GeTe single crystal and preparation method and application thereof

Abstract

The invention belongs to the field of material preparation, and particularly relates to a GeTe single crystal and a preparation method and application thereof. The invention provides a GeTe single crystal and a vapor deposition preparation method thereof in order to solve the technical problem of Ge precipitation generally existing in a GeTe-based material prepared by a traditional melting method. The chemical formula of the GeTe single crystal is Ge < 1-x > M < x > Te; wherein M comprises at least one of Sb and Bi, and x is more than or equal to 0 and less than or equal to 0.1; preferably, the size of the GeTe single crystal ranges from 2 mm to 6 mm. The size of the GeTe single crystal prepared by the method can reach 2-6mm, and the GeTe single crystal has regular morphology, good crystallization and high quality.

Description

Technical Field

[0001] The present invention belongs to the field of material preparation, and in particular relates to a GeTe single crystal and a preparation method thereof, as well as applications in the field of thermoelectric materials. Background Art

[0002] Thermoelectric conversion is an environmentally friendly energy conversion technology based on the Seebeck and Peltier effects, enabling direct conversion of heat into electricity. This technology is all-solid-state, noiseless, and emission-free, and has applications in deep space exploration, waste heat recovery, and small-scale refrigeration.

[0003] The performance of thermoelectric materials is usually described by the dimensionless thermoelectric figure of merit (zT), which is defined as zT = σS 2 T / κ, where σ, S, κ and T are the electrical conductivity, Seebeck coefficient, thermal conductivity and absolute temperature of the material, respectively. It can be seen that thermoelectric materials with excellent performance should have both good electrical transport properties and low thermal conductivity.

[0004] Germanium telluride (GeTe) is one of the most popular thermoelectric materials in recent years, with high electrical transport performance. GeTe bulk materials are usually prepared by melt-spark plasma sintering / hot pressing sintering process. The zT max By doping heterovalent elements (Sb / Bi) at the Ge site to optimize the carrier concentration, the electrical and thermal conductivity of GeTe-based materials are reduced, and the Seebeck coefficient is significantly improved, zT max It can reach about 1.8. On the basis of optimizing the carrier concentration, the introduction of phonon scattering structures such as multi-scale defects can reduce the lattice thermal conductivity of GeTe-based materials, making its zT max Reach 2.0 or above.

[0005] Regarding the stability of GeTe-based materials, current research focuses on the regulation of phase transition and mechanical properties. GeTe materials undergo a phase transition around 700K, from a low-temperature rhombohedral phase (space group R3m, hereinafter referred to as R-GeTe) to a high-temperature cubic phase (space group During the phase transition (hereinafter referred to as C-GeTe), the volume shrinks significantly and the thermal expansion coefficient undergoes a sudden change. This can lead to significant stress within thermoelectric materials operating under temperature differences, affecting the service life of thermoelectric devices. Previous studies have shown that doping with elements such as Mg and Mn can effectively adjust the crystal structure and mechanical strength of GeTe-based materials, thereby reducing the volume change during the phase transition. However, the mechanism that alters the stability of GeTe-based materials is still unclear, making it difficult to precisely control the relevant properties.

[0006] It is worth noting that GeTe-based materials prepared by traditional melt methods commonly exhibit Ge precipitation, effectively forming composite materials of GeTe and Ge. The impact of the Ge second phase on the thermoelectric transport and mechanical properties of these materials is unknown. Furthermore, the preparation of GeTe bulk single crystals is rarely reported, and the preparation of GeTe single crystal samples is crucial for studying their intrinsic thermoelectric transport behavior and phase transition mechanisms. Summary of the Invention

[0007] To solve the problems of the prior art, the present invention provides a GeTe single crystal and a method for preparing the same by vapor deposition. The GeTe single crystal prepared by the present invention does not have Ge precipitation and can be used to study the intrinsic properties and phase transition mechanism of GeTe-based materials. It can also be used to sinter and prepare high-purity GeTe-based bulk materials.

[0008] In one aspect, the present invention provides a GeTe single crystal, wherein the chemical formula of the GeTe single crystal is Ge 1-x M x Te; wherein M includes at least one of Sb and Bi, 0≤x≤0.1; preferably, the size of the GeTe single crystal is 2 to 6 mm.

[0009] Preferably, 0<x≤0.1.

[0010] In another aspect, the present invention provides a method for preparing a GeTe single crystal, comprising: (1) Selecting GeTe-based polycrystalline material as raw material, placing it in a clean quartz tube and vacuum sealing it; (2) placing the vacuum-sealed quartz tube horizontally into a holding furnace to perform a vapor deposition reaction of GeTe, so that a GeTe single crystal is deposited and grown on the inner wall of the quartz tube; (3) The deposited product on the inner wall of the quartz tube is taken out, and then cleaned and dried to obtain the GeTe single crystal.

[0011] Preferably, the GeTe-based polycrystalline material is in bulk or powder form.

[0012] Preferably, when the quartz tube is vacuum sealed, the gas pressure in the quartz tube is controlled to be less than 6 Pa, and argon gas is used for three times of purge.

[0013] Preferably, the inner wall of the quartz tube is first carbonized. The carbonization process parameters include: spraying a carbon source onto a portion of the inner wall of the quartz tube, followed by carbonization; the carbon source is at least one of alcohol and acetone; and the carbonization temperature is 1500-1600°C. Carbonization of the inner wall of the quartz tube can reduce the number of deposition sites for GeTe-based materials, lowering the probability of GeTe single crystal nucleation, thereby promoting single crystal growth and yielding fewer and larger GeTe single crystals under the same reaction conditions.

[0014] Preferably, the parameters of the vapor deposition reaction include: the heating temperature of the quartz tube is 600-650° C.; the insulation time of the quartz tube is 2-4 days; and the heating rate of the quartz tube is 100-200° C. / h.

[0015] Preferably, the cleaning method is ultrasonic cleaning; the number of ultrasonic cleaning is no less than 3 times, and each time lasts for 10 to 15 minutes.

[0016] In another aspect, the present invention provides an application of GeTe single crystal in the field of thermoelectric materials.

[0017] Beneficial effects of the present invention: The present invention provides a method for preparing GeTe single crystals. The method has the advantages of simple operation and low cost. The prepared GeTe single crystals can reach a size of 2 to 6 mm, have regular morphology, good crystallization, and high quality. The GeTe single crystal prepared by the present invention can be used to carry out research on the intrinsic structure and thermoelectric transport performance of GeTe, and can be used to prepare high-purity GeTe bulk materials, solving the problem of Ge second phase precipitation in the existing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the device for preparing GeTe single crystals by vapor deposition; Figure 2 are the condition parameters of the vapor deposition reaction in Example 4 and Comparative Example 1; Figure 3 These are photos of GeTe single crystals prepared by vapor deposition in Example 4 and Comparative Example 1; Figure 4 is the X-ray diffraction pattern of the (202) crystal plane of the GeTe single crystal prepared by vapor deposition in Example 1; Figure 5 is the powder X-ray diffraction pattern of the GeTe single crystal prepared by vapor deposition in Example 1; Figure 6 The scanning electron microscope image and element distribution map of the GeTe single crystal prepared by vapor deposition in Example 1; Figure 7 The Ge prepared by vapor deposition in Example 5 0.9 Sb 0.1 Powder X-ray diffraction pattern of Te single crystal; Figure 8 The Ge prepared by vapor deposition in Example 5 0.9 Sb 0.1 Scanning electron microscope image and element distribution map of Te single crystal; DETAILED DESCRIPTION

[0019] The present invention is further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, rather than to limit the present invention.

[0020] In the present invention, the chemical formula of the GeTe single crystal provided is Ge 1-x M x Te, wherein the value range of x is 0≤x≤0.1, and M includes but is not limited to doping elements such as Sb and Bi.

[0021] In the present invention, GeTe-based materials are used as raw materials, vacuum-encapsulated in a quartz tube, and GeTe single crystals are vapor-deposited and grown at 600-650° C. The following is an exemplary description of the preparation method of GeTe single crystals.

[0022] Raw material preparation: Based on the value of x in the chemical formula of the target GeTe single crystal, select the corresponding GeTe-based polycrystalline material as the raw material. Place the raw material into a clean quartz tube, seal it with a vacuum sealer, and set aside. The GeTe-based polycrystalline material can be in bulk or powder form, and its synthesis methods include but are not limited to traditional melting and ball milling. During vacuum sealing, the pressure inside the quartz tube must be less than 6 Pa, and the tube must be purged three times with argon gas.

[0023] In an optional embodiment, the inner wall of the quartz tube is carbon-plated to reduce the deposition sites of GeTe-based materials and reduce the nucleation probability of GeTe single crystals, thereby promoting the growth of single crystals and obtaining fewer and larger GeTe single crystals under the same reaction conditions. The specific operation of carbon plating is: first, use a small amount of alcohol to wet the surface of the inner wall of the quartz tube, and then use the high temperature (about 1600°C) inner flame of a gas oxygen flame gun to heat the outer wall of the quartz tube to carbonize the alcohol on the inner wall to form a carbon layer. It should be noted that the GeTe single crystal will not be able to nucleate at the carbon-plated position, so the inner wall of the quartz tube needs to retain at least one uncarbon-plated area to provide a nucleation site.

[0024] Vapor deposition: Place the prepared quartz tube horizontally into a holding furnace to perform a vapor deposition reaction of GeTe, causing GeTe single crystals to deposit and grow on the inner wall of the quartz tube. Specifically, heat the quartz tube containing the raw materials to 600-650°C at a rate of 100-200°C / h and hold it for 2-4 days. Preferably, heat the quartz tube containing the raw materials to 650°C at a rate of 200°C / h and hold it for 3 days.

[0025] Ultrasonic cleaning: Remove the deposited product from the inner wall of the quartz tube, select the regularly shaped, intact crystals, and perform ultrasonic cleaning using ethanol to remove surface contaminants. After cleaning, air dry the crystals to obtain GeTe single crystals. Perform ultrasonic cleaning at least three times, each lasting 10–15 minutes.

[0026] In the present invention, the obtained GeTe single crystal has a size of 2 to 6 mm, regular morphology, good crystallization and high quality, and can be used to carry out research on the intrinsic structure and thermoelectric transport properties of GeTe-based materials, and can also be used for sintering to prepare high-purity GeTe-based bulk materials.

[0027] The following examples are further 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 all fall within the scope of protection of the present invention. The specific process parameters and the like in the following examples are only examples within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description herein, and are not limited to the specific numerical values ​​exemplified below.

[0028] Example 1: A method for preparing a GeTe single crystal comprises the following steps: S1. Raw material preparation: Weigh approximately 1 g of bulk GeTe polycrystalline material prepared by the melt method as the reaction raw material and place it into a clean quartz tube. Evacuate the tube using a vacuum sealer until the pressure inside the tube drops to 6 Pa. Purge the tube three times with argon gas, then vacuum seal and set aside. S2. Vapor deposition: The quartz tube prepared in step S1 is placed horizontally in a holding furnace, and the quartz tube containing the raw materials is heated to 600°C at a rate of 200°C / h and kept at this temperature for 3 days to perform a vapor deposition reaction of GeTe, so that a GeTe single crystal is deposited and grown on the inner wall of the quartz tube; S3. Ultrasonic Cleaning: Remove the deposited product from step S2 on the inner wall of the quartz tube, select the regularly shaped, intact crystals, and perform three ultrasonic cleanings using ethanol, each lasting 15 minutes, to remove surface contaminants. After cleaning, air-dry the tube to obtain a GeTe single crystal. The resulting GeTe single crystal is approximately 2 mm in size.

[0029] Example 2: A method for preparing a GeTe single crystal comprises the following steps: S1. Raw material preparation: This step is the same as in Example 1; S2. Vapor deposition: The quartz tube prepared in step S1 is placed horizontally in a holding furnace, and the quartz tube containing the raw materials is heated to 650°C at a rate of 200°C / h and kept at this temperature for 3 days to perform a vapor deposition reaction of GeTe, so that a GeTe single crystal is deposited and grown on the inner wall of the quartz tube; S3. Ultrasonic cleaning: This step is the same as in Example 1. The size of the obtained GeTe single crystal is 3-4 mm, indicating that increasing the temperature can accelerate the growth of the single crystal.

[0030] Example 3: A method for preparing a GeTe single crystal comprises the following steps: S1. Raw material preparation: Weigh approximately 1g of bulk GeTe polycrystalline material prepared by the melting method as the reaction raw material and place it into a quartz tube with a carbon-coated inner wall. Evacuate the tube using a vacuum sealer. After the pressure in the tube drops to 6 Pa, purge the tube three times with argon gas. Then, vacuum seal the tube and set aside. The carbon coating step includes wetting the inner wall surface of the quartz tube with a small amount of alcohol, then heating the outer wall of the tube with a high-temperature (approximately 1600°C) inner flame from a gas-oxygen flame gun to carbonize the alcohol on the inner wall to form a carbon layer. S2 vapor deposition: This step is the same as in Example 2; S3. Ultrasonic cleaning: This step is the same as Example 2. The size of the obtained GeTe single crystal is 4-5 mm, and the number of single crystals obtained is relatively small, indicating that carbon coating on the inner wall of the quartz tube can reduce the probability of single crystal nucleation and is conducive to single crystal growth.

[0031] Example 4: A method for preparing a GeTe single crystal comprises the following steps: S1. Raw material preparation: This step is the same as in Example 3; S2. Vapor deposition: The quartz tube prepared in step S1 is placed horizontally in a holding furnace, and the quartz tube containing the raw materials is heated to 650°C at a rate of 200°C / h and kept at this temperature for 4 days to perform a vapor deposition reaction of GeTe, so that a GeTe single crystal is deposited and grown on the inner wall of the quartz tube; S3. Ultrasonic cleaning: This step is the same as Example 3. The size of the obtained GeTe single crystal is 5-6 mm, indicating that increasing the holding time can promote the growth of the single crystal.

[0032] Example 5: A Ge 0.9 Sb 0.1 The method for preparing a Te single crystal comprises the following steps: S1. Raw material preparation: Bulk Ge prepared by melting method 0.9 Sb 0.1 About 1 g of Te polycrystalline material was weighed as the reaction raw material and placed in a quartz tube with a carbon-coated inner wall. A vacuum tube sealer was used to evacuate the tube. After the pressure in the tube dropped to 6 Pa, the tube was purged with argon three times and then vacuum-sealed for later use. S2. Vapor deposition: This step is the same as in Example 3; S3. Ultrasonic cleaning: This step is the same as in Example 3. 0.9 Sb 0.1 Te single crystal. 0.9 Sb 0.1The size of Te single crystal is 4 to 5 mm.

[0033] Comparative Example 1: A method for preparing a GeTe single crystal comprises the following steps: S1. Raw material preparation: Weigh approximately 1 g of bulk GeTe polycrystalline material prepared by the melt method as the reaction raw material and place it into a clean quartz tube. Evacuate the tube using a vacuum sealer until the pressure inside the tube drops to 6 Pa. Purge the tube three times with argon gas, then vacuum seal and set aside. S2. Vapor deposition: This step is the same as in Example 4; S3. After removing the deposited product on the inner wall of the quartz tube in step S2, it was found that the grains were adhered and no independent GeTe single crystal could be obtained. The reason is that the deposition substrate was not carbon-coated, resulting in an uncontrolled number of single crystal nuclei, multiple single crystals nucleated and grew simultaneously, and contact and adhesion occurred under long-term heat preservation. Therefore, when producing GeTe single crystals of 4mm and above, in order to improve the quality of the single crystal, it is necessary to carbon-coat the inner wall of the quartz tube.

Claims

1. A GeTe single crystal, characterized in that: The chemical formula of the GeTe single crystal is Ge 1-x M x Te; wherein M includes at least one of Sb and Bi, 0≤x≤0.1; preferably, the size of the GeTe single crystal is 2 to 6 mm.

2. The GeTe single crystal according to claim 1, characterized in that 0＜x≤0.1。 3. A method for preparing a GeTe single crystal according to claim 1 or 2, characterized in that: include: (1) Selecting GeTe-based polycrystalline material as raw material, placing it in a clean quartz tube and vacuum sealing it; (2) placing the vacuum-sealed quartz tube horizontally into a holding furnace to perform a vapor deposition reaction of GeTe, so that a GeTe single crystal is deposited and grown on the inner wall of the quartz tube; (3) The deposited product on the inner wall of the quartz tube is taken out, and then cleaned and dried to obtain the GeTe single crystal.

4. The preparation method according to claim 3, characterized in that The GeTe-based polycrystalline material is in bulk or powder form.

5. The preparation method according to claim 3 or 4, characterized in that When the quartz tube is vacuum sealed, the gas pressure in the quartz tube is controlled to be less than 6 Pa, and argon gas is used for three times of gas purge.

6. The preparation method according to any one of claims 3 to 5, characterized in that First, a carbon plating treatment is performed on a portion of the inner wall of the quartz tube; the parameters of the carbon plating treatment include: first spraying a carbon source onto a portion of the inner wall of the quartz tube, and then performing a carbonization treatment; the carbon source is at least one of alcohol and acetone; and the temperature of the carbonization treatment is 1500-1600°C.

7. The preparation method according to any one of claims 3 to 6, characterized in that The parameters of the vapor deposition reaction include: the heating temperature of the quartz tube is 600-650° C.; the insulation time of the quartz tube is 2-4 days; and the heating rate of the quartz tube is 100-200° C. / h.

8. The preparation method according to any one of claims 3 to 7, characterized in that The cleaning method is ultrasonic cleaning; the number of ultrasonic cleaning is no less than 3 times, and each time lasts for 10 to 15 minutes.

9. Use of the GeTe single crystal according to claim 1 or 2 in the field of thermoelectric materials.

Images