Large-size SnSb2Te4 single crystal and growth method thereof

Abstract

The invention belongs to the technical field of material preparation, and particularly relates to a large-size SnSb2Te4 single crystal and a growth method thereof. The invention provides an improved Bridgman method, which comprises the following steps of: firstly, weighing proper Sn particles, Sb particles and Te particles in an inert gas environment, then setting a heating program, specifically, slowly heating to a first temperature at a first speed at a room temperature, and keeping the temperature for 150-200 minutes at the temperature; then, slowly raising the temperature to a second temperature at a second speed; then, the temperature is reduced to a third temperature at a third speed, and heat preservation is conducted for 60-180 min at the temperature; the crucible loaded with the material is then lowered step by step. According to the method disclosed by the invention, the SnSb2Te4 single crystal with high quality and large size can be prepared.

Description

Technical Field

[0001] The invention belongs to the technical field of material preparation, and in particular relates to a large-size SnSb2Te4 single crystal and a growth method thereof. Background Art

[0002] Thermoelectric materials use the Seebeck effect and the Peltier effect to achieve direct conversion of heat and electricity, and are expected to alleviate the environmental and energy crisis caused by the overexploitation and use of fossil fuels. Recently, layered IVV2Te4 compounds (IV represents Ge, Sn and Pb, and V represents Sb and Bi) are considered to be promising thermoelectric materials because of their intrinsic low lattice thermal conductivity. Compared with GeSb2Te4-based materials, SnSb2Te4 with a similar crystal structure has little attention in thermoelectric materials even though it has advantages such as heavier atomic mass and low cost. On the other hand, the few existing studies on SnSb2Te4-based thermoelectric materials mainly focus on polycrystalline materials, and no relevant research on the thermoelectric properties of its single crystal materials has been reported. For example, the document "Study on Thermoelectric Transport Properties of Tin-Based Laminated Compounds" (2021) discloses a method for preparing SnSb2Te4 samples, which places each metal material in a quartz tube, seals the quartz tube, and then places it in a pit furnace and slowly heats it to 900°C (1173K) in 20 hours, keeps it warm for 15 hours, and then cools it to 400°C (673K). The ingot is further ground into powder and sintered into a completely dense sample by spark plasma. However, the SnSb2Te4 samples prepared by this document method are all polycrystalline. For another example, the document "200°C Isothermal Section of Sn-Sb-Te Ternary Alloy Phase Diagram" (2017) discloses a method for preparing Sn-Sb-Te ternary alloy samples, which places each metal material in a box-type resistance furnace for high-temperature melting and homogenization annealing. The sample annealing temperature is selected to be about 200°C below the liquidus. The experiment placed the sample in a resistance furnace and kept it at 900℃ for 180min, then cooled it to 200℃ at a rate of 3℃ / min and kept it at that temperature for 7 days, and finally quenched the alloy sample with water as the quenching medium. However, the SnSb2Te4 samples prepared by this method are all polycrystalline, and there is no report on large-sized single crystals of this compound.

[0003] 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 large-sized single crystals. However, during the descent of the crucible, 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. However, the Bridgman method is more efficient in preparing single crystals and has a high degree of automation. Based on this, it is necessary to propose new improvement and optimization strategies for the traditional crucible descent method. Summary of the invention

[0004] The object of the present invention is to provide a large-size SnSb2Te4 single crystal and a preparation method thereof, so as to partially solve or alleviate the above-mentioned deficiencies in the prior art. Specifically, the present invention aims to provide a preparation scheme based on an improved Bridgman method, as follows.

[0005] A method for preparing a large-size SnSb2Te4 single crystal, the method comprising a segmented temperature control program and a step-by-step descent of a crucible, specifically comprising the following steps: S01: weighing Sn particles, Sb particles and Te particles in an inert gas environment, wherein the molar ratio of the Sn particles, Sb particles and Te particles is 1:2:4; S02: putting the weighed raw materials into a quartz crucible, sealing the quartz crucible, and evacuating the quartz crucible to a vacuum; S03: Hang the packaged quartz crucible in the middle of the vertical furnace, keep the quartz crucible stable, and set the temperature control program of the vertical furnace: slowly increase the temperature to the first temperature at the first rate at room temperature, and keep it at this temperature for 150 to 200 minutes; then, slowly increase the temperature to the second temperature at the second rate; then, cool down to the third temperature at the third rate, and keep it at this temperature for 60 to 180 minutes; Wherein, the first rate is greater than the second rate; the second rate is greater than the third rate; Wherein, the first temperature is lower than the second temperature and the third temperature; the second temperature is higher than the third temperature; The first rate ranges from 2 to 4°C / min; the second rate ranges from 1 to 2°C / min; the third rate ranges from 0.5 to 1°C / min; The first temperature range is 500-700°C; the second temperature range is 900-1100°C; the third temperature range is 800-1000°C; S04: maintaining the third temperature, slowly lowering the packaged quartz crucible to the bottom of the furnace chamber of the vertical furnace, and setting the descending mode to step-by-step descent; the step-by-step descent mode is to pause for a period of time after descending a unit distance before descending; The step-by-step descending rate is set to 0.5~2.5mm / h; the unit distance of the motor descending per step is set to 2~5×10 -5 mm; the pause time for each unit of descending distance is 6~10s; the total descending distance of the (crucible) is 100~150mm; S05: When the quartz crucible descends to the bottom of the vertical furnace, it is naturally cooled to room temperature (inside the vertical furnace) to obtain the large-sized SnSb2Te4 single crystal.

[0006] Furthermore, the step-by-step descent rate is set to 0.9-1.5 mm / h.

[0007] Further, the unit distance of the motor falling in each step is set to include 2×10 -5 mm, 3×10 -5 mm, 4×10 -5 mm or 5×10 -5 mm.

[0008] Furthermore, the pause time for each unit distance dropped is set to 6s, 8s or 10s.

[0009] In some preferred embodiments, the pause time for each descent of a unit distance is set to 6s or 8s.

[0010] Furthermore, the total descending distance is set to 100-120 mm.

[0011] Furthermore, the inert gas environment includes argon, nitrogen or helium.

[0012] Furthermore, the total weighing amount of the Sn particles, Sb particles and Te particles is 10-50 g, which can be reasonably adjusted according to the size of the crucible of the equipment.

[0013] Furthermore, the purity of the Sn particles, Sb particles and Te particles is greater than 99%.

[0014] Furthermore, the vacuum degree in the quartz crucible ranges from 10 -5 ~10 -3 Pa.

[0015] In some preferred embodiments, the vacuum degree is 10 -5 Pa.

[0016] The large-sized SnSb2Te4 single crystal prepared by the above method.

[0017] Preferably, the size of the large-sized SnSb2Te4 single crystal is at the centimeter level.

[0018] Beneficial technical effects: The present invention provides a method for preparing large-size SnSb2Te4 single crystals based on an improved Bridgman method. The key points of the method of the present invention mainly include two aspects: setting a segmented temperature control program and a step-by-step descent method of the crucible. Specifically, the segmented temperature control program (also known as a heating and soaking program) sets three sections of temperature control, namely heating, heating and cooling. In the three-section temperature control program, the rate of adjusting the temperature in each section is sequentially reduced. Overall, the segmented temperature control program first melts the raw material completely by slowly heating up first fast and then slowly, while avoiding the thermal shock to the crucible caused by too fast heating, and then causing crystal defects. Further, after slowly cooling to a specific temperature, the material is kept warm for a period of time above the melting point to homogenize the melt and reach thermodynamic equilibrium. Further, in the step-by-step descent method of the crucible, the temperature of the solid-liquid interface is kept stable by controlling the descent rate and the dwell time, ensuring that the crystal can grow fully, while ensuring a high process efficiency.

[0019] In summary, the method of the present invention not only has high process efficiency, but also reduces the influence of external mechanical traction vibration on crystal growth during the lowering of the crucible in the traditional Bridgman method, and finally realizes the growth of large-size SnSb2Te4 single crystals with good quality in a shorter process time. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] 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.

[0021] Figure 1 It is a schematic diagram of a vertical furnace in one embodiment of the present invention; Figure 2 This is a physical picture of a SnSb2Te4 single crystal ingot prepared in one of the embodiments of the present invention; Figure 3 This is a physical picture of a cleaved SnSb2Te4 single crystal ingot prepared in one of the embodiments of the present invention; Figure 4This is an X-ray diffraction pattern of a SnSb2Te4 single crystal prepared in one embodiment of the present invention; Figure 5 This is a scanning electron microscope image of a SnSb2Te4 single crystal prepared in one of the embodiments of the present invention (morphology of the single crystal cleavage surface); Figure 6 This is a scanning electron microscope image of a SnSb2Te4 single crystal prepared in one of the embodiments of the present invention (morphology of the single crystal cross section perpendicular to the cleavage plane); Figure 7 This is an energy dispersive X-ray spectroscopy (EDX) spectrum of a SnSb2Te4 single crystal prepared in one of the embodiments of the present invention. DETAILED DESCRIPTION

[0022] 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 creative work are within the scope of protection of the present invention.

[0023] Herein "and / or" includes any and all combinations of one or more of the associated listed items.

[0024] Herein, "plurality" means two or more than two, ie, it includes two, three, four, five, etc.

[0025] 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, even more typically + / - 0.5% of the stated value.

[0026] In this specification, some embodiments may be disclosed in a format of being in a certain range. It should be understood that this description of "being in 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 description of the range 1 to 6 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, such as 1, 2, 3, 4, 5 and 6. Regardless of the breadth of the range, the above rules apply.

[0027] Definition of noun: The "step-by-step descent" described in the present invention refers to dividing the entire descent process into a number of small steps, with each step having a fixed descent distance (x); after completing each preset step, the system will pause for a period of time (called a delay) to keep the temperature of the solid-liquid interface stable, thereby ensuring that the crystal can grow fully.

[0028] Example 1 This embodiment provides an overview of a method for preparing large-sized SnSb2Te4 single crystals using an improved Bridgman method.

[0029] S01: In an argon-filled operating environment, Sn particles (99.999%), Sb particles (99.999%), and Te particles (99.99%) were accurately weighed in a molar ratio of 1:2:4.

[0030] S02: Put the weighed raw materials into a quartz crucible with a conical bottom, and seal the quartz crucible. Pump the pressure in the quartz tube to 10 -5 ~10 -3 Pa.

[0031] S03: Segmented temperature control program: Hang the packaged quartz crucible in the middle of the vertical furnace (the location where the thermocouple is set in the equipment is the middle, see the schematic diagram Figure 1 , where the distance S from the thermocouple to the bottom of the furnace is about 120mm), the quartz crucible is kept stable at this position, and then the temperature control program of the equipment is set to a segmented temperature control program. In this stage, the raw materials are first melted completely by slowly heating up, while avoiding thermal shock to the crucible caused by too fast heating up. Furthermore, the material is kept warm for a period of time above the melting point to homogenize the melt, eliminate the temperature gradient and reach thermodynamic equilibrium.

[0032] Specifically, at room temperature, the temperature is slowly increased to the first temperature (T1) at the first rate (v1), and kept at this temperature for 150-200 minutes; then, the temperature is slowly increased to the second temperature (T2) at the second rate (v2); then, the temperature is reduced to the third temperature (T3) at the third rate (v3) and kept at this temperature for 60-180 minutes.

[0033] Among them, v1>v2>v3.

[0034] Among them, T1<T2; T1<T3. T2>T3.

[0035] Among them, the range of the first rate (v1) is 2~4℃ / min; the range of the second rate (v2) is 1~2℃ / min; the range of the third rate (v3) is 0.5~1℃ / min.

[0036] Wherein, the first temperature (T1) ranges from 500 to 700°C; the second temperature (T2) ranges from 900 to 1100°C; and the third temperature (T3) ranges from 800 to 1000°C.

[0037] S04: Maintaining the temperature of T3, slowly lower the packaged quartz crucible to the bottom of the furnace, and setting the quartz crucible lowering mode, which is step-by-step lowering.

[0038] The descending speed is set to N, which is 0.5~2.5mm / h; the unit distance of the motor descending per step is set to x, which is 2~5×10 -5 mm; the motor pauses every time it descends a unit distance, and the pause time (delay) t is 6~10s.

[0039] S05: until the quartz crucible drops to approximately the bottom end of the furnace, the furnace is allowed to cool naturally to room temperature to obtain the large-sized SnSb2Te4 single crystal.

[0040] The large-sized SnSb2Te4 single crystal is of centimeter-level size.

[0041] Example 2 This embodiment provides another specific example of preparing large-sized SnSb2Te4 single crystals.

[0042] S01: In an argon-filled operating environment, Sn particles (99.999%), Sb particles (99.999%), and Te particles (99.99%) were accurately weighed according to a molar ratio of 1:2:4, and the total weight of the raw materials was 20 g.

[0043] S02: Put the weighed raw materials into a quartz crucible with a conical bottom, and seal the quartz crucible. Pump the pressure in the quartz tube to 10 -5 Pa.

[0044] S03: Hang the packaged quartz crucible in the middle of the vertical furnace, keep the quartz crucible stable in this position, and then set the temperature control program of the equipment. At room temperature (30°C), slowly increase the temperature to 600°C (T1) at a rate of 2°C / min (v1), and keep it at this temperature for 170 minutes. Subsequently, increase the temperature to 1000°C (T2) at a rate of 1°C / min (v2), and then cool it to 750°C (T3) at a rate of 0.5°C / min (V3), and keep it at this temperature for 100 minutes.

[0045] S04: Maintaining the temperature at 750°C, slowly lower the packaged quartz crucible to the bottom of the furnace. Set the quartz crucible lowering mode to step-by-step lowering.

[0046] The descending speed N is set to 1.35 mm / h; the unit distance x of the motor descending per step is set to 3×10 -5 mm; the motor pauses (delays) for 8s every time it descends a unit distance; the total descending distance is 100~120mm.

[0047] S05: until the quartz crucible drops to approximately the bottom end of the furnace, the furnace is allowed to cool naturally to room temperature to obtain the large-sized SnSb2Te4 single crystal.

[0048] The conical SnSb2Te4 single crystal ingot prepared in this example is shown in FIG. Figure 2 The conical single crystal ingot is about 40 mm long and 13 mm in diameter. Its surface is relatively smooth and has a metallic luster. After cleaving the single crystal ingot, it can be seen that its cleavage surface is flat and smooth, showing a mirror effect, such as Figure 3 shown.

[0049] The process of preparing large-sized SnSb2Te4 single crystals in this embodiment takes about 4 to 5 days.

[0050] Example 3 This embodiment provides another specific example of preparing large-sized SnSb2Te4 single crystals by using the improved Bridgman method.

[0051] S01: In an argon-filled operating environment, Sn particles (99.999%), Sb particles (99.999%), and Te particles (99.99%) were accurately weighed according to a molar ratio of 1:2:4, and the total weight of the raw materials was 20 g.

[0052] S02: Put the weighed raw materials into a quartz crucible with a conical bottom, and seal the quartz crucible. Pump the pressure in the quartz tube to 10 -5 Pa.

[0053] S03: Hang the packaged quartz crucible in the middle of the vertical furnace, keep the quartz crucible stable in this position, and then set the temperature control program of the equipment. At room temperature (27°C), slowly increase the temperature to 650°C (T1) at a rate of 2°C / min (v1), and keep it at this temperature for 180 minutes. Subsequently, increase the temperature to 1100°C (T2) at a rate of 1°C / min (v2), and then cool it to 900°C (T3) at a rate of 0.6°C / min (V3), and keep it at this temperature for 120 minutes.

[0054] S04: Maintaining the temperature at 900°C, slowly lower the packaged quartz crucible to the bottom of the furnace. Set the quartz crucible lowering mode to step-by-step lowering.

[0055] The descending speed N is set to 0.9 mm / h; the unit distance x of the motor descending per step is set to 2×10 -5mm; the motor pauses (delays) for 8s every time it descends a unit distance; the total descending distance is 100~120mm.

[0056] S05: until the quartz crucible drops to approximately the bottom end of the furnace, the furnace is allowed to cool naturally to room temperature to obtain the large-sized SnSb2Te4 single crystal.

[0057] The process of preparing large-sized SnSb2Te4 single crystals in this embodiment takes about 6 to 7 days.

[0058] Example 4 This embodiment provides another specific example of preparing large-sized SnSb2Te4 single crystals by using the improved Bridgman method.

[0059] S01: In an argon-filled operating environment, Sn particles (99.999%), Sb particles (99.999%), and Te particles (99.99%) were accurately weighed according to a molar ratio of 1:2:4, and the total weight of the raw materials was 20 g.

[0060] S02: Put the weighed raw materials into a quartz crucible with a conical bottom, and seal the quartz crucible. Pump the pressure in the quartz tube to 10 -4 Pa.

[0061] S03: Hang the packaged quartz crucible in the middle of the vertical furnace, keep the quartz crucible stable in this position, and then set the temperature control program of the equipment. At room temperature (28°C), slowly increase the temperature to 700°C (T1) at a rate of 3°C / min (v1), and keep it at this temperature for 200 minutes. Subsequently, increase the temperature to 1000°C (T2) at a rate of 2°C / min (v2), and then cool it to 850°C (T3) at a rate of 0.5°C / min (V3), and keep it at this temperature for 150 minutes.

[0062] S04: Maintaining the temperature at 850°C, slowly lower the packaged quartz crucible to the bottom of the furnace. Set the quartz crucible lowering mode to step-by-step lowering.

[0063] The descending speed N is set to 1.44 mm / h; the unit distance x of the motor descending per step is set to 4×10 -5 mm; the motor pauses (delays) for 10s every time it descends a unit distance; the total descending distance is 100~120mm.

[0064] S05: until the quartz crucible drops to approximately the bottom end of the furnace, the furnace is allowed to cool naturally to room temperature to obtain the large-sized SnSb2Te4 single crystal.

[0065] The process of preparing large-sized SnSb2Te4 single crystals in this embodiment takes about 4 to 5 days.

[0066] Example 5 The phase, micromorphology, and element distribution of the large-sized SnSb2Te4 single crystal prepared in Example 2 were characterized. The X-ray diffraction pattern of the SnSb2Te4 single crystal sample obtained in Example 2 was collected by an X-ray diffractometer (see Figure 4 The cleavage surface morphology and cross-section morphology perpendicular to the cleavage surface of the SnSb2Te4 single crystal sample obtained in Example 2 were characterized by scanning electron microscopy (SEM-FIB, Thermoscientific Helios 5 CX). The SEM image intuitively reflects the layered stacking characteristics of the single crystal sample (see Figure 5 and Figure 6 ). Figure 7 Energy dispersive X-ray spectroscopy (EDX) characterization of the SnSb2Te4 single crystal sample obtained in Example 2 shows the uniform distribution of elements in the sample.

[0067] Example 6 The step-by-step lowering method of the quartz crucible provided by the present invention is further verified.

[0068] Table 1 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.

[0069] 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 methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the enlightenment of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which all fall within the protection of the present invention.

Claims

1. A method for preparing large-size SnSb2Te4 single crystals, characterized in that: The method comprises the following steps: S01: weighing Sn particles, Sb particles and Te particles in an inert gas environment, wherein the molar ratio of the Sn particles, Sb particles and Te particles is 1:2:4; S02: putting the weighed raw materials into a quartz crucible, sealing the quartz crucible, and evacuating the quartz crucible to a vacuum; S03: Hang the packaged quartz crucible in the middle of the vertical furnace, keep the quartz crucible stable, and set the temperature control program of the vertical furnace: slowly increase the temperature to the first temperature at the first rate at room temperature, and keep it at this temperature for 150 to 200 minutes; then, slowly increase the temperature to the second temperature at the second rate; then, cool down to the third temperature at the third rate, and keep it at this temperature for 60 to 180 minutes; Wherein, the first rate is greater than the second rate; the second rate is greater than the third rate; Wherein, the first temperature is lower than the second temperature and the third temperature; the second temperature is higher than the third temperature; The first rate ranges from 2 to 4°C / min; the second rate ranges from 1 to 2°C / min; the third rate ranges from 0.5 to 1°C / min; The first temperature range is 500-700°C; the second temperature range is 900-1100°C; the third temperature range is 800-1000°C; S04: maintaining the third temperature, slowly lowering the quartz crucible to the lowest end of the furnace of the vertical furnace, and setting the descending mode to step-by-step descending; the step-by-step descending mode is to pause for a period of time after descending a unit distance before descending; The step-by-step descending rate is set to 0.5-2.5 mm / h; the unit distance of each step of the motor is set to 2-5×10 -5 mm; the pause time for each unit of descending distance is 6~10s; the total descending distance is 100~150mm; S05: When the quartz crucible descends to the bottom of the vertical furnace, it is naturally cooled to room temperature to obtain the large-sized SnSb2Te4 single crystal.

2. The method according to claim 1, characterized in that The step-by-step descent rate is set to 0.9-1.5 mm / h.

3. The method according to claim 1, characterized in that Set the unit distance of the motor to 2×10 - 5 mm, 3×10 -5 mm, 4×10 -5 mm or 5×10 -5 mm.

4. The method according to claim 1, characterized in that The pause time for each unit distance dropped is set to 6s, 8s or 10s.

5. The method according to claim 1, characterized in that The descending distance is set to 100-120 mm.

6. The method according to claim 1, characterized in that The inert gas environment includes argon, nitrogen or helium.

7. The method according to claim 1, characterized in that The total weighing amount of the Sn particles, Sb particles and Te particles is 10-50 g.

8. The method according to claim 1, characterized in that The purity of the Sn particles, Sb particles and Te particles is greater than 99%.

9. The method according to claim 1, wherein: The vacuum range of the quartz crucible is 10 -5 ~10 -3 Pa.

10. A large-sized SnSb2Te4 single crystal prepared by the method according to any one of claims 1 to 9.

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