A large-size SnSb2Te4 single crystal and its growth method

Abstract

The present invention belongs to the field of material preparation technology, specifically relating to a large-sized SnSb2Te4 single crystal and its growth method. The present invention provides an improved Bridgman method. This method first weighs appropriate Sn, Sb, and Te particles in an inert gas environment. A temperature ramp is then established. Specifically, the temperature is slowly raised to a first temperature at room temperature at a first rate and held at this temperature for 150 to 200 minutes. Subsequently, the temperature is slowly raised to a second temperature at a second rate. Subsequently, the temperature is lowered to a third temperature at a third rate and held at this temperature for 60 to 180 minutes. The crucible containing the materials is then lowered in a stepwise manner. This method can produce high-quality, large-sized SnSb2Te4 single crystals.

Description

Technical Field

[0001] The present 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 utilize the Seebeck and Peltier effects to directly convert heat into electricity, promising to alleviate the environmental and energy crises caused by the overexploitation and use of fossil fuels. Recently, layered IVV2Te4 compounds (where IV represents Ge, Sn, and Pb, and V represents Sb and Bi) have been recognized as promising thermoelectric materials due to their intrinsically low lattice thermal conductivity. Compared to GeSb2Te4-based materials, SnSb2Te4, with a similar crystal structure, has received relatively little attention in thermoelectric materials, despite its advantages such as heavier atomic mass and low cost. Furthermore, the limited research on SnSb2Te4-based thermoelectric materials that has been conducted has primarily focused on polycrystalline materials, while studies examining the thermoelectric properties of single crystal materials have yet to be reported. For example, the document "Study on Thermoelectric Transport Properties of Tin-Based Layered Compounds" (2021) discloses a method for preparing SnSb2Te4 samples. The method involves placing various metal materials in a sealed quartz tube, slowly heating the tube to 900°C (1173K) over 20 hours in a pit furnace, holding the temperature for 15 hours, and then cooling the sample to 400°C (673K). The ingot is then ground into powder and sintered into a fully dense sample using spark plasma. However, the SnSb2Te4 samples prepared by this method are all polycrystalline. Another example is the document "200°C Isothermal Section of the Sn-Sb-Te Ternary Alloy Phase Diagram" (2017), which discloses a method for preparing Sn-Sb-Te ternary alloy samples. The method involves placing various metal materials in a box-type resistance furnace for high-temperature melting and homogenization annealing. The sample annealing temperature is selected to be around 200°C below the liquidus. In this experiment, the sample was placed in a resistance furnace and held at 900°C for 180 minutes. The temperature was then lowered to 200°C at a rate of 3°C / min and held for 7 days. Finally, the alloy sample was quenched with water. However, the SnSb2Te4 samples prepared by this method were all polycrystalline, and large-scale single crystals of this compound have not yet been reported.

[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. During the crystal growth process, the furnace temperature of the equipment is controlled to be higher than the melting point of the compound, and then the crucible is slowly lowered from the high-temperature zone of the furnace to the low-temperature zone by the traction of the descending device to achieve slow crystallization of the melt, thereby growing large-sized single crystals. However, during the descent of the crucible, the vibration caused by external mechanical traction often brings adverse effects, such as an increase in 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-sized 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 solution based on an improved Bridgman method, as follows.

[0005] A method for preparing large-sized SnSb2Te4 single crystals, comprising a segmented temperature control program and a step-by-step lowering of a crucible, specifically comprising the following steps:

[0006] 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;

[0007] S02: placing the weighed raw materials into a quartz crucible, sealing the quartz crucible, and evacuating the quartz crucible to a vacuum;

[0008] S03: Hang the packaged quartz crucible in the middle of a vertical furnace, keep the quartz crucible stable, and set the temperature control program of the vertical furnace: at room temperature, slowly increase the temperature to the first temperature at a first rate, and keep it at this temperature for 150 to 200 minutes; then, slowly increase the temperature to the second temperature at a second rate; then, cool it to the third temperature at a third rate, and keep it at this temperature for 60 to 180 minutes;

[0009] Wherein, the first rate is greater than the second rate; the second rate is greater than the third rate;

[0010] Wherein, the first temperature is lower than the second temperature and the third temperature; the second temperature is higher than the third temperature;

[0011] The range of the first rate is 2-4°C / min; the range of the second rate is 1-2°C / min; the range of the third rate is 0.5-1°C / min;

[0012] The first temperature range is 500-700°C; the second temperature range is 900-1100°C; the third temperature range is 800-1000°C;

[0013] S04: Maintaining the third temperature, slowly lowering the packaged quartz crucible to the bottom of the vertical furnace, setting the descending mode to stepwise descent; the stepwise descent mode pauses for a period of time after descending a unit distance before descending again;

[0014] 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;

[0015] 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.

[0016] Furthermore, the rate of the step-by-step descent is set to 0.9-1.5 mm / h.

[0017] Furthermore, the unit distance of each step of the motor is set to include 2×10 -5 mm, 3×10 -5 mm, 4×10 -5 mm or 5×10 -5 mm.

[0018] Furthermore, the pause time for each descent of a unit distance is set to include 6s, 8s or 10s.

[0019] In some preferred embodiments, the pause time for each descent of a unit distance is set to 6 seconds or 8 seconds.

[0020] Furthermore, the total descending distance is set to 100-120 mm.

[0021] Furthermore, the inert gas environment includes argon, nitrogen or helium.

[0022] 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.

[0023] Furthermore, the purity of the Sn particles, Sb particles and Te particles is greater than 99%.

[0024] Furthermore, the vacuum degree range of the quartz crucible is 10 -5 ~10 -3 Pa.

[0025] In some preferred embodiments, the vacuum degree is 10 -5 Pa.

[0026] Large-sized SnSb2Te4 single crystals prepared by the above method.

[0027] Preferably, the size of the large-sized SnSb2Te4 single crystal is at the centimeter level.

[0028] Beneficial technical effects:

[0029] The present invention provides a method for preparing large-sized SnSb2Te4 single crystals based on an improved Bridgman method. The key points of this method include two main aspects: a segmented temperature control program and a step-by-step crucible descent method. Specifically, the segmented temperature control program (also known as a heating and soaking program) features three temperature control stages: heating, cooling, and cooling. The temperature adjustment rate in each stage of this three-stage program decreases sequentially. Overall, this segmented temperature control program first achieves complete melting of the raw materials by slowly increasing the temperature rapidly, then slowly, while avoiding thermal shock to the crucible caused by excessively rapid heating, which can lead to crystal defects. Furthermore, after slowly cooling to a specific temperature, the temperature is maintained above the melting point for a period of time to homogenize the melt and achieve thermodynamic equilibrium. Furthermore, in the step-by-step crucible descent method, the temperature at the solid-liquid interface is maintained stable by controlling the descent rate and dwell time, ensuring sufficient crystal growth while maintaining high process efficiency.

[0030] In summary, the method of the present invention not only has high process efficiency, but also reduces the impact of external mechanical traction vibration on crystal growth during the lowering of the crucible in the traditional Bridgman method, and ultimately achieves the growth of large-size SnSb2Te4 single crystals of good quality in a shorter process time. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the embodiments or the description of the prior art. In all drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the various elements or parts are 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 inventive work.

[0032] Figure 1 This is a schematic diagram of a vertical furnace in one embodiment of the present invention;

[0033] Figure 2This is a physical picture of a SnSb2Te4 single crystal ingot prepared in one embodiment of the present invention;

[0034] Figure 3 This is a photo of a cleaved SnSb2Te4 single crystal ingot prepared in one embodiment of the present invention;

[0035] Figure 4 This is the X-ray diffraction pattern of a SnSb2Te4 single crystal prepared in one embodiment of the present invention;

[0036] Figure 5 This is a scanning electron microscope image of a SnSb2Te4 single crystal prepared in one embodiment of the present invention (single crystal cleavage surface morphology);

[0037] Figure 6 This is a scanning electron microscope image of a SnSb2Te4 single crystal prepared in one embodiment of the present invention (morphology of the single crystal cross section perpendicular to the cleavage plane);

[0038] Figure 7 This is the energy dispersive X-ray spectroscopy (EDX) spectrum of the SnSb2Te4 single crystal prepared in one of the examples of the present invention. DETAILED DESCRIPTION

[0039] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only 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 efforts are within the scope of protection of the present invention.

[0040] As used herein, "and / or" includes any and all combinations of one or more of the associated listed items.

[0041] Herein, "plurality" means two or more than two, ie, it includes two, three, four, five, etc.

[0042] 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.

[0043] In this specification, certain embodiments may be disclosed in a format that is within a certain range. It should be understood that this description of "being within a certain range" is merely for convenience and brevity and should not be interpreted as a rigid limitation on the disclosed range. Therefore, the description of a range should be considered to have specifically disclosed all possible subranges and independent numerical values ​​within this range. For example, the description of a range of 1 to 6 should be considered to have specifically disclosed subranges 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.

[0044] Definition of noun:

[0045] The "step-by-step descent" described in the present invention means dividing the entire descent process into several 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 and ensure that the crystal can fully grow.

[0046] Example 1

[0047] This embodiment provides an overview of a method for preparing large-sized SnSb2Te4 single crystals using an improved Bridgman method.

[0048] S01: In an argon-filled operating environment, accurately weigh Sn particles (99.999%), Sb particles (99.999%), and Te particles (99.99%) according to a molar ratio of 1:2:4.

[0049] 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.

[0050] 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 The distance S between the thermocouple and the bottom of the furnace is approximately 120 mm. The quartz crucible is kept stable at this position, and the equipment's temperature control program is set to a staged temperature control program. This stage begins by slowly increasing the temperature to completely melt the raw material while avoiding thermal shock to the crucible caused by rapid temperature increases. Furthermore, the temperature is maintained above the melting point for a period of time to homogenize the melt, eliminate temperature gradients, and achieve thermodynamic equilibrium.

[0051] 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 cooled to the third temperature (T3) at the third rate (v3) and kept at this temperature for 60~180 minutes.

[0052] Among them, v1>v2>v3.

[0053] Among them, T1<T2; T1<T3. T2>T3.

[0054] The first rate (v1) is in the range of 2-4°C / min; the second rate (v2) is in the range of 1-2°C / min; and the third rate (v3) is in the range of 0.5-1°C / min.

[0055] 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.

[0056] S04: Maintaining the temperature at T3, slowly lower the packaged quartz crucible to the bottom of the furnace. Set the quartz crucible lowering mode to be step-by-step.

[0057] 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.

[0058] S05: until the quartz crucible drops to approximately the bottom of the furnace, the furnace is allowed to cool naturally to room temperature to obtain the large-sized SnSb2Te4 single crystal.

[0059] The large-sized SnSb2Te4 single crystal is of centimeter-level size.

[0060] Example 2

[0061] This embodiment provides another specific example of preparing large-sized SnSb2Te4 single crystals.

[0062] S01: In an argon-filled operating environment, accurately weigh Sn particles (99.999%), Sb particles (99.999%), and Te particles (99.99%) according to a molar ratio of 1:2:4. The total weight of the raw materials is 20 g.

[0063] 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 -5Pa.

[0064] S03: Suspend the encapsulated quartz crucible in the center of the vertical furnace, keeping it stable in this position. Then set the temperature control program for the equipment. At room temperature (30°C), slowly increase the temperature to 600°C (T1) at a rate of 2°C / min (v1) and hold at this temperature for 170 minutes. Subsequently, increase the temperature to 1000°C (T2) at a rate of 1°C / min (v2), then cool to 750°C (T3) at a rate of 0.5°C / min (V3), and hold at this temperature for 100 minutes.

[0065] 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.

[0066] 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 The motor pauses (delays) for 8 seconds each time it descends a unit distance; the total descending distance is 100~120mm.

[0067] S05: until the quartz crucible drops to approximately the bottom of the furnace, the furnace is allowed to cool naturally to room temperature to obtain the large-sized SnSb2Te4 single crystal.

[0068] The conical SnSb2Te4 single crystal ingot prepared in this example is shown in FIG. Figure 2 The conical single crystal ingot is about 40mm long and 13mm in diameter, with a smooth surface and metallic luster. After cleaving the single crystal ingot, it can be seen that the cleavage surface is flat and smooth, showing a mirror effect, such as Figure 3 shown.

[0069] The process of preparing large-sized SnSb2Te4 single crystals in this embodiment takes about 4 to 5 days.

[0070] Example 3

[0071] This embodiment provides a specific example of preparing large-sized SnSb2Te4 single crystals using another improved Bridgman method.

[0072] S01: In an argon-filled operating environment, accurately weigh Sn particles (99.999%), Sb particles (99.999%), and Te particles (99.99%) according to a molar ratio of 1:2:4. The total weight of the raw materials is 20 g.

[0073] 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.

[0074] S03: Suspend the encapsulated quartz crucible in the center of the vertical furnace, keeping it stable in this position. Then, set the temperature control program for the equipment. At room temperature (27°C), slowly increase the temperature to 650°C (T1) at a rate of 2°C / min (v1) and hold at this temperature for 180 minutes. Subsequently, increase the temperature to 1100°C (T2) at a rate of 1°C / min (v2), then cool to 900°C (T3) at a rate of 0.6°C / min (V3), and hold at this temperature for 120 minutes.

[0075] 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.

[0076] 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 -5 mm; the motor pauses (delays) for 8s every time it descends a unit distance; the total descending distance is 100~120mm.

[0077] S05: until the quartz crucible drops to approximately the bottom of the furnace, the furnace is allowed to cool naturally to room temperature to obtain the large-sized SnSb2Te4 single crystal.

[0078] The process of preparing large-sized SnSb2Te4 single crystals in this embodiment takes about 6 to 7 days.

[0079] Example 4

[0080] This embodiment provides a specific example of preparing large-sized SnSb2Te4 single crystals using another improved Bridgman method.

[0081] S01: In an argon-filled operating environment, accurately weigh Sn particles (99.999%), Sb particles (99.999%), and Te particles (99.99%) according to a molar ratio of 1:2:4. The total weight of the raw materials is 20 g.

[0082] 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.

[0083] S03: Suspend the encapsulated quartz crucible in the center of the vertical furnace, keeping it stable in this position. Then, set the temperature control program for the equipment. At room temperature (28°C), slowly increase the temperature to 700°C (T1) at a rate of 3°C / min (v1) and hold at this temperature for 200 minutes. Subsequently, increase the temperature to 1000°C (T2) at a rate of 2°C / min (v2), then cool to 850°C (T3) at a rate of 0.5°C / min (V3), and hold at this temperature for 150 minutes.

[0084] 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.

[0085] 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.

[0086] S05: until the quartz crucible drops to approximately the bottom of the furnace, the furnace is allowed to cool naturally to room temperature to obtain the large-sized SnSb2Te4 single crystal.

[0087] The process of preparing large-sized SnSb2Te4 single crystals in this embodiment takes about 4 to 5 days.

[0088] Example 5

[0089] 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 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 images intuitively reflect 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.

[0090] Example 6

[0091] The step-by-step lowering method of the quartz crucible provided by the present invention is further verified.

[0092] Table 1

[0093]

[0094] It should be noted that, in this document, the terms "comprises," "includes," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, article, or apparatus comprising a series of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or apparatus comprising the element.

[0095] 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 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 protected by the present invention.

Claims

1. A method for preparing large-sized 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: placing 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 a vertical furnace, keep the quartz crucible stable, and set the temperature control program of the vertical furnace: at room temperature, slowly increase the temperature to the first temperature at a first rate, and keep it at this temperature for 150 to 200 minutes; then, slowly increase the temperature to the second temperature at a second rate; then, cool it to the third temperature at a 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 range of the first rate is 2-4°C / min; the range of the second rate is 1-2°C / min; the range of the third rate is 0.5-1°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 bottom of the vertical furnace, setting the descending mode to stepwise descent; the stepwise descent mode pauses for a period of time after descending a unit distance before descending again; The step-by-step descending speed is set to 0.5-2.5 mm / h, and 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, wherein The rate of the step-by-step descent is set to 0.9-1.5 mm / h.

3. The method according to claim 1, wherein 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, wherein The pause time for each unit of distance dropped is set to 6s, 8s or 10s.

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

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

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

8. The method according to claim 1, wherein 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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