and the maximum power factor is 30.04 μW cm -1 K -2 , the minimum thermal conductivity is 1.64Wm -1 K -1 , the dimensionless thermoelectric figure of merit zT is 1.4 at 750K; The density of the GeTe-based bulk thermoelectric material sample prepared in Example 4 is 99.4%, and the maximum power factor is 30.62 μW cm -1 K -2 , the minimum thermal conductivity is 1.96Wm -1 K -1 , the dimensionless thermoelectric figure of merit zT is 1.2 at 750K; The density of the GeTe-based bulk thermoelectric material sample prepared in Example 5 is 97.8%, and the maximum power factor is 28.52 μW cm -1 K -2 , the minimum thermal conductivity is 2.26Wm -1 K -1 , the dimensionless thermoelectric figure of merit zT is 0.9 at 750K; The density of the GeTe-based bulk thermoelectric material sample prepared in Comparative Example 1 is 98.6%, and the highest power factor is 44.94 μW cm -1 K -2 , the minimum thermal conductivity is 2.49Wm -1 K -1 , the dimensionless thermoelectric figure of merit zT is 1.2 at 750K; The density of the GeTe-based bulk thermoelectric material sample prepared in Comparative Example 2 is 98.4%, and the highest power factor is 35.83 μW cm -1 K -2 , the minimum thermal conductivity is 1.41Wm -1 K -1 , the dimensionless thermoelectric figure of merit zT is 1.7 at 750K.

[0045] It can be seen that the embodiment of the present invention greatly shortens the preparation period compared with the comparative example, and still maintains excellent thermoelectric performance.

[0046] Figure 1XRD patterns of GeTe-based bulk thermoelectric material samples prepared in Examples 1-5. As can be seen from the figure, the rapid preparation method provided by the present invention can obtain high-purity GeTe and Ge 0.9 Sb 0.1 Te material.

[0047] Figure 2 The scanning electron microscope backscattered electron image (BSE) and energy spectrum scanning image (EDS) of the GeTe-based bulk thermoelectric material sample prepared in Example 1. It can be seen from the figure that the rapid preparation method provided by the present invention can obtain a pure-phase GeTe bulk material with uniform composition.

[0048] Figure 3 The relationship between the conductivity of the GeTe-based bulk thermoelectric material samples prepared in Examples 1-5 and Comparative Examples 1-2 and temperature changes is shown in the figure. It can be seen from the figure that the conductivity decreases with increasing temperature, and the conductivity of Example 1 is similar to that of Comparative Example 1, and the conductivity of Example 2 is similar to that of Comparative Example 2.

[0049] Figure 4 The relationship diagram of the Seebeck coefficient of the GeTe-based bulk thermoelectric material samples prepared in Examples 1-5 and Comparative Examples 1-2 as a function of temperature. It can be seen from the figure that the Seebeck coefficient increases with increasing temperature, and the Seebeck coefficients of Example 1 and Comparative Example 1 are similar, and the Seebeck coefficients of Example 2 and Comparative Example 2 are similar.

[0050] Figure 5 The figure is a relationship diagram of the power factor PF of the GeTe-based bulk thermoelectric material samples prepared in Examples 1-5 and Comparative Examples 1-2 as a function of temperature. It can be seen from the figure that below 600K, the material prepared in Example 2 has the highest power factor, and above 600K, the power factor of the material prepared in Example 2 decreases as the temperature increases.

[0051] Figure 6 The figure is a relationship diagram of the thermal conductivity of the GeTe-based bulk thermoelectric material samples prepared in Examples 1-5 and Comparative Examples 1-2 as a function of temperature. It can be seen from the figure that the thermal conductivity decreases with increasing temperature, and the thermal conductivity of Example 1 is similar to that of Comparative Example 1, and the thermal conductivity of Example 2 is similar to that of Comparative Example 2.

[0052] Figure 7 The figure is a relationship diagram of the thermoelectric figure of merit zT of the GeTe-based bulk thermoelectric material samples prepared in Examples 1-5 and Comparative Examples 1-2 as a function of temperature. As can be seen from the figure, the thermoelectric material prepared in Example 2 has the highest thermoelectric figure of merit zT, reaching 1.8 at 750K, which is relatively higher than the comparative example and other examples.

[0053] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for rapidly preparing GeTe-based bulk thermoelectric materials, characterized in that: The method comprises the following steps: First, according to GeTe or Ge 0.9 Sb 0.1 Weigh the raw material powders of Ge powder, Te powder and Sb powder in the stoichiometric ratio of Te; Then, the raw material powder is placed in a ball mill for ball milling and mixing under a high-purity argon environment; Finally, the powder obtained by ball milling is subjected to spark plasma sintering in a vacuum environment to obtain the GeTe-based bulk thermoelectric material.

2. The method according to claim 1, characterized in that The purity of the raw material powders, Ge powder, Te powder and Sb powder, is ≥99.99%.

3. The method according to claim 1 or 2, characterized in that: The ball milling mixing method is planetary ball milling, the rotation speed of the ball mill is 450-500r / min, the ball-to-material ratio is 10-20:1, and the ball milling is performed for 2-4 cycles. The ball milling time of each cycle is 10-40min, and the stop time is 5-15min.

4. The method according to any one of claims 1 to 3, characterized in that The rotation speed of the ball mill is 500 r / min, the ball-to-material ratio is 15:1, and there are 2 cycles of ball milling. The ball milling time of each cycle is 30 min, and the stop time is 15 min, for a total of 1.5 h.

5. The method according to any one of claims 1 to 4, characterized in that The particle size of the ball-milled mixed powder is 500nm-1μm.

6. The method according to any one of claims 1 to 5, characterized in that The spark plasma sintering pressure is 60-65 MPa, the sintering temperature is 423-723 K, the heating rate is 180-200 K / min, and the heat preservation time is 5-10 min.

7. The method according to any one of claims 1 to 6, characterized in that The sintering pressure is 65 MPa, the heating rate is 200 K / min, and the heat preservation time is 10 min.

8. A high-performance GeTe-based bulk thermoelectric material prepared according to the method of any one of claims 1-7.

9. The high performance GeTe-based bulk thermoelectric material according to claim 8, characterized in that: The high-performance GeTe-based bulk thermoelectric material has a density of more than 97% and a maximum power factor of 28.52-40 μW cm -1 K -2 , the minimum thermal conductivity is 1.0-2.55Wm -1 K -1 , the dimensionless thermoelectric figure of merit zT can reach 1.8 at 750K.

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