Selenium-gallium-barium single crystal and growth method thereof

Abstract

The invention discloses a selenium gallium barium single crystal and a growth method thereof. The growth method of the selenium-gallium-barium single crystal comprises the following steps: placing a crucible containing BaGa4Se7 seed crystals and BaGa4Se7 polycrystals in a quartz tube, vacuumizing the quartz tube, filling argon into the quartz tube, and sealing the quartz tube in a melting manner; the quartz tube is placed in a crystal growth furnace, and the crystal growth furnace is vertically provided with a high-temperature area, a gradient cooling area and a low-temperature area from top to bottom in sequence; heating and melting the BaGa4Se7 polycrystal, and meanwhile, ensuring that at least part of the height of the BaGa4Se7 seed crystal in the vertical direction is not melted; cooling is conducted, the temperature of the melted materials is reduced, and crystal growth is conducted; and after the crystal growth is finished, reducing the temperature of the crystal growth furnace to room temperature, thereby obtaining the product. The selenium gallium barium single crystal which is large in size, few in crystal defect, good in integrity and uniform in structure can be prepared through the growth method.

Description

Technical Field

[0001] The present invention relates to the technical field of crystal growth. More specifically, it relates to a barium gallium selenide single crystal and a method for growing the same. Background Art

[0002] Barium gallium selenide (BaGa4Se7, hereinafter referred to as BGSe) crystal is a new type of wide-bandgap infrared nonlinear optical material with excellent comprehensive properties. It has a relatively high transmittance in the wavelength range of 0.47 - 18 μm, and there is only one absorption peak at about 15 μm. The second harmonic generation efficiency of BGSe crystal is 2 - 3 times that of AgGaS2 crystal, the damage threshold is about 3.7 times that of AgGaS2 crystal, and the maximum nonlinear coefficient is 24.3 pm / V. In addition, BGSe crystal also has a moderate birefringence and a high laser damage threshold, which makes it have great application potential in the fields of infrared laser modulation, optical communication, optical information processing, lidar, etc.

[0003] BGSe crystal shows broad application prospects in multiple fields. In the field of infrared lasers, BGSe crystal can convert the existing near-infrared laser (1 - 2 μm) to the mid- and far-infrared band (3 - 20 μm) through frequency down-conversion technologies such as optical parametric oscillation, generating tunable mid- and far-infrared lasers. This is of great significance in the fields of infrared remote sensing, laser communication, medical detection, and semiconductor processing. BGSe crystal performs excellently in high-power and wide-band infrared laser frequency conversion, and can achieve continuously tunable mid- and far-infrared laser output through OPO and OPA technologies.

[0004] The traditional vertical Bridgman method uses seed-induced growth, but barium gallium selenide crystal is prone to form micro-twins and dislocation defects in the high-temperature molten state; meanwhile, the uneven distribution of thermal stress at the solid-liquid interface easily leads to crystal cracking. In addition, the difference in thermal expansion coefficients between the seed crystal and the melt may cause interface mismatch, reducing the crystal integrity. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide a barium gallium selenide single crystal and a method for growing the same. Through this growth method, a large-sized (for example, the crystal is a cylinder with a cylinder diameter of more than 50 mm), barium gallium selenide single crystal with few crystal defects, good integrity, and uniform structure can be prepared.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] On the one hand, the present invention provides a method for growing a barium gallium selenide single crystal, the chemical formula of the barium gallium selenide single crystal is BaGa4Se7, belonging to the monoclinic system, the space group is Pc, and the unit cell parameters are: α = γ = 90°, β = 121.24(2)°;

[0008] The growth method includes the following steps:

[0009] Place the crucible containing BaGa4Se7 seed crystal and BaGa4Se7 polycrystal in a quartz tube, evacuate the quartz tube and fill it with argon, and then seal the quartz tube.

[0010] Place the quartz tube in a crystal growth furnace, where the crystal growth furnace is vertically arranged from top to bottom as a high-temperature zone, a gradient cooling zone, and a low-temperature zone in sequence.

[0011] Heat up and melt the BaGa4Se7 polycrystal, while ensuring that at least part of the height of the BaGa4Se7 seed crystal in the vertical direction is not melted.

[0012] Cool down, so that the temperature of the melted material decreases and crystal growth occurs.

[0013] After the crystal growth is completed, cool down the temperature of the crystal growth furnace to room temperature to obtain the barium gallium selenide single crystal.

[0014] Further, the BaGa4Se7 seed crystal is cylindrical, and the ratio of the cross-sectional diameter to the length is (4 - 8):(40 - 60).

[0015] Further, the ratio of the cross-sectional diameter to the length of the BaGa4Se7 seed crystal is 6:50.

[0016] Further, the preparation of the BaGa4Se7 polycrystal includes the following steps:

[0017] Mix elemental Ba, elemental Ga, and elemental Se in a molar ratio of 1:4:7, and then place them in a quartz tube.

[0018] Evacuate the quartz tube and then seal it, and then put it into a synthesis furnace.

[0019] Under an argon atmosphere, raise the internal furnace temperature of the synthesis furnace to 980 - 1000 °C and keep it warm for 30 - 50 h.

[0020] Then raise the temperature by 50 - 70 °C and keep it warm for 100 - 120 h, and during the heat preservation process, shake the quartz tube.

[0021] Cool down to room temperature at a rate of 10 - 20 °C / h to obtain the BaGa4Se7 polycrystal.

[0022] In the above preparation method, shaking the quartz tube can make the temperature of the substances in the tube more uniform and avoid the influence of local areas with too high or too low temperature on the preparation of the polycrystal.

[0023] Further, in the preparation of BaGa4Se7 polycrystal, the quartz tube is first soaked, cleaned, and dried with aqua regia before use.

[0024] Further, the vacuum degree in the quartz tube is 10 -4 ~10 -6 Pa, and the amount of argon gas filled is 0.3 - 1.0 atm (preferably 0.5 atm).

[0025] In the above technical solution, between the high - temperature zone and the gradient cooling zone, and between the gradient cooling zone and the low - temperature zone are connected, and the highest temperature of the gradient cooling zone is the same as the temperature of the high - temperature zone, and the lowest temperature of the gradient cooling zone is the same as the temperature of the low - temperature zone.

[0026] Further, in the quartz tube, a part of the crucible is located in the high - temperature zone, and another part is located in the gradient cooling zone, and in the crucible, the bottom end of the BaGa4Se7 seed crystal is located at the middle position of the gradient cooling zone;

[0027] The conditions for heating and melting the BaGa4Se7 polycrystal are as follows:

[0028] The high - temperature zone is heated to 1060 - 1070 °C at a heating rate of 80 - 100 °C / h, the low - temperature zone is heated to 950 - 970 °C, and the temperature of the gradient cooling zone is adjusted at a rate of 4 - 6 °C / cm (preferably 5 °C / cm) vertically from top to bottom;

[0029] After the above heating, keep the temperature constant for 60 - 80 hours.

[0030] In the above method for adjusting the temperature of the gradient cooling zone, it means that in the gradient cooling zone, the temperature in the vertical direction is decreased at a rate of 4 - 6 °C / cm vertically from top to bottom. By setting the temperature of the high - temperature zone, the temperature of the low - temperature zone, and the temperature - decreasing gradient of the gradient cooling zone, and then placing the bottom end of the seed crystal at the middle position of the gradient cooling zone, it is helpful to obtain a high - quality single crystal with large size, high quality, good uniformity and stability, and no obvious defects such as micro - twins and dislocations.

[0031] Further, the conditions for cooling and growing the crystal are: uniformly reducing the temperature of each temperature zone at a speed of 0.08 - 0.12 °C / h. Under the crystal - growing conditions of the present invention, each temperature zone reduces the crystal - growing temperature at a substantially same cooling speed, and by strictly controlling the rate of cooling and growing the crystal, the grown single crystal has the characteristics of large size, high quality, good uniformity and stability, and no obvious micro - twin and dislocation defects.

[0032] Even further, the conditions for cooling and growing the crystal are: uniformly reducing the temperature of each temperature zone at a speed of 0.1 °C / h.

[0033] In the present invention, "each temperature zone" refers to the high - temperature zone, the gradient cooling zone, and the low - temperature zone.

[0034] Further, after the crystal growth is completed, the method for reducing the temperature of the crystal growth furnace to room temperature is as follows:

[0035] Reduce the temperature of each temperature zone by 200 °C at a rate of 1-10 °C / h, and then reduce the temperature of each temperature zone to room temperature at a rate of 10-50 °C / h.

[0036] Further, a first thermocouple for real-time monitoring of the temperature of the crystal growth interface is provided in the crystal growth furnace, and the position of the first thermocouple is controlled to change with the change of the position of the crystal growth interface. The initial position of the monitoring point of the first thermocouple is flush with the growth interface at the start of growth. The position of the temperature-measuring first thermocouple changes with the change of the position of the crystal growth interface, and the temperature at the growth interface is fed back in real time, and the phase change process is tracked in real time. Uniform growth is achieved by adjusting the power of each heating module.

[0037] Further, in the crystal growth furnace, the quartz tube is fixed on a quartz support rod, and a second thermocouple for monitoring the temperature at the upper end of the BaGa4Se7 seed crystal and a third thermocouple for detecting the temperature at the lower end of the BaGa4Se7 seed crystal are provided on the quartz support rod. By monitoring the temperatures at the upper and lower ends of the BaGa4Se7 seed crystal with the temperature-measuring thermocouples, the temperatures at the upper and lower ends of the BaGa4Se7 seed crystal can be further adjusted and controlled accordingly to ensure that at least 2 / 5 of the length (preferably at least 20 mm in length) of the BaGa4Se7 seed crystal in the vertical direction is not melted.

[0038] Further, before the quartz tube is sealed by melting, the method further includes filling the remaining space in the quartz crucible with a hollow sealed quartz tube. During the process of loading the BaGa4Se7 seed crystal and BaGa4Se7 polycrystal into the crystal growth furnace, after placing the crucible in the quartz tube, evacuating the quartz tube and filling it with argon, filling the remaining space in the quartz crucible with a hollow sealed quartz tube, and finally sealing the quartz tube with a hydrogen-oxygen flame. The hollow sealed quartz tube filled in the quartz crucible can reduce the free volume and prevent decomposition and compositional deviation during the crystal growth process.

[0039] Further, during the growth process of the barium gallium selenide single crystal of the present invention, the position of the crucible relative to the crystal growth furnace remains relatively stationary. By controlling the growth conditions, precise temperature control is achieved to move the growth interface. There is no mechanical vibration during the whole growth process, which can effectively reduce crystal defects; at the same time, the intensity of thermal convection instability in the crystal melt is also reduced, and the uniformity of the crystal is improved.

[0040] On the other hand, the present invention provides a barium gallium selenide single crystal grown by the growth method described in the first aspect above.

[0041] The beneficial effects of the present invention are as follows:

[0042] The method for preparing by using the seed crystal vertical ultra-micro gradient condensation method adopted in the present invention avoids vibration during the crystal growth process, ensuring the uniformity and stability of the crystal. Keeping the position of the crucible relative to the crystal growth furnace relatively stationary and controlling the temperature gradient of the three temperature zones precisely for crystal growth can effectively reduce the incorporation of impurities and the introduction of various factors that may affect the crystal integrity; in addition, optimizing the temperature gradient can significantly reduce defects such as dislocations and micro-twins in the crystal, improving the crystal integrity, which not only avoids the common cracking and composition segregation problems in traditional methods, but also improves the overall quality of the crystal; in this method, by setting a high-temperature zone, a gradient cooling zone and a low-temperature zone, a more uniform temperature distribution is provided for crystal growth, ensuring the relative consistency of the crystal growth environment in different regions of the crystal, and improving the stability and reliability of the crystal. This method allows flexible adjustment of the crystal growth rate, realizes the optimization of the growth rate on the premise of ensuring the crystal quality, finds the best balance point between quality and speed, thereby improving production efficiency. Stable growth conditions avoid growth interruption or non-uniformity caused by temperature fluctuations, ensuring the continuity and stability of the crystal growth process, which is beneficial to the preparation of large-size and high-quality barium gallium selenide single crystals.

[0043] In addition, in this growth method, using BaGa4Se7 polycrystal as the crystal growth raw material improves the mechanical properties and stability of the material, further improving the overall properties of the material, including electrical and optical properties, providing strong support for the application of barium gallium selenide single crystals in the field of high-performance nonlinear optical crystals; filling the remaining space in the quartz crucible with a hollow sealed quartz tube reduces the free volume in the crystal growth space, and combined with filling with argon gas, it can effectively prevent decomposition and component deviation; finally, the entire crystal growth process monitors the temperature change at the crystallization isothermal surface in real time through a thermocouple, and adjusts the heating power of the controller to ensure the uniform growth of the crystal, avoiding crystal defects caused by excessive temperature difference, and realizing the growth of large-size barium gallium selenide single crystals. Through the slow and uniform cooling process of the three temperature zones simultaneously, the thermal stress caused by rapid cooling is reduced, making the distribution of residual stress inside the crystal more uniform, reducing the stress concentration inside the crystal, and improving the stability and reliability of the crystal. This effectively reduces the cracks generated during the crystal growth process, improves the yield rate, reduces the production cost, ensures the integrity and performance stability of the crystal during subsequent processing and application, and is of great significance for improving the product quality and market competitiveness. Brief Description of the Drawings

[0044] The following further elaborates in detail on the specific implementation manners of the present invention in conjunction with the drawings.

[0045] Figure 1 Shows a schematic diagram of an exemplary crystal growth device.

[0046] Figure 2Shows the appearance morphology diagram of the single crystal obtained in Example 2.

[0047] Figure 3 Shows the appearance morphology diagram of the single crystal obtained in Example 3.

[0048] Figure 4 Shows the comparison diagram of the crystal transmittance obtained in Example 2 and Example 3.

[0049] Figure 5 Shows the appearance morphology diagram of the single crystal obtained in Example 5.

[0050] Figure 6 Shows the appearance morphology diagram of the single crystal obtained in Example 6. Detailed implementation manners

[0051] To illustrate the present invention more clearly, the present invention will be further described below in conjunction with preferred embodiments and the accompanying drawings. Similar components in the drawings are denoted by the same reference numerals. Those skilled in the art should understand that the content specifically described below is illustrative rather than restrictive, and should not be used to limit the protection scope of the present invention.

[0052] Example 1

[0053] Synthesis of barium gallium selenium polycrystal (BaGa4Se7 polycrystal):

[0054] Material preparation: High-purity elemental Ba, Ga, and Se are weighed according to a molar ratio of 1:4:7; the quartz tube is soaked, cleaned, and dried with aqua regia.

[0055] Synthesis steps:

[0056] 1) After mixing the weighed Ba, Ga, and Se evenly, load them into the pre-treated quartz tube; evacuate the quartz tube containing the raw materials to 10 -4 Pa, and then seal it with a hydrogen-oxygen flame to form a sealed reaction vessel;

[0057] 2) Place the sealed quartz tube into a horizontal high-temperature and high-pressure synthesis furnace, fill the furnace chamber with 10 atm of argon to establish a protective atmosphere; heat up to 980 °C and keep it at a constant temperature for 30 hours to complete the preliminary reaction; continue to heat up to 1030 °C, and periodically shake the quartz tube through a mechanical lifting device for 100 hours to promote the formation of polycrystals;

[0058] 3) Slowly cool down to room temperature at a rate of 10 °C / h to obtain a high-purity barium gallium selenium polycrystal raw material.

[0059] Results:

[0060] Through the above steps, high-purity polycrystalline raw materials of barium gallium selenide were successfully synthesized, providing a high-quality raw material basis for subsequent single-crystal growth. The synthesized polycrystalline raw materials have good crystallinity and purity, meeting the requirements of single-crystal growth.

[0061] Example 2

[0062] Growth of barium gallium selenide single crystal (BaGa4Se7 single crystal):

[0063] Material preparation: High-purity polycrystalline raw materials of barium gallium selenide prepared in Example 1; cylindrical BaGa4Se7 seed crystal, a cylindrical crystal with a cross-sectional diameter of 6 mm and a length of 50 mm; cylindrical crucible made of PBN, with a seed crystal groove of Φ6 mm×50 mm designed at the bottom; quartz tube, which has been soaked, cleaned, and dried with aqua regia.

[0064] An exemplary crystal growth apparatus is as Figure 1 shown. The specific growth steps are as follows:

[0065] 1) Place the BaGa4Se7 seed crystal into the seed crystal groove at one end of the PBN crucible, and then add about 1100 g of high-purity polycrystalline raw materials of barium gallium selenide; place the PBN crucible containing the seed crystal and polycrystalline raw materials vertically in the quartz tube, and the diameter of the quartz tube is Φ50 mm; evacuate the quartz tube to 10 -4 Pa and then fill it with 0.5 atm of argon, and use a hollow-sealed quartz tube to fill the remaining space in the quartz crucible. Finally, seal the quartz tube with a hydrogen-oxygen flame;

[0066] 2) Place the sealed quartz tube on a special quartz support rod and put it into a vertical three-temperature-zone gradient condensation growth furnace. The growth furnace is successively a high-temperature zone (1060 °C), a gradient cooling zone (gradient of 5 °C / cm), and a low-temperature zone (950 °C) from top to bottom;

[0067] 3) Raise the temperature of the high-temperature zone to 1060 °C and the low-temperature zone to 950 °C at a heating rate of 80 °C / h, and adjust the temperature of the gradient cooling zone at a gradient of 5 °C / cm to ensure that more than 20 mm of the seed crystal is not melted, and keep it at a constant temperature for 60 hours; keep the quartz tube and the growth furnace stationary, and cool it uniformly at a speed of 0.1 °C / h to slowly lower the temperature of the melted material and crystallize for crystal growth. Monitor the temperature at the growth interface in real time through the thermocouple, and achieve uniform growth by adjusting the power of each heating module;

[0068] 4) After the growth is completed, reduce the temperature of each temperature zone of the growth furnace by 200 °C at a speed of 1 °C / h, and then reduce it to room temperature at a speed of 10 °C / h; take out the grown BaGa4Se7 single crystal from the crucible.

[0069] Results:

[0070] Through the above steps, large-sized and high-quality barium gallium selenide single crystals were successfully grown. The grown single crystals have good uniformity and stability, without obvious micro-twins and dislocation defects, meeting the application requirements of high-performance nonlinear optical crystals. The appearance morphology diagram of the single crystal is as shown in Figure 2 shown. The single crystal is cylindrical, with a diameter of 50 mm and a length of 114 mm.

[0071] Example 3

[0072] Growth of barium gallium selenide single crystal:

[0073] Material preparation: High-purity barium gallium selenide polycrystalline raw materials; BaGa4Se7 seed crystal, a cylindrical crystal with a cross-sectional diameter of 6 mm and a length of 50 mm; a cylindrical crucible made of PBN, with a seed crystal groove of Φ6 mm × 50 mm designed at the bottom; a quartz tube, which has been soaked, cleaned, and dried in aqua regia.

[0074] Growth steps:

[0075] 1) Place the BaGa4Se7 seed crystal into the seed crystal groove at one end of the PBN crucible, and then add about 2700 g of high-purity barium gallium selenide polycrystalline raw materials; place the PBN crucible containing the seed crystal and polycrystalline raw materials vertically in a quartz tube with a diameter of Φ80 mm. Vacuum the quartz tube to 10 -4 Pa and then fill it with 0.5 atm of argon gas. Seal the remaining space in the quartz crucible with a hollow-sealed quartz tube. Finally, seal the quartz tube with a hydrogen-oxygen flame;

[0076] 2) Place the sealed quartz tube on a special quartz support rod and put it into a vertical three-temperature-zone gradient condensation growth furnace. The growth furnace consists of a high-temperature zone (1060 °C), a gradient cooling zone (with a gradient of 5 °C / cm), and a low-temperature zone (950 °C) from top to bottom;

[0077] 3) Raise the temperature of the high-temperature zone to 1060 °C and the low-temperature zone to 950 °C at a heating rate of 80 °C / h. Adjust the temperature of the gradient cooling zone at a gradient of 5 °C / cm to ensure that more than 20 mm of the seed crystal is not melted. Keep the temperature constant for 60 hours; Keep the quartz tube and the growth furnace stationary and cool down uniformly at a rate of 0.1 °C / h to slowly lower the temperature of the melted material and crystallize it for crystal growth;

[0078] 4) After the growth is completed, lower the temperature of each temperature zone of the growth furnace by 200 °C at a rate of 1 °C / h, and then lower it to room temperature at a rate of 10 °C / h; Take out the grown BaGa4Se7 single crystal from the crucible.

[0079] Results:

[0080] Through the above steps, the grown barium gallium selenide single crystals have obvious micro-twins and dislocation defects and cannot meet the application requirements of high-performance nonlinear optical crystals. The appearance morphology diagram of the single crystal is as shown inFigure 3 As shown. The single crystal is cylindrical, with a diameter of 80 mm and a length of 102 mm.

[0081] The transmittance comparison chart of the single crystals prepared in the above Example 2 and Example 3 is as Figure 4 shown. It can be seen that the transmittance of the single crystal obtained in Example 2 is better than that in Example 3.

[0082] Example 4

[0083] Growth of barium gallium selenium single crystal:

[0084] Material preparation:

[0085] Material preparation: High-purity barium gallium selenium polycrystalline raw material; BaGa4Se7 seed crystal, a cylindrical crystal with a cross-sectional diameter of 6 mm and a length of 50 mm; a cylindrical crucible made of PBN, with a seed crystal groove of Φ6 mm×50 mm designed at the bottom; a quartz tube, which has been soaked, cleaned and dried with aqua regia.

[0086] Growth steps:

[0087] 1) Place the BaGa4Se7 seed crystal into the seed crystal groove at one end of the PBN crucible, and then put in the high-purity barium gallium selenium polycrystalline raw material; place the PBN crucible containing the seed crystal and polycrystalline raw material vertically in the quartz tube, and evacuate the quartz tube to 10 -4 Pa;

[0088] 2) Place the sealed quartz tube on a special quartz support rod and put it into a vertical three-temperature zone gradient condensation growth furnace. The growth furnace is successively a high-temperature zone (1060 °C), a gradient cooling zone (5 °C / cm gradient) and a low-temperature zone (970 °C) from top to bottom;

[0089] 3) Raise the high-temperature zone to 1060 °C at a heating rate of 80 °C / h, raise the low-temperature zone to 970 °C, and adjust the temperature of the gradient cooling zone at a gradient of 5 °C / cm to ensure that more than 20 mm of the seed crystal is not melted, and keep the temperature constant for 60 hours; keep the quartz tube and the growth furnace stationary, and cool down uniformly at a speed of 0.1 °C / h to slowly lower the temperature of the melted material and crystallize for crystal growth. Monitor the temperature at the growth interface in real time through the thermocouple, and achieve uniform growth by adjusting the power of each heating module;

[0090] 4) After the growth is completed, each temperature zone of the growth furnace is lowered by 300 °C at a speed of 1 °C / h, and then lowered to room temperature at a speed of 10 °C / h.

[0091] Result:

[0092] Since no argon gas was filled in the quartz tube, the quartz tube collapsed during the growth process, and the BaGa4Se7 single crystal was not grown.

[0093] Example 5

[0094] Growth of Selenium-Gallium-Barium Single Crystal

[0095] Material Preparation

[0096] Material Preparation: High-purity polycrystalline selenium-gallium-barium raw materials; BaGa4Se7 seed crystals, cylindrical crystals with a cross-sectional diameter of 6 mm and a length of 50 mm; cylindrical crucibles made of PBN with a seed crystal groove of Φ6 mm×50 mm designed at the bottom; quartz tubes, which have been soaked, cleaned, and dried with aqua regia.

[0097] Growth Steps

[0098] 1) Place the BaGa4Se7 seed crystal into the seed crystal groove at one end of the PBN crucible, and then put about 1000 g of high-purity polycrystalline selenium-gallium-barium raw materials; place the PBN crucible containing the seed crystal and polycrystalline raw materials vertically in a quartz tube with a diameter of Φ40 mm, evacuate the quartz tube to 10 -4 Pa and then fill it with 0.5 atm of argon gas, and use a hollow sealed quartz tube to fill the remaining space in the quartz crucible;

[0099] 2) Place the sealed quartz tube on a special quartz support rod and put it into a vertical three-temperature-zone gradient condensation growth furnace. The growth furnace consists of a high-temperature zone (1060 °C), a gradient cooling zone (with a gradient of 4 °C / cm), and a low-temperature zone (950 °C) from top to bottom;

[0100] 3) Raise the temperature of the high-temperature zone to 1060 °C at a heating rate of 80 °C / h, raise the temperature of the low-temperature zone to 950 °C, and adjust the temperature of the gradient cooling zone at a gradient of 4 °C / cm to ensure that more than 20 mm of the seed crystal is not melted, and keep it at a constant temperature for 60 hours; keep the quartz tube and the growth furnace stationary, and cool it uniformly at a rate of 0.1 °C / h to slowly lower the temperature of the melted material and crystallize it for crystal growth;

[0101] 4) After the growth is completed, lower the temperature of each temperature zone of the growth furnace by 200 °C at a rate of 1 °C / h, and then lower it to room temperature at a rate of 10 °C / h; take out the grown BaGa4Se7 single crystal from the crucible.

[0102] Results

[0103] By adjusting the temperature gradient of the gradient cooling zone to 4 °C / cm, high-quality selenium-gallium-barium single crystals were successfully grown. The grown single crystals have good uniformity and stability, without obvious micro-twinning and dislocation defects, meeting the application requirements of high-performance nonlinear optical crystals. The appearance morphology diagram of the single crystal is as Figure 5 shown. The single crystal is cylindrical, with a diameter of 40 mm and a length of 141 mm.

[0104] Example 6

[0105] Growth of Selenium-Gallium-Barium Single Crystal

[0106] Material preparation: High-purity selenium-gallium-barium polycrystalline raw materials; BaGa4Se7 seed crystal, a cylindrical crystal with a cross-sectional diameter of 6 mm and a length of 50 mm; a cylindrical crucible made of PBN, with a seed crystal groove of Φ6 mm × 50 mm designed at the bottom; a quartz tube, which has been soaked, cleaned, and dried with aqua regia.

[0107] Growth steps:

[0108] 1) Place the BaGa4Se7 seed crystal into the seed crystal groove at one end of the PBN crucible, and then add about 1800 g of high-purity selenium-gallium-barium polycrystalline raw materials; place the PBN crucible containing the seed crystal and polycrystalline raw materials vertically in a quartz tube with a diameter of Φ50 mm, evacuate the quartz tube to 10 -4 Pa and then fill it with 0.5 atm of argon gas, and use a hollow-sealed quartz tube to fill the remaining space in the quartz crucible;

[0109] 2) Place the sealed quartz tube on a special quartz support rod and put it into a vertical three-temperature-zone gradient condensation growth furnace. The growth furnace from top to bottom is a high-temperature zone (1060 °C), a gradient cooling zone (5 °C / cm gradient), and a low-temperature zone (950 °C);

[0110] 3) Raise the high-temperature zone to 1060 °C at a heating rate of 80 °C / h, raise the low-temperature zone to 950 °C, and adjust the temperature of the gradient cooling zone at a gradient of 5 °C / cm to ensure that more than 20 mm of the seed crystal is not melted, and keep it at a constant temperature for 60 hours; keep the quartz tube and the growth furnace stationary, and cool it uniformly at a rate of 0.5 °C / h to slowly lower the temperature of the melted material and crystallize it for crystal growth. Monitor the temperature at the growth interface in real time through a thermocouple, and achieve uniform growth by adjusting the power of each heating module;

[0111] 4) After the growth is completed, cool each temperature zone of the growth furnace to 850 °C at a rate of 1 °C / h, and then cool it to room temperature at a rate of 10 °C / h; take out the grown BaGa4Se7 single crystal from the crucible.

[0112] Results:

[0113] By adjusting the cooling rate to 0.5 °C / h, the grown selenium-gallium-barium single crystal has obvious micro-twinning and dislocation defects, and cannot meet the application requirements of high-performance nonlinear optical crystals. The appearance morphology diagram of this single crystal is as Figure 6 shown. This single crystal is cylindrical, with a diameter of 50 mm and a length of 162 mm.

[0114] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A method for growing a selenium-gallium-barium single crystal, characterized in that, The chemical formula of the barium gallium selenide single crystal is BaGa4Se7, belonging to the monoclinic crystal system, with the space group Pc and the unit cell parameters as follows: α = γ = 90°, β = 121.24(2)°; The growth method includes the following steps: Place the crucible containing the BaGa4Se7 seed crystal and BaGa4Se7 polycrystal in a quartz tube, evacuate the quartz tube and fill it with argon, and then seal the quartz tube. Place the quartz tube in a crystal growth furnace, where the crystal growth furnace is vertically arranged from top to bottom as a high-temperature zone, a gradient cooling zone, and a low-temperature zone in sequence. Heat up and melt the BaGa4Se7 polycrystal, while ensuring that at least part of the height of the BaGa4Se7 seed crystal in the vertical direction is not melted. Cool down so that the temperature of the melted material decreases and crystal growth occurs. After the crystal growth is completed, cool the temperature of the crystal growth furnace to room temperature to obtain the barium gallium selenide single crystal.

2. The growth method according to claim 1, characterized in that, The BaGa4Se7 seed crystal is cylindrical, and the ratio of the cross-sectional diameter to the length is (4 - 8):(40 - 60).

3. The growth method according to claim 1, wherein The preparation of the BaGa4Se7 polycrystal includes the following steps: Mix elemental Ba, elemental Ga, and elemental Se in a molar ratio of 1:4:7, and place them in a quartz tube. Evacuate and seal the quartz tube, and then put it into a synthesis furnace. Under an argon atmosphere, raise the internal furnace temperature of the synthesis furnace to 980 - 1000 °C and keep it warm for 30 - 50 h. Then raise the temperature by 50 - 70 °C and keep it warm for 100 - 120 h. During the heat preservation process, shake the quartz tube. Cool it down to room temperature at a rate of 10 - 20 °C / h to obtain the BaGa4Se7 polycrystal.

4. The growth method according to claim 1, wherein, The vacuum degree in the quartz tube is 10 -4 ~10 -6 Pa, and the amount of argon filled is 0.3 - 1.0 atm.

5. The growth method according to claim 1, characterized in that, In the quartz tube, a part of the crucible is located in the high-temperature zone, and the other part is located in the gradient cooling zone. In the crucible, the bottom end of the BaGa4Se7 seed crystal is located at the middle position of the gradient cooling zone. The conditions for heating up and melting the BaGa4Se7 polycrystal are as follows: Raise the temperature of the high-temperature zone to 1060 - 1070 °C and the low-temperature zone to 950 - 970 °C at a heating rate of 80 - 100 °C / h, and adjust the temperature of the gradient cooling zone at a rate of 4 - 6 °C / cm vertically from top to bottom. After the above heating, keep the temperature constant for 60 - 80 hours.

6. The growth method according to claim 1, characterized in that, The conditions for cooling and growing crystals are: uniformly reduce the temperature of each temperature zone at a rate of 0.08 - 0.12 °C / h.

7. The growth method according to claim 1, wherein After the crystal growth is completed, the method for cooling the temperature of the crystal growth furnace to room temperature is: Reduce the temperature of each temperature zone by 200 - 300 °C at a rate of 1 - 10 °C / h respectively, and then reduce the temperature of each temperature zone to room temperature at a rate of 10 - 50 °C / h.

8. According to the growth method described in claim 1, characterized in that A first thermocouple for monitoring the temperature of the crystal growth interface is provided in the crystal growth furnace, and the position of the first thermocouple is controlled to change with the position of the crystal growth interface. In the crystal growth furnace, the quartz tube is fixed on a quartz support rod, and a second thermocouple for monitoring the temperature of the upper end of the BaGa4Se7 seed crystal and a third thermocouple for detecting the temperature of the lower end of the BaGa4Se7 seed crystal are provided on the quartz support rod.

9. The growth method according to claim 1, wherein Before sealing the quartz tube, the method further includes filling the remaining space in the quartz crucible with a hollow sealed quartz tube.

10. A barium gallium selenide single crystal grown by the growth method according to any one of claims 1 - 9.

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