Method for synthesizing Se crystal at high temperature and high pressure

Abstract

The invention discloses a method for synthesizing Se crystals at high temperature and high pressure. Relates to the technical field of Se crystal synthesis. The method comprises the following steps that Se powder serves as a starting raw material and is placed in a sealed environment, the pressure is increased to 4.8-5.2 GPa in a gradient mode, then the temperature is increased to 650-700 DEG C in a gradient mode, heat preservation and pressure maintaining reaction is conducted for 25-35 min, quenching is conducted, cooling and pressure relief are conducted to the room temperature and the normal pressure, and the Se crystal is obtained. The high-quality and large-size Se crystal is synthesized, a problem in the technical field of material synthesis and preparation at present is solved, and a guarantee is provided for experimental research of Se crystals. By adopting the growth mode provided by the invention, the negative influence of the volatility of Se on the crystal growth can be effectively reduced, and no new impurity is introduced; under the growth condition adopted by the invention, the crystal structure of the grown Se is not distorted, and the problem that the growth of the high-quality Se crystal is partially insufficient at high temperature and high pressure can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of Se crystal synthesis, and in particular to a method for synthesizing Se crystals at high temperature and high pressure. Background Art

[0002] Se crystal, also known as selenium crystal, is a crystalline material composed of selenium. The synthesis methods of Se crystals mainly include chemical vapor deposition, hydrothermal method, physical vapor deposition, solution synthesis method and van der Waals epitaxy. Among them, the solid-phase synthesis method forms Se crystals by reacting Se powder under high temperature and high pressure conditions. This method is suitable for the preparation of large-sized Se crystals, but the Se in this synthesis method is volatile, which makes it difficult to maintain a constant Se concentration during the single crystal growth process. Fluctuations in concentration will lead to unstable crystal quality and difficult to accurately control the growth rate, which in turn affects the consistency and performance of the final product.

[0003] Due to the hexagonal lattice structure of Se crystals, surface cracks are prone to form during crystal growth, especially when growing larger single crystals. This severely limits the production of large, high-quality Se single crystals. The preparation of high-purity Se is complex and difficult. Failure to strictly control impurity levels during single crystal growth can negatively impact the electronic properties and structural quality of the resulting single crystal, reducing the product's application value. Furthermore, growing Se single crystals under high-temperature, high-pressure conditions presents further challenges: Se evaporates at relatively low temperatures, but its volatility is even more pronounced under high-temperature, high-pressure environments, particularly at temperatures above 600°C. This makes maintaining a stable Se concentration in high-temperature environments extremely challenging, significantly impacting crystal growth and quality. Se can undergo phase transitions under high-temperature, high-pressure conditions, and its solubility varies significantly with temperature and pressure. This complicates solubility control during crystal growth, increasing the difficulty and uncertainty of the growth process. Se crystals can accumulate significant stress during growth under high-temperature, high-pressure conditions, which can lead to the formation of cracks and other defects. Therefore, stress management during growth is crucial. Under high pressure conditions, the crystal structure of Se may change. Pressure changes can affect the arrangement of Se molecules and may produce new phases or undesirable defect structures. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for synthesizing Se crystals at high temperature and high pressure to solve the problem of unstable quality of Se crystals.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for synthesizing Se crystals at high temperature and high pressure, comprising the following steps:

[0007] Se powder is used as the starting material and placed in a sealed environment. The pressure is first gradually increased to 4.8-5.2GPa, and then the temperature is gradually increased to 650-700℃. The reaction is maintained at this temperature and pressure for 25-35 minutes, and then quenched. The temperature is then reduced and the pressure is released to room temperature (25-30℃) and normal pressure to obtain Se crystals.

[0008] As a further solution of the present invention, the gradient pressure increase includes: increasing the pressure to 0.5-0.6 GPa within 30-40 minutes, and then increasing the pressure to 4.8-5.2 GPa within 110-120 minutes, and the total gradient pressure increase time is 140-160 minutes.

[0009] Furthermore, the gradient pressure increase includes: increasing the pressure to 0.5 GPa within 30 minutes, and then increasing the pressure to 5 GPa within 120 minutes, and the total gradient pressure increase time is 150 minutes.

[0010] As a further solution of the present invention, the gradient heating includes: heating to 150-180°C within 8-12 minutes, then heating to 500-600°C within 8-12 minutes, and finally heating to 650-700°C within 8-12 minutes. The total gradient heating time is 24-36 minutes.

[0011] Furthermore, the gradient heating includes: heating to 170°C within 10 minutes, heating to 580°C within 10 minutes, and finally heating to 650°C within 10 minutes. The total time of the gradient heating is 30 minutes.

[0012] As a further solution of the present invention, the pressure relief time is 150-200 minutes, and the pressure relief rate is controlled to slowly release the pressure to normal pressure.

[0013] As a further solution of the present invention, the Se powder is pressed into a cylindrical shape of 3.2 mm in height and 3.5 mm in diameter before the reaction as a sample, and placed in a BN (boron nitride) tube with BN as the pressure transmission medium.

[0014] As a further embodiment of the present invention, the sealed environment comprises an octahedral high-pressure device capable of providing high-temperature and high-pressure reaction conditions. The device comprises a high-pressure synthesis assembly block, into which a BN tube filled with Se powder is assembled. The sealed environment is intended to prevent Se volatilization from affecting product performance. The high-temperature and high-pressure reaction device can be selected based on actual conditions to achieve or satisfy the crystal growth conditions.

[0015] Furthermore, the assembly method of the BN tube filled with Se powder in the high-pressure synthesis assembly block includes: sealing the upper and lower openings of the BN tube filled with Se powder with BN discs, then covering the outer layer of the BN tube with a layer of graphite tube as a heating layer, sealing the upper and lower openings with a graphite gasket with a hole, inserting a molybdenum column into the hole as a conductive layer, and sealing the outside of the graphite layer with a layer of zirconia tube as an insulation layer.

[0016] As a further solution of the present invention, the size of the Se crystal is ≥500 μm, the crystal is off-white, the surface coating is brown, and the synthesized Se crystal is a hexagonal crystal system.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The present invention synthesizes high-quality, large-sized Se crystals through a high-temperature and high-pressure method, which solves a difficult problem in the current field of material synthesis and preparation technology and provides a guarantee for experimental research on Se crystals.

[0019] 2. The growth method provided by the present invention can effectively reduce the negative impact of Se volatility on crystal growth without introducing new impurities; under the growth conditions adopted by the present invention, the crystal structure of the grown Se is not distorted, which can effectively solve the problem of insufficient growth of high-quality Se crystals under high temperature and high pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a scanning electron microscope image of the product prepared in Example 1;

[0021] Figure 2 This is a Raman image of the product prepared in Example 1;

[0022] Figure 3 The product prepared in Example 1 was at 236 cm- 1 Polarized Raman characteristic image under vertical light incidence conditions;

[0023] Figure 4 The product prepared in Example 1 was at 236 cm- 1 Polarized Raman characteristic image under parallel light incident conditions at ;

[0024] Figure 5 This is the Raman image of the product prepared in Comparative Example 2. DETAILED DESCRIPTION

[0025] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0026] The terms used in the examples of this application are for the purpose of describing specific implementation rules only and are not intended to limit this application. The singular forms "a", "an", "the" and "the" used in the implementation rules of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0027] It should be understood that in the various embodiments of the present application, the size of the serial number of each process does not mean the order of execution. Some or all steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0028] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass described in the examples of this application may be a mass unit known in the chemical industry, such as μg, mg, g, kg, etc.

[0029] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0030] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0031] The preparation of high-purity Se crystals is complex and difficult. Failure to strictly control impurity levels during single crystal growth can negatively impact the electronic properties and structural quality of the resulting single crystal, reducing the product's application value. Se crystals, grown in high-temperature, high-pressure environments, are prone to significant stress accumulation during growth. These stresses can lead to cracks or other defects, resulting in structural distortion of the Se crystal.

[0032] To this end, the present application provides a method for synthesizing Se crystals at high temperature and high pressure, specifically comprising the following steps:

[0033] Se powder is used as the starting material and placed in a sealed environment. The pressure is first gradually increased to 4.8-5.2 GPa, and then the temperature is gradually increased to 650-700°C. The reaction is maintained at this temperature and pressure for 25-35 minutes, and then quenched, cooled and decompressed to room temperature and normal pressure to obtain Se crystals.

[0034] In a specific implementation case, the gradient pressurization process is specifically as follows: the pressure is increased to 0.5-0.6 GPa within 30-40 minutes, and then increased to 4.8-5.2 GPa within 110-120 minutes, and the total gradient pressurization time is 140-160 minutes;

[0035] Preferably, the gradient pressure increasing process is as follows: increasing the pressure to 0.5 GPa within 30 minutes, and then increasing the pressure to 5 GPa within 120 minutes, and the total gradient pressure increasing time is 150 minutes.

[0036] In a specific embodiment, the gradient temperature increase includes: increasing the temperature to 150-180°C within 8-12 minutes, then increasing the temperature to 500-600°C within 8-12 minutes, and finally increasing the temperature to 650-700°C within 8-12 minutes. The total gradient temperature increase time is 24-36 minutes.

[0037] Preferably, the heating rate is: gradient heating includes: heating to 170°C within 10 minutes, then heating to 580°C within 10 minutes, and finally heating to 650°C within 10 minutes. The total time of gradient heating is 30 minutes.

[0038] In a specific implementation case, the pressure relief time is 150-200 minutes. Too fast pressure relief will damage the tungsten carbide anvil used in the experiment.

[0039] In a specific implementation case, Se powder was first pressed into a cylindrical shape with a height of 3.2 mm and a diameter of 3.5 mm as a sample before the reaction, and placed in a BN tube.

[0040] In one specific embodiment, the sealed environment comprises an octahedral high-pressure device capable of providing high-temperature and high-pressure reaction conditions. The device contains a high-pressure synthesis assembly block, into which a BN tube filled with Se powder is assembled. The sealed environment prevents Se volatilization from affecting product performance. Depending on the actual situation, the high-temperature and high-pressure reaction device can be selected to achieve or satisfy the crystal growth conditions.

[0041] In a specific implementation case, the assembly method of the BN tube filled with Se powder in the high-pressure synthesis assembly block includes: sealing the upper and lower openings of the BN tube filled with Se powder with BN discs, then putting a layer of graphite tube on the outer layer of the BN tube as a heating layer, sealing the upper and lower openings with graphite gaskets with holes, inserting molybdenum columns into the holes as a conductive layer, and sealing the outside of the graphite layer with a layer of zirconia tube as an insulation layer.

[0042] The following is further described with reference to specific embodiments.

[0043] Example 1

[0044] This embodiment provides a method for synthesizing Se crystals at high temperature and high pressure, comprising the following steps:

[0045] S1: Assemble the sealed environment:

[0046] Analytically pure Se powder is used as a starting material; a tablet press is used to press the Se powder into a cylinder with a height of 3.2 mm and a diameter of 3.5 mm, which is then placed in a BN tube with BN as a pressure transmission medium; the upper and lower openings of the BN tube filled with the Se powder sample are sealed with BN discs, and a graphite tube is then sheathed on the outer layer of the BN tube as a heating layer. The upper and lower openings are sealed with a perforated graphite gasket, and a molybdenum column is inserted into the hole as a conductive layer. The outer surface of the graphite layer is sealed with a zirconia tube as an insulation layer, and then placed in a regular octahedron made of magnesium oxide (MgO). The BN tube filled with the Se powder sample is assembled in a high-pressure synthesis assembly block and placed in an octahedral press for subsequent high-temperature and high-pressure reactions;

[0047] S2: High temperature and high pressure reaction preparation:

[0048] First, the pressure was increased gradually: the pressure was increased to 0.5 GPa within 30 min, and then increased to 5 GPa within 120 min. The total time of the gradient increase was 150 min.

[0049] Then, the temperature was increased gradually: the temperature was increased to 170°C within 10 min, the temperature was increased to 580°C within 10 min, and the temperature was increased to 650°C within 10 min. The total time of the gradient temperature increase was 30 min.

[0050] The reaction was carried out at 650°C and 5 GPa for 30 minutes, and then quenched. The pressure was released to normal pressure within 150 minutes at a controlled rate while cooling naturally to obtain Se crystals.

[0051] Example 2

[0052] This embodiment provides a method for synthesizing Se crystals under high temperature and high pressure. The difference from embodiment 1 is that in S2, the high temperature and high pressure reaction conditions are as follows:

[0053] First, the pressure was increased gradually: the pressure was increased to 0.5 GPa within 30 min, and then increased to 5 GPa within 120 min. The total time of the gradient increase was 150 min.

[0054] Then increase the temperature in a gradient manner: increase the temperature to 170°C within 10 minutes, then increase the temperature to 580°C within 10 minutes, and finally increase the temperature to 670°C within 10 minutes. The total time for the gradient temperature increase is 30 minutes.

[0055] The reaction was carried out at 670°C and 5 GPa for 30 minutes. After the reaction, the reaction was quenched and the pressure was released to normal pressure within 150 minutes while cooling naturally to obtain Se crystals.

[0056] Example 3

[0057] This embodiment provides a method for synthesizing Se crystals under high temperature and high pressure. The difference from embodiment 1 is that in S2, the high temperature and high pressure reaction conditions are as follows:

[0058] First, the pressure was increased gradually: the pressure was increased to 0.5 GPa within 30 min, and then increased to 5 GPa within 120 min. The total time of the gradient increase was 150 min.

[0059] Then, the temperature was increased gradually: the temperature was increased to 170°C within 10 min, the temperature was increased to 580°C within 10 min, and the temperature was increased to 700°C within 10 min. The total time of the gradient temperature increase was 30 min.

[0060] The reaction was carried out at 700°C and 5 GPa for 30 minutes. After the reaction, the reaction was quenched and the pressure was released to normal pressure within 150 minutes under a controlled pressure release rate while naturally cooling to obtain Se crystals.

[0061] Example 4

[0062] This embodiment provides a method for synthesizing Se crystals under high temperature and high pressure. The difference from embodiment 1 is that in S2, the high temperature and high pressure reaction conditions are as follows:

[0063] First, the pressure was increased gradually: the pressure was increased to 0.5 GPa within 40 min, and then increased to 5.2 GPa within 110 min. The total time of the gradient increase was 150 min.

[0064] Then, the temperature was increased gradually: the temperature was increased to 170°C within 10 min, the temperature was increased to 600°C within 10 min, and the temperature was increased to 650°C within 10 min. The total time of the gradient temperature increase was 30 min.

[0065] The reaction was carried out at 650°C and 5.2 GPa for 30 minutes. After the reaction, the reaction was quenched and the pressure was released to normal pressure within 150 minutes while cooling naturally to obtain Se crystals.

[0066] Example 5

[0067] This embodiment provides a method for synthesizing Se crystals under high temperature and high pressure. The difference from embodiment 1 is that in S2, the high temperature and high pressure reaction conditions are as follows:

[0068] First, the pressure was increased gradually: to 0.6 GPa within 35 min, and then to 4.8 GPa within 115 min. The total time for the gradient increase was 150 min.

[0069] Then increase the temperature gradually: increase the temperature to 170°C within 10 minutes, then increase the temperature to 500°C within 10 minutes, and finally increase the temperature to 650°C within 10 minutes. The total time of the gradient temperature increase is 30 minutes.

[0070] The reaction was carried out at 650°C and 5 GPa for 30 minutes, and then quenched. The pressure was released to normal pressure within 150 minutes at a controlled rate while cooling naturally to obtain Se crystals.

[0071] Comparative Example 1

[0072] The difference between the preparation method provided in this comparative example and that in Example 1 is that in S2, the high temperature and high pressure reaction conditions are as follows:

[0073] First, the pressure was increased gradually: the pressure was increased to 0.5 GPa within 30 min, and then increased to 3 GPa within 30 min. The total time of the gradient increase was 60 min.

[0074] Then, the temperature was increased gradually: the temperature was increased to 170°C within 10 min, the temperature was increased to 580°C within 10 min, and the temperature was increased to 900°C within 10 min. The total time of the gradient temperature increase was 30 min.

[0075] The reaction was carried out at 900°C and 3 GPa for 30 minutes. After the reaction, the mixture was quenched and the pressure was released to normal pressure within 150 minutes under a controlled rate while naturally cooling to obtain the product.

[0076] Comparative Example 2

[0077] The difference between the preparation method provided in this comparative example and that in Example 1 is that in S2, the high temperature and high pressure reaction conditions are as follows:

[0078] First, the pressure was increased gradually: the pressure was increased to 0.5 GPa within 30 min, and then increased to 5 GPa within 120 min. The total time of the gradient increase was 150 min.

[0079] Then increase the temperature in a gradient manner: increase the temperature to 170°C within 10 minutes, then increase the temperature to 580°C within 10 minutes, and finally increase the temperature to 760°C within 10 minutes. The total time for the gradient temperature increase is 30 minutes.

[0080] The reaction was carried out at 760° C. and 5 GPa for 30 minutes. After the reaction was completed, the product was quenched and the pressure release rate was controlled to be released to normal pressure within 150 minutes while naturally cooling to obtain the product.

[0081] Comparative Example 3

[0082] The difference between the preparation method provided in this comparative example and that in Example 1 is that in S2, the high temperature and high pressure reaction conditions are as follows:

[0083] First, the pressure was increased gradually: the pressure was increased to 0.5 GPa within 30 min, and then increased to 5 GPa within 120 min. The total time of the gradient increase was 150 min.

[0084] Gradient heating: raise the temperature to 170°C within 10 minutes, and then raise the temperature to 360°C within 20 minutes. The total time of gradient heating is 30 minutes.

[0085] The reaction was carried out at 360° C. and 5 GPa for 30 minutes. After the reaction, the product was quenched and the pressure was released to normal pressure within 150 minutes at a controlled rate while naturally cooling.

[0086] Comparative Example 4

[0087] The difference between the preparation method provided in this comparative example and that in Example 1 is that in S2, the high temperature and high pressure reaction conditions are as follows:

[0088] First, the pressure was increased gradually: the pressure was increased to 0.5 GPa within 30 min, and then increased to 5 GPa within 120 min. The total time of the gradient increase was 150 min.

[0089] Then, the temperature was increased gradually: the temperature was increased to 170°C within 10 min, and then to 570°C within 20 min. The total time of the gradient temperature increase was 30 min.

[0090] The reaction was carried out at 570° C. and 5 GPa for 30 minutes. After the reaction was completed, the reaction was quenched and the pressure was released to normal pressure within 150 minutes while cooling naturally to obtain the product.

[0091] Comparative Example 5

[0092] The difference between the preparation method provided in this comparative example and that in Example 1 is that in S2, the high temperature and high pressure reaction conditions are as follows:

[0093] First, the pressure was increased gradually: the pressure was increased to 0.5 GPa within 30 min, and then increased to 5 GPa within 120 min. The total time of the gradient increase was 150 min.

[0094] Then increase the temperature at a uniform rate: to 650°C within 30 minutes;

[0095] The reaction was carried out at 650° C. and 5 GPa for 30 minutes. After the reaction, the product was quenched and the pressure was released to normal pressure within 150 minutes at a controlled rate while naturally cooling.

[0096] Comparative Example 6

[0097] The preparation method provided in this comparative example is different from that in Example 1 in that, in S2, the reaction is carried out at 650° C. and 5 GPa for 20 minutes, and the other steps and parameters remain the same.

[0098] The high temperature and high pressure reaction conditions of Examples 1 to 5 and Comparative Examples 1 to 5 are summarized in Table 1.

[0099] Table 1

[0100]

[0101]

[0102] The products prepared in Examples 1 to 5 and Comparative Examples 1 to 6 were subjected to characterization tests, and the test results are summarized in Table 2.

[0103] Table 2

[0104]

[0105]

[0106] The test results of the product prepared in Example 1 are as follows: Figures 1-4 As shown:

[0107] Figure 1 This is a scanning electron microscope image of the product (Se crystal) prepared in Example 1, showing that the grown Se is a single crystal.

[0108] Figure 2 This is the Raman image of the product (Se crystal) prepared in Example 1, at 118 cm- 1 and 138cm- 1 There are obvious Raman peaks at the two locations, corresponding to the vibration peaks of Se.

[0109] Figure 3 The product (Se crystal) prepared in Example 1 has a peak at 236 cm- 1 Polarized Raman characteristics under vertical light incidence conditions; Figure 4 The product (Se crystal) prepared in Example 1 has a peak at 236 cm- 1 Polarized Raman characteristics under parallel light incident conditions at Figure 3 and Figure 4 It can be seen that the polarized Raman spectrum presents a four-petal shape, indicating that the grown Se has polarization characteristics, which is consistent with the theoretical prediction; the above Raman test proves that the product structure is a hexagonal crystal system.

[0110] The product test results in Comparative Example 2 are as follows Figure 5 As shown:

[0111] Figure 5 The Raman image of the product prepared in Comparative Example 2 is at 242 cm- 1There is an obvious Raman peak at the position where the product is grown. The Raman peak of the product prepared in Example 1 is different. Under this temperature and pressure, the structure changes and the grown product is glassy Se.

[0112] It can be seen from the above test results that Example 1-Example 5 adopts the method of first gradient pressure increase and then gradient temperature increase to the reaction temperature and pressure to carry out high-pressure and high-temperature reaction, and staged pressure increase (0.5GPa→5GPa) can reduce stress concentration, prevent selenium crystals from producing defects (such as dislocations or cracks) due to sudden pressure changes, improve crystallization integrity, and slowly increase pressure (total time 150min) is conducive to the orderly arrangement of selenium atoms, forming a more uniform crystal nucleus, and improving crystal quality and size. On the other hand, the purpose of using the method of gradient pressure increase is to protect the experimental equipment and ensure that the experiment is carried out normally. Too fast a pressure increase may cause the secondary anvil to rupture; it may undergo multiple phase changes during the heating process, and staged temperature increase (100℃→550℃→650℃) ensures that the phase change is carried out step by step to avoid non-equilibrium phase residue. The final product Se crystal size is large and the morphology is complete, all of which are hexagonal systems with stable product quality.

[0113] Comparing Example 1 with Comparative Example 1, when the reaction temperature is too high and the reaction pressure is too low, even if the gradient pressure and temperature increase method is adopted, it is difficult to grow the product to obtain Se single crystal, which is mainly composed of glassy Se.

[0114] Comparing Example 1 with Comparative Examples 2 to 4, in Comparative Example 2, the temperature was raised to 760°C to determine the temperature at which Se single crystals and unformed Se could be grown. At this point, the product was glassy Se, indicating that the reaction temperature had exceeded the optimum temperature. In Comparative Example 3, the temperature was lowered to observe whether Se single crystals could be grown at 360°C. It was found that crystals were difficult to grow at this temperature. In Comparative Example 4, the temperature was raised to 570°C, which was slightly lower than the optimum temperature. Although Se crystals were produced at this temperature, the crystals were small in size and fragmented, failing to meet the requirements.

[0115] Comparing Example 1 with Comparative Example 5, in Comparative Example 5, the temperature was raised to 650°C at a uniform rate during the heating stage. Since Se undergoes multiple phase transitions during the heating process, direct heating results in residual non-equilibrium phases, and the product contains a mixture of hexagonal and glassy phases.

[0116] Comparing Example 1 and Comparative Example 6, when the heat preservation and pressure holding time is too short, the crystal growth is incomplete, resulting in a smaller crystal size.

[0117] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0118] The above disclosures are only a few specific embodiments of the present invention. However, the embodiments of the present invention are not limited thereto. Any changes that can be conceived by those skilled in the art should fall within the scope of protection of the present invention.

Claims

1. A method for synthesizing Se crystals at high temperature and high pressure, characterized in that: The following steps are involved: Se powder is used as the starting material and placed in a sealed environment. The pressure is first gradually increased to 4.8-5.2 GPa, and then the temperature is gradually increased to 650-700°C. The reaction is maintained at this temperature and pressure for 25-35 minutes, and then quenched, cooled and decompressed to room temperature and normal pressure to obtain Se crystals.

2. The method for synthesizing Se crystals at high temperature and high pressure according to claim 1, characterized in that: The gradient pressure increase includes: increasing the pressure to 0.5-0.6 GPa within 30-40 minutes, and then increasing the pressure to 4.8-5.2 GPa within 110-120 minutes. The total time of the gradient pressure increase is 140-160 minutes.

3. The method for synthesizing Se crystals at high temperature and high pressure according to claim 2, characterized in that: The gradient pressure increase includes: increasing the pressure to 0.5 GPa within 30 minutes, and then increasing the pressure to 5 GPa within 120 minutes. The total time of the gradient pressure increase is 150 minutes.

4. The method for synthesizing Se crystals at high temperature and high pressure according to claim 1, characterized in that: The gradient heating includes: heating to 150-180° C. within 8-12 minutes, then heating to 500-600° C. within 8-12 minutes, and finally heating to 650-700° C. within 8-12 minutes. The total time of the gradient heating is 24-36 minutes.

5. The method for synthesizing Se crystals at high temperature and high pressure according to claim 4, characterized in that: The gradient heating includes: heating to 170° C. within 10 minutes, heating to 580° C. within 10 minutes, and finally heating to 650° C. within 10 minutes. The total time of the gradient heating is 30 minutes.

6. The method for synthesizing Se crystals at high temperature and high pressure according to claim 1, characterized in that: The pressure relief time is 150-200 minutes.

7. The method for synthesizing Se crystals at high temperature and high pressure according to claim 1, characterized in that: Before the reaction, the Se powder was pressed into a cylindrical shape with a height of 3.2 mm and a diameter of 3.5 mm as a sample, and placed in a BN tube.

8. The method for synthesizing Se crystals at high temperature and high pressure according to claim 1, characterized in that: The sealed environment includes an octahedral high-pressure device that can provide high-temperature and high-pressure reaction conditions. The octahedral high-pressure device contains a high-pressure synthesis assembly block, and the BN tube filled with Se powder is assembled in the high-pressure synthesis assembly block.

9. The method for synthesizing Se crystals at high temperature and high pressure according to claim 8, characterized in that: The assembly method of the BN tube filled with Se powder in the high-pressure synthesis assembly block includes: sealing the upper and lower openings of the BN tube filled with Se powder with BN discs, then sheathing a layer of graphite tube on the outer layer of the BN tube as a heating layer, sealing the upper and lower openings with a graphite gasket with a hole, inserting a molybdenum column into the hole as a conductive layer, and sealing the outside of the graphite layer with a layer of zirconia tube as a thermal insulation layer.

10. The method for synthesizing Se crystals at high temperature and high pressure according to claim 1, characterized in that: The size of the Se crystal is ≥500 μm, the crystal is off-white, the surface coating is brown, and the synthesized Se crystal is a hexagonal crystal system.

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