Synthesis container and synthesis method of selenium-barium compound polycrystal

Abstract

The invention belongs to the field of preparation of selenium-barium compound crystal materials, and provides a synthesis container and a synthesis method of selenium-barium compound polycrystals. The synthesis container comprises a quartz tube and a graphite crucible with a cover, the graphite crucible is composed of a crucible body and a crucible cover, one side of the crucible cover is provided with an external thread, the other side of the crucible cover is provided with a breather pipe penetrating through the crucible cover, the open end of the crucible body is provided with an internal thread, and when the synthesis container is in a working state, the quartz tube is a round tube with two closed ends; the graphite crucible with the cover is located in the quartz tube, and the bottom of the crucible body is located at one end of the quartz tube. When the synthesis container is used for preparing selenium-barium compound polycrystals, elemental Se is placed on the crucible cover on the outer side of the crucible body, elemental Ba and Ga (or elemental Ba, Ga and Ge) are placed in the crucible body, and a synthesis reaction is carried out in a two-area heating tube furnace. According to the method, the corrosion degree of the selenium-barium compound polycrystal to the quartz ampoule in the synthesis process can be effectively reduced, and the selenium-barium compound polycrystal which is single in chemical structure and free of impurity peaks is prepared.

Description

Technical Field

[0001] The invention belongs to the field of preparation of barium selenide compound crystal materials and relates to a synthesis container and a synthesis method of barium selenide compound polycrystals. Background Art

[0002] BaGa4Se7 and BaGa2GeSe6 are new infrared nonlinear optical materials with excellent performance. Among them, BaGa4Se7 has a large band gap (2.64eV), a wide transmission range (0.47~18μm), and a large nonlinear coefficient (d 22 =24.3pm / V,d 23 =20.4pm / V), moderate birefringence (Δn=0.06@2μm), high laser damage threshold (about 3.6 times that of AgGaS2), and can be pumped by 1-3μm laser to generate widely tunable infrared laser up to 18μm.

[0003] Wang et al. synthesized BaGa4Se7 in a single-temperature zone using a graphene-coated quartz ampoule (see WANGZ, WU H, MAO M, et al. Growth and optical properties of infrared nonlinear optical crystal BaGa4Se7 [J]. Optik, 2022, 252). The method involved coating the inner surface of the quartz ampoule with a graphite layer to prevent corrosion caused by Ba reacting with the ampoule. The synthesis furnace used was a single-temperature zone furnace. The reactants were high-purity elemental Ga(5N), Se(5N), and Ba(2N). The reactants were placed in the graphene-coated quartz ampoule and reacted at a low temperature of 450-480°C for 12-24 hours to allow Ga and Se to react fully. The reaction was then continued at a high temperature of 1060°C for 4 hours to allow Ba to fully participate in the reaction. Temperature and mechanical oscillation were then used to homogenize the polycrystals. This method carries the risk of explosion of the quartz ampoule due to the vigorous reaction between Ba and Se.

[0004] The synthesis of common compounds typically uses quartz ampoules as the synthesis container. Because barium easily reacts with quartz, causing corrosion and increasing the risk of explosion, pyrolytic boron nitride (PBN) is often added to the quartz tube or a graphite crucible is used when synthesizing compounds containing barium to prevent the reaction of Ba with quartz. Furthermore, the synthesis of barium selenide compounds is highly reactive, and intermediate products can even corrode the crucible. This not only exposes the barium to the quartz ampoule, potentially causing explosion and complicating safety, but also easily leads to problems such as incomplete reaction and compositional segregation in the synthesized polycrystals. Therefore, when synthesizing barium selenide compounds, consideration should be given to avoiding direct contact between elemental Se and elemental Ba to prevent corrosion reactions.

[0005] Li et al. synthesized BaGa4Se7 using a high-pressure synthesis method (see LI C, LI Z, SUNM, et al. High-pressure synthesis, growth and characterization of large-size BaGa4Se7 crystals [J]. Journal of Crystal Growth, 2022, 577). The specific method involves placing the elemental raw materials Ba (3N, solid), Ga (8N, liquid), and Se (6N, powder) at the bottom of a carbon-coated quartz ampoule. The ampoule is then placed in a synthesis furnace, and 3 atm of argon is introduced into the furnace through a vent pipe to balance the vapor pressure of Se at high temperatures. This method reduces the risk of explosion caused by the excessive saturated vapor pressure of Se. However, because it does not effectively separate Ba from Se, the violent reaction of the selenium-barium compound under high temperature and high pressure still poses a safety hazard, causing corrosion to the quartz ampoule. Furthermore, this method requires high equipment costs and precise control of the pressure and temperature fields, which presents certain technical difficulties.

[0006] Guo et al. used a dual-temperature zone vapor transport synthesis method to synthesize more than 300g of BaGa4Se7 polycrystals in a single batch (see GUOY, LI Z, LEI Z, et al. Synthesis, Growth of Crack-Free Large-Size BaGa4Se7 Crystal, and Annealing Studies [J]. Crystal Growth & Design, 2019, 19 (2): 1282-7.). The specific method is: according to the stoichiometric ratio, high-purity Ba (3N), Ga (8N), and Se (6N) are placed in a long quartz tube, where Ba and Ga are located in a PBN crucible in the high-temperature zone, and Se is located in a quartz tube in the low-temperature zone. Because this method places the synthetic raw material Se in the synthesis system cavity, which is large, it is easy to cause composition segregation of the synthetic product, affecting the quality of the subsequent single crystal growth. Summary of the Invention

[0007] In response to the problems of the existing methods for synthesizing barium selenide compound polycrystals, such as the violent reaction between Ba and Se, which easily leads to corrosion of the quartz ampoule and the risk of explosion, as well as the composition segregation of the synthetic products, the present invention provides a synthesis container and a synthesis method for barium selenide compound polycrystals, so as to effectively reduce the degree of corrosion of the quartz ampoule during the synthesis process of barium selenide compound polycrystals, and prepare barium selenide compound polycrystals with a single chemical structure and no impurity peaks, thereby meeting the needs of single crystal growth.

[0008] The technical concept of the present invention is as follows: To prevent corrosion of the quartz tube caused by the violent reaction of Ba and Se, a covered graphite crucible is designed inside the quartz tube. The covered graphite crucible consists of a crucible lid and a crucible body. A vent pipe is provided on the crucible lid and passes through the crucible lid. Elemental Se is placed on the crucible lid outside the crucible body, and elemental Ba and elemental Ga (when synthesizing BaGa4Se7 polycrystals), or elemental Ba, elemental Ga, and elemental Ge (when synthesizing BaGa2GeSe6 polycrystals), are placed inside the crucible body. The crucible lid separates elemental Ba from solid elemental Se. During the synthesis process, elemental Se is continuously transported into the crucible body in the form of Se vapor through the vent pipe, thereby preventing the violent reaction of Ba and Se at high temperatures, thereby reducing corrosion to the quartz tube and preventing the quartz tube from exploding. The present invention also conducts the synthesis reaction in a two-zone heating tubular furnace, positioning the crucible containing elemental Ba, elemental Ga, and elemental Ge, or the region containing elemental Ba and elemental Ga, in the second temperature zone, which is relatively higher, while positioning the region containing elemental Se in the quartz tube, which is relatively lower, in the first temperature zone. This reduces the saturated vapor pressure of Se and helps avoid quartz tube explosion. This allows the preparation of polycrystals of a barium selenide compound with a single chemical structure and no impurity peaks, while ensuring the safety of the synthesis process.

[0009] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is as follows:

[0010] A synthesis container for barium selenide compound polycrystals includes a quartz tube and a graphite crucible with a lid. The graphite crucible with a lid consists of a crucible body and a crucible lid. The crucible lid has an external thread on one side and a vent pipe penetrating the crucible lid on the other side. The open end of the crucible body has an internal thread. The length of the vent pipe on the crucible lid is 0.15 to 0.40 times the length of the crucible body. The external thread on the crucible lid matches the internal thread on the crucible body.

[0011] When the synthesis container is in the initial state, the quartz tube is a circular tube with one end open and the other end closed; when the synthesis container is in the working state, the quartz tube is a circular tube with both ends closed, the graphite crucible with a cover is located in the quartz tube, and the bottom of the crucible body is located at one end of the quartz tube; the length of the crucible body is 0.6 to 0.7 times the length of the quartz tube with both ends in the closed state.

[0012] In the technical solution of the synthesis container of the barium selenide compound polycrystal, the vent pipe on the crucible cover is preferably arranged perpendicular to the crucible cover.

[0013] In the technical solution of the synthesis container of the barium selenide compound polycrystal, the inner diameter of the vent tube is preferably 0.3 to 0.4 times the inner diameter of the crucible.

[0014] In the technical solution for the synthesis vessel for barium selenide compound polycrystals, the outer diameter of the crucible body is 0.1 to 1 mm smaller than the inner diameter of the quartz tube, and the outer diameter of the crucible lid is 0.1 to 1 mm smaller than the inner diameter of the quartz tube. These dimensions facilitate assembly of the synthesis vessel and synthesis of barium selenide compound polycrystals. Typically, the outer diameter of the crucible lid is equal to or slightly larger than the outer diameter of the crucible body.

[0015] In the technical solution of the synthesis container of the barium selenide compound polycrystal, the ratio of the length to the inner diameter of the quartz tube with both ends in a closed state is preferably 1:(0.07-0.15).

[0016] Furthermore, in the technical solution of the synthesis container of the above-mentioned barium selenide compound polycrystal, the length and inner diameter of the quartz tube with both ends in a closed state can be adjusted according to the synthesis amount of the barium selenide compound polycrystal. From the perspective of ensuring safety, the quality of the synthesized barium selenide compound polycrystal and reducing costs, the length of the quartz tube with both ends in a closed state is preferably 350-400 mm, and the inner diameter is preferably 28-52.5 mm.

[0017] The present invention also provides a method for synthesizing a barium selenide compound polycrystal, wherein the barium selenide compound is BaGa4Se7 or BaGa2GeSe6. The method uses the above-mentioned synthesis container to synthesize the barium selenide compound polycrystal, and the steps are as follows:

[0018] S1. Cleaning, drying and assembly of synthesis containers

[0019] The crucible body, crucible cover and quartz tube in the initial state are cleaned and dried, the crucible cover is installed on the open end of the crucible body and placed in the quartz tube so that the closed end of the crucible body is located at the closed end of the quartz tube, a quartz exhaust pipe is connected to the open end of the quartz tube, and deionized water is injected into the quartz tube to clean it and dry it;

[0020] S2. Loading and sealing

[0021] In an argon atmosphere, elemental Ga and elemental Ge are added into the crucible through an exhaust pipe and a vent pipe, or elemental Ga is added into the crucible; then, in an argon atmosphere, elemental Se is placed on the crucible cover outside the crucible through an exhaust pipe; and then, in an argon atmosphere, elemental Ba is added into the crucible through an exhaust pipe and a vent pipe to complete the loading;

[0022] After the loading is completed, the quartz tube is vacuumed through the vacuum pipe until the pressure inside the quartz tube is ≤10 -4 The open end of the quartz tube is sealed at Pa;

[0023] S3. Synthesis

[0024] S301. Synthesis of a barium selenide compound polycrystal is performed in a two-zone heated tubular furnace comprising a first temperature zone and a second temperature zone. The two-zone heated tubular furnace is positioned horizontally. A synthesis vessel, after being loaded and sealed with a quartz tube, is placed horizontally within the two-zone heated tubular furnace, with the crucible containing elemental Ba, elemental Ga, and elemental Ge, or the area containing elemental Ba and elemental Ga, located in the second temperature zone, and the quartz tube containing elemental Se located in the first temperature zone. The two ends of the sealed quartz tube serve as temperature control points.

[0025] S302. The second temperature zone is heated to 250-300°C at a heating rate of 37.5-50°C / h and kept warm for 4-8h; then the second temperature zone is heated to 780-880°C at a heating rate of 35-62.5°C / h and kept warm for 8-12h; then the second temperature zone is heated to 1060-1080°C at a heating rate of 15-23.5°C / h and kept warm for 50-64h; when the second temperature zone is heated to 800°C, the first temperature zone is heated at a heating rate of 34.5-65 The first temperature zone is heated to 250-300°C at a heating rate of 65°C / h and kept at this temperature for 60-76h; the temperature of the first temperature zone is then heated to 1080-1120°C at a heating rate of 65-97.5°C / h and kept at this temperature for 45-52h; after the second temperature zone is kept at this temperature, the second temperature zone is subjected to at least two temperature oscillations between temperatures T1 and T2 while the first temperature zone is kept at 1080-1120°C, with T1 = 800-980°C and T2 = 1060-1080°C;

[0026] S303. After the temperature oscillation is completed, the second temperature zone is cooled first, firstly cooled to 800-850°C at a cooling rate of 32.5-43.5°C / h, and then cooled to room temperature at a cooling rate of 48.5-96.5°C / h; after the second temperature zone is cooled for 6-10h, the first temperature zone is cooled, firstly cooled to 800-900°C at a cooling rate of 33.5-50°C / h, and then cooled to room temperature at a cooling rate of 61-106.5°C / h to obtain a polycrystal of barium selenide compound.

[0027] In the technical solution of the above-mentioned method for synthesizing polycrystals of barium selenide compounds, when the barium selenide compound is BaGa4Se7, step S2 uses elemental Ba, elemental Se and elemental Ga as raw materials, and the molar ratio of the ingredients is Ba:Ga:Se=1:4:(7.07~7.14); when the barium selenide compound is BaGa2GeSe6, step S2 uses elemental Ba, elemental Se, elemental Ga and elemental Ge as raw materials, and the molar ratio of the ingredients is Ba:Ga:Ge:Se=1:2:(1.005~1.01):(6.06~6.12).

[0028] In the technical solution of the above-mentioned method for synthesizing barium selenide compound polycrystals, the amount of elemental Se added in step S2 should ensure that when step S2 is completed and the quartz tube is in a horizontal state, the solid elemental Se on the crucible cover does not contact the end of the vent tube.

[0029] In the technical solution of the above-mentioned method for synthesizing barium selenide compound polycrystals, the amount of elemental Ba and elemental Ga, or elemental Ba, elemental Ga and elemental Ge added in step S2 should ensure that after the loading of step S2 is completed, the total volume of the raw materials in the crucible body is 20% to 50% of the total volume of the crucible body.

[0030] Compared with the prior art, the technical solution provided by the present invention produces the following beneficial technical effects:

[0031] 1. The present invention provides a synthesis vessel for barium selenide compound polycrystals, comprising a quartz tube and a graphite crucible with a lid. The graphite crucible with a lid consists of a crucible body and a crucible lid. The crucible lid is provided with an external thread on one side and a vent pipe penetrating the crucible lid on the other side. The open end of the crucible body is provided with an internal thread. When the synthesis vessel is in an initial state, the quartz tube is a circular tube with one end open and the other end closed. When the synthesis vessel is in an operating state, the quartz tube is a circular tube with both ends closed. The graphite crucible with a lid is located in the quartz tube, and the bottom of the crucible body is located at one end of the quartz tube. The length of the crucible body is 0.6 to 0.7 times the length of the quartz tube with both ends closed. Based on this synthesis vessel, the present invention also provides a method for synthesizing barium selenide compound polycrystals. This method places elemental Se on a crucible lid outside the crucible body, places elemental Ba and elemental Ga (when synthesizing BaGa4Se7 polycrystals), or places elemental Ba, elemental Ga, and elemental Ge (when synthesizing BaGa2GeSe6 polycrystals) inside the crucible body, separates elemental Ba from solid elemental Se via the crucible lid, and transports elemental Se into the crucible body as Se vapor through a vent pipe during the synthesis process. This prevents a violent reaction between Ba and Se at high temperatures, thereby reducing corrosion to the quartz tube and preventing explosion of the quartz tube. The method of the present invention can improve the synthesis quality of barium selenide compound polycrystals while ensuring the safety of the synthesis process, providing raw material support for the growth of BaGa4Se7 single crystals or BaGa2GeSe6 single crystals.

[0032] 2. The method of the present invention performs a synthesis reaction in a two-zone heating tubular furnace, wherein the crucible contains elemental Ba, elemental Ga, and elemental Ge, or the area containing elemental Ba and elemental Ga is located in the second temperature zone with a relatively higher temperature, and the area containing elemental Se in the quartz tube is located in the first temperature zone with a relatively lower temperature, thereby reducing the saturated vapor pressure of Se, which is also beneficial for avoiding the explosion problem of the quartz tube.

[0033] 3. The present invention has confirmed through experiments that the chemical structure of BaGa4Se7 polycrystals and BaGa2GeSe6 polycrystals prepared by the method of the present invention is single and free of impurity peaks, and the single synthesis amount can reach 80 to 120 g. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the structure of the quartz tube in the initial state.

[0035] Figure 2 It is a structural diagram of the crucible body.

[0036] Figure 3 It is a structural diagram of the crucible cover.

[0037] Figure 4 yes Figure 3 Left view of .

[0038] Figure 5 This is a schematic diagram of the structure of the assembled synthesis container.

[0039] Figure 6 This is a photo of the composite container after assembly.

[0040] Figure 7 Schematic diagram of the structure of the synthesis container after loading in Example 2.

[0041] Figure 8 1 is a schematic diagram of the structure of the synthesis container after the loading and sealing of the quartz tube in Example 2. This figure is also a schematic diagram of the structure of the synthesis container in a working state.

[0042] Figure 9 This is a schematic diagram of the structure in which the synthesis container after the charging and sealing of the quartz tube in Example 2 is placed in a two-zone heating tube furnace.

[0043] Figure 10 This is a schematic diagram of Example 2 after the synthesis of BaGa4Se7 polycrystals is completed in a two-zone heating tube furnace.

[0044] Figure 11 This is a photo of the synthesis container after the synthesis of BaGa4Se7 polycrystals in Example 2 is completed.

[0045] Figure 12 This is a photograph of the BaGa4Se7 polycrystal synthesized in Example 2.

[0046] Figure 13 This is the X-ray diffraction pattern of the BaGa4Se7 polycrystal synthesized in Example 2.

[0047] Figure 14 This is a photograph of the BaGa2GeSe6 polycrystal synthesized in Example 3.

[0048] Figure 15 This is the X-ray diffraction pattern of the BaGa2GeSe6 polycrystal synthesized in Example 3.

[0049] In the figure, 1 is a quartz tube, 2 is a graphite crucible with a lid, 3 is a crucible body, 4 is a crucible lid, 5 is an external thread, 6 is a vent pipe, 7 is an internal thread, 8 is an exhaust pipe, 9 is elemental Ga, 10 is elemental Se, 11 is elemental Ba, 12 is the first temperature zone, 13 is the second temperature zone, 14 is a heating element, 15 is the furnace body of a two-zone heating tube furnace, 16 is a first temperature-controlled thermocouple, 17 is a second temperature-controlled thermocouple, and 18 is a BaGa4Se7 polycrystal. DETAILED DESCRIPTION

[0050] The following examples further illustrate the synthesis vessel and method for the barium selenide compound polycrystal provided by the present invention. It should be noted that the following examples are intended only to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by persons skilled in the art to the present invention based on the above-described disclosure are still within the scope of protection of the present invention.

[0051] Example 1

[0052] In this embodiment, a synthesis container for barium selenide compound polycrystals is provided.

[0053] The synthesis container of the barium selenide compound polycrystal consists of a quartz tube 1 and a graphite crucible 2 with a lid. The cross section of the quartz tube is circular. The graphite crucible 2 with a lid consists of a crucible body 3 and a crucible lid 4. The cross sections of the crucible body 3 and the crucible lid 4 are circular. One side of the crucible lid 4 is provided with an external thread 5 and the other side is provided with a vent pipe 6 that passes through the crucible lid. The vent pipe 6 is arranged perpendicular to the crucible lid 4. The open end of the crucible body 3 is provided with an internal thread 7. The external thread 5 on the crucible lid 4 matches the internal thread 7 of the crucible body 3. The structure of the crucible body is as follows: Figure 2 As shown, the structure of the crucible cover is as follows Figures 3-4 More specifically, the outer diameters of the crucible body 3 and the crucible cover 4 are equal, both being 29 mm, the inner diameter of the quartz tube is 30 mm, the length of the crucible body is 264.5 mm, the length of the vent tube 6 is 0.3 times the length of the crucible body 3, and the inner diameter of the vent tube 6 is 0.35 times the inner diameter of the crucible body 3.

[0054] When the synthesis container is in the initial state, the quartz tube 1 is a round tube with one end open and the other end closed. Figure 1 As shown, the length of the quartz tube 1 is greater than the length of the covered graphite crucible 2. When the synthesis container is in operation: the quartz tube 1 is a round tube with both ends closed, one end of the quartz tube is provided with a quartz hook, the covered graphite crucible 2 is located inside the quartz tube 1, and the bottom of the crucible body 3 is located at one end of the quartz tube 1; the length of the quartz tube 1 with both ends closed is 400mm, Figure 8 It is a schematic diagram of the structure of a synthesis container in working state, in which raw materials for preparing polycrystals of barium selenide compounds are loaded and the open end of the quartz tube is sealed.

[0055] Example 2

[0056] In this embodiment, a method for synthesizing BaGa4Se7 polycrystals is provided. The method uses the synthesis container described in Example 1 to synthesize BaGa4Se7 polycrystals, and the steps are as follows:

[0057] S1. Cleaning, drying and assembly of synthesis containers

[0058] Clean the crucible body 3, crucible cover 4 and the quartz tube 1 in its initial state (the quartz tube 1 is a round tube with one end open and the other end closed) with deionized water and a test tube brush, and then place them in a drying oven to dry. Install the dried crucible cover 4 on the open end of the crucible body 3 through the external thread 5 on the crucible cover and the internal thread 7 on the crucible body 3, then place the crucible body 3 with the crucible cover 4 installed in the quartz tube 1, so that the closed end of the crucible body 3 is located at the closed end of the quartz tube 1, even if the outer side of the closed end of the crucible body 3 is in contact with the inner side of the closed end of the quartz tube 1, and then connect a quartz exhaust pipe 8 to the open end of the quartz tube 1. Inject deionized water into the quartz tube 1 through the exhaust pipe 8 and pour it out completely after filling the quartz tube. Repeat this operation several times until it is clean and place it in a drying oven to dry. Figure 5 This is a schematic diagram of the structure of the assembled synthesis container. Figure 6 This is a photo of the composite container after assembly.

[0059] S2. Loading and sealing

[0060] BaGa4Se7 polycrystals were synthesized using elemental Ba(3N), elemental Se(6N) and elemental Ga(6N) as raw materials, with a molar ratio of Ba:Ga:Se = 1:4:7.07. Considering that part of Se cannot fully participate in the reaction in the actual reaction, an excess of 1% Se was weighed on the basis of the theoretical Se dosage (Ba:Ga:Se <molar ratio> = 1:4:7) during the preparation. Specifically, 11.9366 g of elemental Ba(3N), 24.24157 g of elemental Ga(6N) and 48.04297 g of elemental Se(6N) were weighed in an argon atmosphere.

[0061] In an argon atmosphere, a funnel is used to add elemental Ga (6N) into the crucible body 3 through the exhaust pipe 8 and the vent pipe 6; then, in an argon atmosphere, a funnel is used to place elemental Se (6N) on the crucible cover 4 outside the crucible body 3 through the exhaust pipe 8; and then, in an argon atmosphere, a funnel is used to add elemental Ba (3N) into the crucible body 3 through the exhaust pipe 8 and the vent pipe 6 to complete the loading. The structural diagram of the synthesis container after the loading is completed is shown in FIG. Figure 7 shown.

[0062] After the loading is completed, the quartz tube 1 is vacuumed through the vacuum pipe 8 until the pressure inside the quartz tube is ≤10 -4 Pa, then seal the open end of the quartz tube 1, and make a quartz hook at the sealed end of the quartz tube, and the sealed quartz tube is transformed into a quartz ampoule. After the above operation of this step, a synthetic container after the filling and sealing of the quartz tube is obtained, and its structural diagram is shown as follows Figure 8 As shown, this figure is also a structural schematic diagram of the synthesis container in working state.

[0063] S3. Synthesis

[0064] The synthesis of S301.BaGa4Se7 polycrystals was carried out in a two-zone heating tube furnace, such as Figure 9 As shown, the two-zone heating tube furnace includes a first temperature zone 12 and a second temperature zone 13, and the first temperature zone and the second temperature zone are provided with independent heating elements 14. The two-zone heating tube furnace is placed horizontally (that is, the furnace body 15 of the two-zone heating tube furnace is placed horizontally). The synthesis container after the loading and sealing of the quartz tube is placed horizontally in the two-zone heating tube furnace, so that the area in the crucible body containing elemental Ba (3N) and elemental Ga (6N) is located in the second temperature zone, and the area in the quartz tube containing elemental Se is located in the first temperature zone. The two ends of the sealed quartz tube are used as temperature control points, and a first temperature-controlling thermocouple 16 and a second temperature-controlling thermocouple 17 are respectively provided at the two ends of the sealed quartz tube.

[0065] S302. Heat the second temperature zone to 300℃ at a heating rate of 45.5℃ / h and keep it warm for 4h; then heat the second temperature zone to 800℃ at a heating rate of 62.5℃ / h and keep it warm for 12h; then heat the second temperature zone to 1060℃ at a heating rate of 16.5℃ / h and keep it warm for 64h; when the second temperature zone is heated to 800℃, start heating the first temperature zone, heating the first temperature zone to 300℃ at a heating rate of 45.5℃ / h and keep it warm for 74h; then heat the first temperature zone to 1080℃ at a heating rate of 97.5℃ / h and keep it warm for 52h; after the second temperature zone is kept at 1060℃, perform two temperature oscillations on the second temperature zone between 980℃ and 1060℃ while the first temperature zone is kept at 1080℃.

[0066] S303. After the temperature oscillation is completed, the second temperature zone is cooled down first, first at a cooling rate of 32.5℃ / h to 800℃, and then at a cooling rate of 64.5℃ / h to room temperature; after the second temperature zone is cooled down for 8 hours, the first temperature zone is cooled down, first at a cooling rate of 50℃ / h to 880℃, and then at a cooling rate of 64.5℃ / h to room temperature to obtain BaGa4Se7 polycrystal. The schematic diagram and photos of the BaGa4Se7 polycrystal after synthesis are shown in the following figure. Figure 10 、 11 shown.

[0067] The photo of the BaGa4Se7 polycrystal synthesized in this embodiment is shown in FIG. Figure 12 Its X-ray diffraction pattern is shown as Figure 13 As shown by Figure 13 It can be seen that the chemical structure of the BaGa4Se7 polycrystal synthesized in this example is single and has no impurity peaks.

[0068] Example 3

[0069] In this embodiment, a method for synthesizing BaGa2GeSe6 polycrystals is provided. The method uses the synthesis container described in Example 1 to synthesize BaGa2GeSe6 polycrystals, and the steps are as follows:

[0070] S1. Cleaning, drying and assembly of synthesis containers

[0071] Clean the crucible body 3, crucible cover 4 and the quartz tube 1 in its initial state (the quartz tube 1 is a round tube with one end open and the other end closed) with deionized water and a test tube brush, and then place them in a drying oven to dry. Install the dried crucible cover 4 on the open end of the crucible body 3 through the external thread 5 on the crucible cover and the internal thread 7 on the crucible body 3, then place the crucible body 3 with the crucible cover 4 installed in the quartz tube 1, so that the closed end of the crucible body 3 is located at the closed end of the quartz tube 1, even if the outer side of the closed end of the crucible body 3 is in contact with the inner side of the closed end of the quartz tube 1, and then connect a quartz exhaust pipe 8 to the open end of the quartz tube 1. Inject deionized water into the quartz tube 1 through the exhaust pipe 8 and pour it out completely after filling the quartz tube. Repeat this operation several times until it is clean and place it in a drying oven to dry. Figure 5 This is a schematic diagram of the structure of the assembled synthesis container. Figure 6 This is a photo of the composite container after assembly.

[0072] S2. Loading and sealing

[0073] BaGa2GeSe6 polycrystals were synthesized using elemental Ba(3N), elemental Se(6N), elemental Ga(6N) and elemental Ge(6N) as raw materials, with a molar ratio of Ba:Ga:Ge:Se=1:2:1.005:6.06. Considering that part of Ge and Se cannot fully participate in the reaction in the actual reaction, an excess of 0.5% Ge and 1% Se were weighed on the basis of the theoretical amount of Ge and Se (Ba:Ga:Ge:Se<molar ratio>=1:2:1:6) when preparing the ingredients. Specifically, 13.3462g of elemental Ba(3N), 13.55220g of elemental Ga(6N), 7.09485g of elemental Ge(6N) and 46.50326g of elemental Se(6N) were weighed in an argon atmosphere.

[0074] In an argon atmosphere, a funnel is used to add elemental Ga (6N) and elemental Ge (6N) into the crucible body 3 through the exhaust pipe 8 and the vent pipe 6; then, in an argon atmosphere, a funnel is used to place elemental Se (6N) on the crucible cover 4 outside the crucible body 3 through the exhaust pipe 8; and then, in an argon atmosphere, a funnel is used to add elemental Ba (3N) into the crucible body 3 through the exhaust pipe 8 and the vent pipe 6 to complete the loading.

[0075] After the loading is completed, the quartz tube 1 is vacuumed through the vacuum pipe 8 until the pressure inside the quartz tube is ≤10 -4 After that, the open end of the quartz tube 1 is sealed, and a quartz hook is made at the sealed end of the quartz tube. The sealed quartz tube is then transformed into a quartz ampoule. After the above-mentioned operation of this step, a synthetic container after the charging and sealing of the quartz tube is obtained.

[0076] S3. Synthesis

[0077] S301. The synthesis of BaGa2GeSe6 polycrystals is carried out in a two-zone heating tube furnace, which includes a first temperature zone 12 and a second temperature zone 13. The first temperature zone and the second temperature zone are provided with independent heating elements 14. The two-zone heating tube furnace is placed horizontally (that is, the furnace body 15 of the two-zone heating tube furnace is placed horizontally). The synthesis container after the loading and sealing of the quartz tube is placed horizontally in the two-zone heating tube furnace, so that the area in the crucible body containing elemental Ba (3N), elemental Ga (6N) and elemental Ge (6N) is located in the second temperature zone, and the area in the quartz tube containing elemental Se is located in the first temperature zone. The two ends of the sealed quartz tube are used as temperature control points, and a first temperature-controlled thermocouple 16 and a second temperature-controlled thermocouple 17 are respectively provided at the two ends of the sealed quartz tube.

[0078] S302. Heat the second temperature zone to 300℃ at a heating rate of 45.5℃ / h and keep it warm for 4h; then heat the second temperature zone to 800℃ at a heating rate of 62.5℃ / h and keep it warm for 12h; then heat the second temperature zone to 1060℃ at a heating rate of 16.5℃ / h and keep it warm for 64h; when the second temperature zone is heated to 800℃, start heating the first temperature zone, heating the first temperature zone to 300℃ at a heating rate of 45.5℃ / h and keep it warm for 74h; then heat the first temperature zone to 1080℃ at a heating rate of 97.5℃ / h and keep it warm for 52h; after the second temperature zone is kept at 1060℃, perform two temperature oscillations on the second temperature zone between 800℃ and 1060℃ while the first temperature zone is kept at 1080℃.

[0079] S303. After the temperature oscillation is completed, the second temperature zone is cooled first, firstly cooled to 800°C at a cooling rate of 32.5°C / h, and then cooled to room temperature at a cooling rate of 64.5°C / h; after the second temperature zone is cooled for 8h, the first temperature zone is cooled, firstly cooled to 880°C at a cooling rate of 50°C / h, and then cooled to room temperature at a cooling rate of 106.5°C / h to obtain BaGa2GeSe6 polycrystals.

[0080] The photo of the BaGa2GeSe6 polycrystal synthesized in this embodiment is shown in FIG. Figure 14 Its X-ray diffraction pattern is shown as Figure 15 As shown by Figure 15 It can be seen that the chemical structure of the BaGa2GeSe6 polycrystal synthesized in this embodiment is single and has no impurity peaks.

Claims

1. A synthesis container for barium selenide compound polycrystals, comprising a quartz tube (1), characterized in that: It also includes a graphite crucible (2) with a cover, the graphite crucible (2) with a cover consists of a crucible body (3) and a crucible cover (4), one side of the crucible cover (4) is provided with an external thread (5), and the other side is provided with a vent pipe (6) passing through the crucible cover, the open end of the crucible body (2) is provided with an internal thread (7), the length of the vent pipe (6) on the crucible cover (4) is 0.15 to 0.4 times the length of the crucible body (3), and the external thread (5) on the crucible cover (4) and the internal thread (7) of the crucible body (3) match each other; When the synthesis container is in an initial state, the quartz tube (1) is a circular tube with one end open and the other end closed; when the synthesis container is in a working state, the quartz tube (1) is a circular tube with both ends closed, the graphite crucible (2) with a cover is located in the quartz tube (1), and the bottom of the crucible body (3) is located at one end of the quartz tube (1); the length of the crucible body (3) is 0.6 to 0.7 times the length of the quartz tube (1) with both ends in a closed state.

2. The synthesis container of barium selenide compound polycrystal according to claim 1, characterized in that: The vent pipe (6) on the crucible cover (4) is arranged perpendicular to the crucible cover (4).

3. The synthesis container of barium selenide compound polycrystal according to claim 1, characterized in that: The inner diameter of the vent pipe (6) is 0.3 to 0.4 times the inner diameter of the crucible body (3).

4. The synthesis container for barium selenide compound polycrystal according to claim 1, characterized in that: The outer diameter of the crucible body (3) is 0.1 to 1 mm smaller than the inner diameter of the quartz tube (1), and the outer diameter of the crucible cover (4) is 0.1 to 1 mm smaller than the inner diameter of the quartz tube (1).

5. The synthesis container for barium selenide compound polycrystal according to any one of claims 1 to 4, characterized in that: The ratio of the length to the inner diameter of the quartz tube (1) with both ends in a closed state is 1:(0.07-0.15).

6. A method for synthesizing a polycrystalline barium selenide compound, characterized in that: The barium selenide compound is BaGa4Se7 or BaGa2GeSe6. The method uses the synthesis container according to any one of claims 1 to 5 to synthesize the barium selenide compound polycrystal, and the steps are as follows: S1. Cleaning, drying and assembly of synthesis containers The crucible body (3), the crucible cover (4) and the quartz tube (1) in the initial state are cleaned and dried, the crucible cover (4) is installed on the open end of the crucible body (3) and placed in the quartz tube (1), so that the closed end of the crucible body (3) is located at the closed end of the quartz tube (1), a quartz exhaust pipe (8) is connected to the open end of the quartz tube (1), and deionized water is injected into the quartz tube (1) to clean and dry it; S2. Loading and sealing In an argon atmosphere, elemental Ga and elemental Ge are added into the crucible body (3) through an exhaust pipe (8) and a vent pipe (6), or elemental Ga is added into the crucible body (3); then, in an argon atmosphere, elemental Se is placed on the crucible cover (4) outside the crucible body (3) through an exhaust pipe (8); and then, in an argon atmosphere, elemental Ba is added into the crucible body through an exhaust pipe (8) and a vent pipe (6), thereby completing the loading; After the loading is completed, the quartz tube (1) is vacuumed through the vacuum pipe (8) until the pressure inside the quartz tube is ≤10 -4 The open end of the quartz tube (1) is sealed at Pa; S3. Synthesis S301. Synthesis of a barium selenide compound polycrystal is performed in a two-zone heated tubular furnace comprising a first temperature zone and a second temperature zone. The two-zone heated tubular furnace is positioned horizontally. A synthesis vessel, after being loaded and sealed with a quartz tube, is placed horizontally within the two-zone heated tubular furnace, with the crucible containing elemental Ba, elemental Ga, and elemental Ge, or the area containing elemental Ba and elemental Ga, located in the second temperature zone, and the quartz tube containing elemental Se located in the first temperature zone. The two ends of the sealed quartz tube serve as temperature control points. S302. Heat the second temperature zone to 250-300℃ at a heating rate of 37.5-50℃ / h and keep warm for 4-8 hours; then heat the second temperature zone to 780-880℃ at a heating rate of 35-62.5℃ / h and keep warm for 8-12 hours. h; then raise the temperature of the second temperature zone to 1060~1080℃ at a heating rate of 15~23.5℃ / h and keep it warm for 50~64h; when the second temperature zone rises to 800℃, start heating the first temperature zone, raise the temperature of the first temperature zone to 250~300℃ at a heating rate of 34.5~65℃ / h, and keep it warm for 60~76h; then raise the temperature of the first temperature zone to 1080~1120℃ at a heating rate of 65~97.5℃ / h and keep it warm for 45~52h; after the second temperature zone is kept warm, perform temperature oscillation between temperatures T1 and T2 for at least 2 times in the second temperature zone while the first temperature zone is kept warm at 1080~1120℃, with T1=800~980℃ and T2=1060~1080℃; S303. After the temperature oscillation is completed, the second temperature zone is cooled first, firstly cooled to 800~850℃ at a cooling rate of 32.5~43.5℃ / h, and then cooled to room temperature at a cooling rate of 48.5~96.5℃ / h; after the second temperature zone is cooled for 6~10h, the first temperature zone is cooled, firstly cooled to 800~900℃ at a cooling rate of 33.5~50℃ / h, and then cooled to room temperature at a cooling rate of 61~106.5℃ / h to obtain a polycrystal of barium selenide compound.

7. The method for synthesizing a polycrystal of a barium selenide compound according to claim 6, wherein: When the barium selenide compound is BaGa4Se7, step S2 uses elemental Ba, elemental Se and elemental Ga as raw materials, and the molar ratio of the ingredients is Ba:Ga:Se=1:4:(7.07~7.14); when the barium selenide compound is BaGa2GeSe6, step S2 uses elemental Ba, elemental Se, elemental Ga and elemental Ge as raw materials, and the molar ratio of the ingredients is Ba:Ga:Ge:Se=1:2:(1.005~1.01):(6.06~6.12).

8. The method for synthesizing a polycrystal of a barium selenide compound according to claim 6 or 7, characterized in that: The amount of elemental Se added in step S2 should ensure that when step S2 is completed and the quartz tube is in a horizontal state, the solid elemental Se on the crucible cover does not contact the end of the vent tube.

9. The method for synthesizing a polycrystal of a barium selenide compound according to claim 6 or 7, characterized in that: In step S2, the amount of elemental Ba and elemental Ga, or elemental Ba, elemental Ga and elemental Ge added should ensure that after the loading in step S2 is completed, the total volume of the raw materials in the crucible is 20% to 50% of the total volume of the crucible.

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