A large-size layered GeSb4Te7 single crystal and its preparation method

Abstract

The present invention belongs to the technical field of material preparation, and specifically relates to a large-sized layered GeSb4Te7 single crystal and a preparation method thereof. The method of the present invention comprises: (1) weighing raw material Ge particles, Sb particles and Te particles; (2) placing the raw material particles in a quartz crucible and evacuating the quartz crucible; (3) fixing the quartz crucible in the temperature gradient zone of the furnace of a vertical furnace, performing program temperature control, and obtaining a single crystal ingot; (4) adjusting the position of the quartz crucible containing the single crystal ingot to the upper and lower 3 cm area of ​​the vertical furnace thermocouple position for annealing, and then obtaining the large-sized layered GeSb4Te7 single crystal.

Description

Technical Field

[0001] The invention belongs to the technical field of material preparation, and in particular relates to a large-size layered GeSb4Te7 single crystal and a preparation method thereof. Background Art

[0002] Thermoelectric conversion technology can achieve direct mutual conversion between thermal energy and electrical energy without generating polluting emissions and noise in the process. Thermoelectric materials are expected to be applied to advanced solid-state devices to utilize residual thermal energy and convert it into electrical energy, thereby improving the overall utilization efficiency of fuel. GeSb4Te7 is a quasi-two-dimensional layered semiconductor with intrinsic low lattice conductivity, so it has high potential in thermoelectric applications. However, so far, the main research directions of GeSb4Te7-based thermoelectric materials have mostly focused on polycrystalline materials, and there are few reports on the thermoelectric properties of GeSb4Te7 single crystal materials.

[0003] The literature "Study on Thermoelectric Properties of GeSbTe-based Compounds with Quasi-Two-dimensional Structure" (University of Chinese Academy of Sciences, 202006) discloses a method for preparing GeSb4Te7 bulk samples using a melting-quenching-annealing process. This method places germanium (Ge, 99.999%), antimony (Sb, 99.999%) and tellurium (Te, 99.999%) into a vacuum quartz tube, and then places the quartz tube into a high-temperature furnace, and after heating-insulation-quenching treatment, a pure phase sample is obtained. The obtained sample is further ground into a powder of uniform coarseness and fineness, and then the powder is sintered and pressed into a dense block. It can be seen that the GeSb4Te7 prepared by this patent is a polycrystalline material.

[0004] The Bridgman method is a commonly used method for growing large-sized crystals. The traditional Bridgman method is also called the crucible descent method. This method is to control the furnace temperature of the equipment to be higher than the melting point of the compound during the crystal growth process, and then use the traction of the descending device to slowly descend the crucible from the high-temperature area of ​​the furnace to the low-temperature area to achieve slow crystallization of the melt, thereby growing a large-sized single crystal. However, during the process of the crucible descending, the external mechanical traction vibration often brings adverse effects, such as increased crystal defects, the formation of multi-nuclear growth during the spontaneous nucleation period, etc., which ultimately leads to a decrease in crystal quality.

[0005] In summary, in order to prepare large-sized, single-crystalline GeSb4Te7, it is necessary to propose new methods and strategies to improve the shortcomings of existing technologies. Summary of the invention

[0006] In view of this, the object of the present invention is to provide a large-sized layered GeSb4Te7 single crystal and a preparation method thereof, and the specific technical scheme is as follows.

[0007] A method for preparing a large-sized layered GeSb4Te7 single crystal, the preparation method is a cooling method, and the specific steps are as follows:

[0008] S01: weighing raw material Ge particles, Sb particles and Te particles, wherein the molar ratio of the Ge particles, Sb particles and Te particles is 19-21:77-83:137-143, and mixing the weighed raw material particles uniformly;

[0009] S02: placing the uniformly mixed raw material particles in a quartz crucible, and vacuum-sealing the quartz crucible;

[0010] S03: Fix the packaged quartz crucible in the temperature gradient zone of the furnace of the vertical furnace, at which time the distance between the tip of the quartz crucible and the bottom of the furnace is 6-12 cm, and set the temperature control program of the vertical furnace to increase the temperature to 900-1050° C. at a rate of 0.5-1.5° C. / min, so that the raw materials in the quartz crucible are in a molten state and maintained for 3-20 hours;

[0011] S04: adjusting the temperature control program of the vertical furnace to decrease to 700-850° C. at a rate of 0.5-5° C. / min;

[0012] S05: further adjusting the temperature control program of the vertical furnace to reduce the temperature to 500-600° C. at a rate of 0.5-2° C. / h, so that the material in the molten state in the quartz crucible completes crystallization (the material in the molten state gradually cools and turns into a solid, and the crystallization is determined to be completed when the temperature drops below the melting point), and obtaining a single crystal ingot;

[0013] S06: adjusting the position of the quartz crucible carrying the single crystal ingot to a position within 3 cm above and below the position of the thermocouple of the vertical furnace, and performing annealing treatment;

[0014] S07: Control the temperature of the vertical furnace to automatically cool down to room temperature to obtain the large-sized layered GeSb4Te7 single crystal.

[0015] In some preferred embodiments, the distance between the tip of the quartz crucible and the lowermost end of the furnace is 8 cm.

[0016] Furthermore, in S02, the quartz crucible is evacuated to a vacuum degree of less than or equal to 1 Pa.

[0017] Further, the temperature in S03 is raised to 900-1000°C at a rate of 0.5-1.5°C / min and maintained for 3-10h.

[0018] Furthermore, in S04, the temperature is reduced to 700-800°C at a rate of 0.5-1°C / min.

[0019] Furthermore, in S05, the temperature is reduced to 550-600°C at a rate of 1-2°C / h.

[0020] Furthermore, the annealing treatment in S06 is annealing at 300-500° C. for 4-8 hours.

[0021] Furthermore, in S05, the temperature is reduced to 580°C at a rate of 1-2°C / h.

[0022] Furthermore, in S04, the temperature is reduced to 800°C at a rate of 0.5-1°C / min.

[0023] The large-sized layered GeSb4Te7 single crystal prepared by the above preparation method.

[0024] The application of the above-mentioned large-sized layered GeSb4Te7 single crystal in the preparation of thermoelectric conversion electronic devices.

[0025] Beneficial technical effects

[0026] The present invention adopts the cooling method to successfully prepare a high-quality, large-size layered GeSb4Te7 single crystal. It is worth noting that there is no report on growing GeSb4Te7 single crystal using the cooling method used in the present invention.

[0027] The key points of the method of the present invention are that during the growth of a single crystal, the crucible is first fixed in a temperature gradient zone with a large temperature difference in the hearth of a vertical furnace, and the temperature of the hearth is slowly cooled by program control to achieve slow crystallization of the melt, thereby growing a large-sized single crystal ingot. After obtaining the single crystal ingot, the position of the crucible is further adjusted, and the crucible position is adjusted to a temperature gradient zone with a small hearth difference, that is, within a 3 cm area above and below the position of the thermocouple (the temperature in this area is relatively uniform) for annealing. The annealing operation can eliminate the defects inside the crystal as much as possible and release the residual stress inside the crystal, thereby finally obtaining a high-quality large-sized layered GeSb4Te7 single crystal. Therefore, the method of the present invention only needs to program the temperature of the single crystal furnace, and the operation is simpler. In addition, the method can also avoid the adverse effects caused by external mechanical traction vibration during the growth process of the traditional descending method, such as increased crystal defects, easy formation of multi-nuclear growth and development during the spontaneous nucleation period, etc., resulting in defects such as decreased crystal quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, each element or part is not necessarily drawn according to the actual scale. Obviously, the drawings described below are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without paying creative labor.

[0029] Figure 1 This is a schematic diagram of the structure of a vertical furnace used in an embodiment of the present invention;

[0030] Figure 2 This is a physical picture of the GeSb4Te7 single crystal ingot prepared in Example 2 of the present invention;

[0031] Figure 3 This is a physical picture of the GeSb4Te7 single crystal ingot prepared in Example 3 of the present invention;

[0032] Figure 4 This is a physical picture of the GeSb4Te7 single crystal ingot prepared in Example 4 of the present invention;

[0033] Figure 5 This is the X-ray diffraction pattern of the single crystal prepared in Example 2 of the present invention;

[0034] Figure 6 : A scanning electron microscope (SEM) image of a single crystal prepared in Example 2 of the present invention (a is the morphology of the cleavage plane of the single crystal, and b is the morphology of the cross section of the single crystal perpendicular to the cleavage plane);

[0035] Figure 7 The results of the phase and microstructure characterization of the single crystal prepared in Example 2 of the present invention are shown in Figure 1 (a is a scanning electron microscope-high angle annular dark field (STEM-HAADF) image, and b is an energy dispersive X-ray spectroscopy (EDX) spectrum);

[0036] Figure 8 This is a diagram showing the electrical performance test results of the single crystal prepared in Example 2 of the present invention (a is the temperature-dependent conductivity σ, and b is the Seebeck coefficient S). DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] Herein "and / or" includes any and all combinations of one or more of the associated listed items.

[0039] Herein, "plurality" means two or more than two, ie, it includes two, three, four, five, etc.

[0040] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0041] As used in this specification, the term "about" typically means + / - 5% of the stated value, more typically + / - 4% of the stated value, more typically + / - 3% of the stated value, more typically + / - 2% of the stated value, even more typically + / - 1% of the stated value, and even more typically + / - 0.5% of the stated value.

[0042] In this specification, some embodiments may be disclosed in a format of being within a certain range. It should be understood that such description of "being within a certain range" is only for convenience and brevity, and should not be interpreted as a rigid limitation on the disclosed range. Therefore, the description of the range should be considered to have specifically disclosed all possible sub-ranges and independent numerical values ​​within this range. For example, the range The description of should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within this range, for example, 1, 2, 3, 4, 5, and 6. The above rules apply regardless of the breadth of the range.

[0043] Example 1

[0044] This embodiment provides an example of a method for preparing large-sized layered GeSb4Te7 single crystals.

[0045] S01: Weigh raw material particles of Ge (99.999%), Sb (99.999%) and Te (99.99%) respectively according to the molar ratio of (19-21):(77-83):(137-143), mix them evenly, and obtain a raw material particle mixture.

[0046] S02: placing the raw material particle mixture into a quartz crucible, evacuating and sealing the quartz crucible until the vacuum degree is less than or equal to 1 Pa.

[0047] S03: Place the packaged quartz crucible in the temperature gradient zone of the furnace of the vertical furnace. At this time, the distance between the tip of the quartz crucible and the bottom of the furnace is 6-12 cm. Set the temperature control program of the vertical furnace to increase the temperature to 900-1050°C at a rate of 0.5-1.5°C / min, and keep the molten state at this temperature for 3-20 hours. The structural schematic diagram of the vertical furnace used in this embodiment is shown in Figure 1 . Figure 1 The temperature gradient of the furnace is divided into the first temperature gradient zone and the second temperature gradient zone. The first temperature gradient zone is relatively far from the thermocouple and closer to the lower end of the furnace, making it easier to exchange heat with the external environment and resulting in a larger temperature difference. In addition, when the heating element in the furnace is working, the hot air will rise, so the closer to the lower end of the furnace, the lower the temperature. The second temperature gradient zone is about 3 cm above and below the thermocouple position. This area is far away from the lower end of the furnace and has a relatively small temperature difference.

[0048] S04: Adjust the temperature control program of the vertical furnace so that the furnace temperature drops to 700-850°C at a rate of 0.5-5°C / min.

[0049] S05: Further adjust the temperature control program of the vertical furnace, and then slowly reduce the furnace temperature to 500-600°C at a rate of 0.5-2°C / h. After the melt slowly crystallizes, a GeSb4Te7 single crystal ingot is obtained.

[0050] S06: Raise the position of the quartz crucible containing the GeSb4Te7 single crystal ingot to within 3 cm above and below the position of the furnace thermocouple, and perform annealing treatment. The annealing time is 4-24 hours and the annealing temperature is 300-500°C.

[0051] S07: The furnace automatically cools down to room temperature, the crucible is taken out and cut open, and a conical GeSb4Te7 single crystal ingot is obtained.

[0052] Example 2

[0053] This embodiment provides a specific example of a method for preparing large-sized layered GeSb4Te7 single crystals. It can be understood that the method shown in this embodiment is only an example and not a limitation.

[0054] S01: Raw material particles of Ge (99.999%), Sb (99.999%) and Te (99.99%) were weighed respectively in a molar ratio of 20:80:140, and mixed evenly to obtain a raw material particle mixture.

[0055] S02: placing the raw material particle mixture into a quartz crucible, evacuating and sealing the quartz crucible until the vacuum degree is less than or equal to 1 Pa.

[0056] S03: placing the packaged quartz crucible in the temperature gradient zone of the furnace of a vertical furnace, where the distance between the tip of the quartz crucible and the bottom of the furnace is 8 cm, setting the temperature control program of the vertical furnace, heating to 1000°C at a rate of 1°C / min and maintaining the molten state at this temperature for 4 hours.

[0057] S04: Adjust the temperature control program of the vertical furnace and reduce the furnace temperature to 800°C at a rate of 0.5°C / min.

[0058] S05: Further adjust the temperature control program of the vertical furnace, slowly reduce the furnace temperature to 580°C at a rate of 1°C / h, and after the melt slowly crystallizes, obtain a GeSb4Te7 single crystal ingot.

[0059] S06: The position of the quartz crucible containing the GeSb4Te7 single crystal ingot is adjusted to be within the 5 cm area above and below the position of the furnace thermocouple for annealing. The annealing time is 4 hours and the annealing temperature is 500°C.

[0060] S07: The furnace automatically cools down to room temperature, the crucible is taken out and cut open, and a conical GeSb4Te7 single crystal ingot is obtained.

[0061] The actual picture of the conical GeSb4Te7 single crystal ingot prepared in this example is as follows Figure 2 The GeSb4Te7 single crystal ingot has a diameter of about 13 mm and a length of about 50 mm; its surface is smooth and has a metallic luster.

[0062] Example 3

[0063] This embodiment provides another specific example of a method for preparing large-sized layered GeSb4Te7 single crystals.

[0064] S01: Raw material particles of Ge (99.999%), Sb (99.999%) and Te (99.99%) were weighed respectively in a molar ratio of 20:80:140, and mixed evenly to obtain a raw material particle mixture.

[0065] S02: placing the raw material particle mixture into a quartz crucible, evacuating and sealing the quartz crucible until the vacuum degree is less than or equal to 1 Pa.

[0066] S03: placing the packaged quartz crucible in the temperature gradient zone of the furnace of a vertical furnace, where the distance between the tip of the quartz crucible and the bottom of the furnace is 10 cm, setting the temperature control program of the vertical furnace, heating to 1000°C at a rate of 1°C / min and maintaining the molten state at this temperature for 4 hours.

[0067] S04: Adjust the temperature control program of the vertical furnace and reduce the furnace temperature to 800°C at a rate of 1°C / min.

[0068] S05: Further adjust the temperature control program of the vertical furnace, slowly reduce the furnace temperature to 580°C at a rate of 1.5°C / h, and after the melt slowly crystallizes, obtain a GeSb4Te7 single crystal ingot.

[0069] S06: The position of the quartz crucible containing the GeSb4Te7 single crystal ingot is adjusted to the area 3 cm above and below the position of the furnace thermocouple for annealing. The annealing time is 4 hours and the annealing temperature is 450°C.

[0070] S07: The furnace automatically cools down to room temperature, the crucible is taken out and cut open, and a conical GeSb4Te7 single crystal ingot is obtained.

[0071] The actual picture of the conical GeSb4Te7 single crystal ingot prepared in this example is as follows Figure 3 The GeSb4Te7 single crystal ingot has a diameter of about 13 mm and a length of about 50 mm; its surface is relatively smooth and has a certain degree of metallic luster.

[0072] Example 4

[0073] This embodiment provides another specific example of a method for preparing large-sized layered GeSb4Te7 single crystals.

[0074] S01: Raw material particles of Ge (99.999%), Sb (99.999%) and Te (99.99%) were weighed respectively in a molar ratio of 20:80:140, and mixed evenly to obtain a raw material particle mixture.

[0075] S02: placing the raw material particle mixture into a quartz crucible, evacuating and sealing the quartz crucible until the vacuum degree is less than or equal to 1 Pa.

[0076] S03: Place the packaged quartz crucible in the temperature gradient zone of the furnace of a vertical furnace. At this time, the distance between the tip of the quartz crucible and the lower end of the furnace is 12 cm. Set the temperature control program of the vertical furnace to increase the temperature to 1000°C at a rate of 1°C / min and keep the molten state at this temperature for 4 hours.

[0077] S04: Adjust the temperature control program of the vertical furnace and reduce the furnace temperature to 800°C at a rate of 0.5°C / min.

[0078] S05: Further adjust the temperature control program of the vertical furnace, slowly reduce the furnace temperature to 580°C at a rate of 2°C / h, and after the melt slowly crystallizes, obtain a GeSb4Te7 single crystal ingot.

[0079] S06: The position of the quartz crucible containing the GeSb4Te7 single crystal ingot is adjusted to be within the 3 cm area above and below the position of the furnace thermocouple for annealing. The annealing time is 8 hours and the annealing temperature is 400°C.

[0080] S07: The furnace automatically cools down to room temperature, the crucible is taken out and cut open, and a conical GeSb4Te7 single crystal ingot is obtained.

[0081] The actual picture of the conical GeSb4Te7 single crystal ingot prepared in this example is as follows Figure 4 The GeSb4Te7 single crystal ingot has a diameter of about 13 mm and a length of about 50 mm; its surface is not smooth and has a dull metallic luster.

[0082] In summary, the temperature control program of the vertical furnace of the present invention is very important, including the cooling rate and cooling temperature of the present invention, as well as the position of the quartz crucible suspension. When these parameters are not well controlled, high-quality GeSb4Te7 single crystals cannot be obtained.

[0083] Example 5

[0084] This embodiment provides an example of another form of the method for preparing large-sized layered GeSb4Te7 single crystals.

[0085] S01: Raw material particles of Ge (99.999%), Sb (99.999%) and Te (99.99%) were weighed respectively according to the following molar ratios, and mixed evenly to obtain a raw material particle mixture.

[0086] Table 1 Comparison of different starting material ratios

[0087] Material molar ratio Ratio 1 Ratio 2 Ratio 3 Germanium (Ge) 19 20 21 Antimony (Sb) 77 81 83 Tellurium (Te) 137 139 143

[0088] S02: placing the raw material particle mixture into a quartz crucible, evacuating and sealing the quartz crucible until the vacuum degree is less than or equal to 1 Pa.

[0089] S03: placing the packaged quartz crucible in the temperature gradient zone of the furnace of a vertical furnace, where the distance between the tip of the quartz crucible and the bottom of the furnace is 8 cm, setting the temperature control program of the vertical furnace, heating to 1000°C at a rate of 1°C / min and maintaining the molten state at this temperature for 4 hours.

[0090] S04: Adjust the temperature control program of the vertical furnace and reduce the furnace temperature to 800°C at a rate of 0.5°C / min.

[0091] S05: Further adjust the temperature control program of the vertical furnace, slowly reduce the furnace temperature to 580°C at a rate of 1°C / h, and after the melt slowly crystallizes, obtain a GeSb4Te7 single crystal ingot.

[0092] S06: The position of the quartz crucible containing the GeSb4Te7 single crystal ingot is adjusted to be within the 3 cm area above and below the position of the furnace thermocouple for annealing. The annealing time is 4 hours and the annealing temperature is 500°C.

[0093] S07: The furnace automatically cools down to room temperature, the crucible is taken out and cut open, and a conical GeSb4Te7 single crystal ingot is obtained.

[0094] Example 6

[0095] This example provides the physical phase, microstructure characterization and electrical performance test of the GeSb4Te7 single crystal sample prepared in Example 2.

[0096] 6.1 The X-ray diffraction pattern of the GeSb4Te7 single crystal sample obtained in Example 2 was collected by X-ray diffractometer (see Figure 5 The cleavage surface morphology and cross-sectional morphology perpendicular to the cleavage surface of the GeSb4Te7 single crystal sample obtained in Example 2 were characterized by scanning electron microscopy (SEM-FIB, Thermoscientific Helios 5CX). The SEM image intuitively reflects the layered stacking characteristics of the single crystal sample (see Figure 6 ). Figure 7 The GeSb4Te7 single crystal sample obtained in Example 2 was characterized by scanning electron microscopy-high angle annular dark field (STEM-HAADF) and energy dispersive X-ray spectroscopy (EDX) using a transmission electron microscope (Spectra300). Figure 7 (a) shows that the 12 layers of atoms in the GeSb4Te7 single crystal sample are periodically arranged in a layered structure. Figure 7 (b) shows the uniform distribution of elements in the sample.

[0097] 6.2 The temperature-dependent conductivity σ and Seebeck coefficient S of the GeSb4Te7 single crystal sample obtained in Example 2 were simultaneously measured using an LSR-3 (Linseis, Germany) instrument, as shown in Table 6. Figure 8 (a) and (b), where Figure 8The illustration in (b) is a schematic diagram of processing single crystal electrical test samples in different directions (the direction perpendicular to the cleavage plane is c, and the direction parallel to the cleavage plane is a). In addition, the measurement errors of conductivity σ and Seebeck coefficient S are 5% and 7%, respectively.

[0098] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A method for preparing large-sized layered GeSb4Te7 single crystals, characterized in that: The preparation method is a cooling method, and the specific steps are as follows: S01: weighing raw material Ge particles, Sb particles and Te particles, wherein the molar ratio of the Ge particles, Sb particles and Te particles is 19-21:77-83:137-143, and mixing the weighed raw material particles uniformly; S02: placing the uniformly mixed raw material particles in a quartz crucible, and vacuum-sealing the quartz crucible; S03: Fix the packaged quartz crucible in the temperature gradient zone of the furnace of a vertical furnace, at which point the tip of the quartz crucible is 6-12 cm away from the bottom of the furnace, set the temperature control program of the vertical furnace, and raise the temperature to 900-1050° C. at a rate of 0.5-1.5° C. / min, so that the raw materials in the quartz crucible are in a molten state and maintained for 3-20 hours; S04: adjusting the temperature control program of the vertical furnace so that the temperature drops to 700-850° C. at a rate of 0.5-5° C. / min; S05: further adjusting the temperature control program of the vertical furnace to reduce the temperature to 500-600° C. at a rate of 0.5-2° C. / h, so that the molten material in the quartz crucible completes crystallization to obtain a single crystal ingot; S06: adjusting the position of the quartz crucible carrying the single crystal ingot to within the 3 cm area above and below the position of the thermocouple of the vertical furnace, and performing annealing treatment; the annealing treatment is annealing at 300-500° C. for 4-8 hours; S07: Control the temperature of the vertical furnace to automatically cool down to room temperature to obtain the large-sized layered GeSb4Te7 single crystal.

2. The preparation method according to claim 1, characterized in that In the step S02, the quartz crucible is evacuated to a vacuum degree of less than or equal to 1 Pa.

3. The preparation method according to claim 1, characterized in that: The S03 is heated to 900-1000°C at a rate of 0.5-1.5°C / min and maintained for 3-10h.

4. The preparation method according to claim 1, characterized in that: In S04, the temperature is reduced to 700-800°C at a rate of 0.5-1°C / min.

5. The preparation method according to claim 1, characterized in that: In S05, the temperature is reduced to 550-600°C at a rate of 1-2°C / h.

6. The preparation method according to claim 5, characterized in that: In S05, the temperature is lowered to 580°C at a rate of 1-2°C / h.

7. The preparation method according to claim 4, characterized in that: In S04, the temperature is reduced to 800°C at a rate of 0.5-1°C / min.

8. A large-sized layered GeSb4Te7 single crystal prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the large-sized layered GeSb4Te7 single crystal according to claim 8 in the preparation of thermoelectric conversion electronic devices.

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