Method for vertically and directionally growing KTF crystal

Abstract

The invention relates to a method for vertically and directionally growing a KTF crystal, which comprises the following steps of: a, directionally cutting and rounding a KTF single crystal along the direction of the crystal (111) to obtain a cylindrical single crystal rod which is axially parallel to the direction of the crystal (111) and is used as a seed crystal required by directional growth; b, respectively carrying out fluorination treatment on two raw materials of KF and TbF3 with the purity of more than or equal to 99.99% at different high temperatures, and storing the treated raw materials in a drying oven at the temperature of 100 DEG C for later use; c, carrying out heat treatment and cleaning on a graphite crucible, putting the prepared seed crystal into a seed crystal hole in the bottom of the crucible, adding a gasket, and covering a bottom cover; d, covering a furnace cover, starting a mechanical pump and a diffusion pump to enable vacuum to reach 5 * 10 <-4 > Pa, and filling Ar gas and CF4 mixed gas to a 0 position of a barometer; e, starting a power supply for heating, wherein the set ratio of the upper power W1 to the lower power W2 is W1: W2 = 2: 1; f, in a positive pressure state, growing the KTF crystal at a descending speed of 0.5-3mm / h to obtain the KTF crystal in a (111) direction; and g, annealing to normal temperature at a certain cooling speed after crystal growth is finished.

Description

Technical Field

[0001] The patent of this invention relates to a method for vertically oriented growth of KTF crystals, belonging to the field of artificial crystal technology. Background Art

[0002] Magneto-optical isolators are core components of high-power / high-energy laser systems. They can ensure unidirectional transmission of lasers and prevent strong emission light from damaging the front-end seed source or cavity mirror. Currently, the single-channel power of isolators made of commercial TGG crystals does not exceed 200W, which is difficult to meet the application requirements of many special occasions, such as high-energy space-based lidar, nuclear fusion confinement, and laser weapon systems. In response to the needs of high-power / high-energy laser systems, the American company SYNOPCS developed high-performance KTF / LTF crystals in 2017. The tested single-channel power exceeded 400W, and it is predicted that it will eventually exceed 1000W and will be commercialized later. Many domestic research institutions conducted research and development of KTF crystals around 2019, but no progress was made. Summary of the invention

[0003] In order to solve the technical difficulties in KTF crystal growth, the patent of this invention provides a new technology that can automatically grow KTF crystals. It can not only grow crystals with a diameter of 10-80mm and a crystal orientation of (111), but also the internal quality of the crystals can meet the requirements of commercial high-power isolators.

[0004] The technical solution adopted by the present invention to solve the technical problem is:

[0005] A method for vertically oriented growth of a KTF crystal, the crystal growth process sequentially comprising the following steps:

[0006] a) Preparation of seed crystal: KTF single crystal is cut along the (111) direction of the crystal and rolled into a round shape to obtain a cylindrical single crystal rod with the axis parallel to the (111) direction of the crystal, which is used as the seed crystal required for directional growth.

[0007] b) Pretreatment of raw materials: Add KF powder into a reagent bottle, pour in hydrofluoric acid solution, prepare KFHF colloid, put it into a graphite crucible, put it into the raw material sintering furnace, and evacuate to 5*10 -4 Pa, fill with Ar gas and CF4 mixed gas, keep constant temperature at 200℃-300℃ for 12 hours, take it out and put it in a 100℃ drying oven for future use; put TbF3 raw material into graphite crucible, evacuate to 5*10 -4 Below Pa, fill with Ar gas and CF4 mixed gas, deoxidize and melt the raw materials at a high temperature of 1200℃-1300℃ for 8-12 hours. After taking out, grind the broken crystals into small pieces with a diameter of 1-3mm and put them into a 100℃ drying oven for storage.

[0008] c) Crucible treatment and loading: Heat treat the graphite crucible, clean it, put the prepared seed crystal into the seed crystal hole at the bottom of the crucible, add a gasket and cover the bottom cover. Put the crucible upright, add the processed KFHF and TbF3 raw materials according to the molar ratio of KF and TbF3 of 27%:73%, put it into the dual-temperature zone vertical directional crystallization furnace, and cover the crucible.

[0009] d) Place the temperature field, cover the furnace, turn on the mechanical pump and diffusion pump, and draw the vacuum degree in the furnace to 5*10 -4 Then fill in Ar gas and CF4 gas in the ratio of 10:1 to the 0 position of the pressure gauge.

[0010] e) Heating and melting: Turn on the power to increase the temperature. The ratio of upper power W1 to lower power W2 is W1:W2=2:1. The temperature reaches the overheating range of 1120℃-1180℃ above the melting point 1050℃. The temperature needs to be kept constant for 2-3 hours to make the melt temperature evenly distributed.

[0011] f) Crystallization: Under positive pressure, KTF crystals are grown at a descent rate of 0.5-3 mm / h to obtain KTF crystals in the (111) direction.

[0012] g) Annealing: After the crystal growth is completed, anneal to room temperature at a certain cooling rate.

[0013] Preferably, the diameter of the seed crystal in the (111) direction is 2-6 mm; the diameter of the seed crystal hole is 3-10 mm and the length is 20-30 mm; preferably; 0≤the diameter of the seed crystal hole-the diameter of the seed crystal≥1 mm.

[0014] Preferably, before placing the seed crystal in the (111) direction into the seed crystal hole, the seed crystal is ultrasonically cleaned using acetone, ethanol and deionized water as cleaning agents in sequence, each cleaning lasting 20 minutes. The seed crystal is dried in a drying oven at 150° C. for 2 hours before use.

[0015] Preferably, the purity of the KF and TbF3 starting reagent powders is ≥99.99%, and the purity of the Ar gas and CF4 gas is ≥99.999%.

[0016] Preferably, since KF will lose part of its volatilization at high temperature, according to KTF (KTb3O 10 ) The chemical equation and the results of multiple experiments show that KTF crystals with better internal quality can be obtained by growing crystals according to the molar ratio of KF to TbF3 of 27%:73%.

[0017] Preferably, crystals are grown in a mixed gas atmosphere of Ar gas and CF4 gas. A high CF4 gas content is prone to corrode furnace vacuum components, while a low content cannot achieve the effect of deoxygenating the raw materials. A mixing ratio of Ar gas and CF4 gas of 10:1 is optimal.

[0018] Preferably, the crucible retention position is confirmed by testing TbF3 (melting point is 1160° C.) melted at different heights to find out the height at which the bottom of the crucible is suitable for retention. It is best if the melting area of ​​the seed crystal at this position reaches about 1 / 2 of the seed crystal.

[0019] Preferably, after testing experiments on different comparisons of the dual-zone powers, the dual-zone power is preferably W1:W2=2:1, which can achieve the temperature gradient required for KTF growth: 30°C-50°C / cm.

[0020] Preferably, the melting point of KTF crystal is 1050°C, and the temperature of crystal growth is preferably in the range of 1120°C-1180°C.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: the process of the present invention includes: preparation of seed crystals, pretreatment of raw materials, processing and loading of crucibles, vacuum and gas filling, heating and melting, crystallization, annealing, etc. The pretreatment of raw materials allows the two raw materials KF and TbF3 to meet the conditions required for crystal growth, and the upper and lower resistance heaters are used to control the power W1 / W2 ratio to achieve the temperature gradient required for KTF growth, thereby realizing the automation of the crystal growth process; the pretreatment of raw materials uses hydrofluoric acid and CF4 gas to fluorinate the raw materials to achieve the effect of deoxygenating the raw materials, which can meet the requirements of crystal growth.

[0022] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0024] Figure 1 It is the material weighing weight record table of the present invention;

[0025] Figure 2 This is a picture of the seven-hole crucible and seed crystal hole of the present invention;

[0026] Figure 3 This is a photo of the KTF crystal of the present invention;

[0027] Figure 4is the absorption diagram of the KTF crystal of the present invention;

[0028] Specific implementation methods:

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] See also Figure 1-4 The present invention provides a method and technical solution for vertical directional growth of KTF crystals: (1) a KTF single crystal block is directional cut along the crystal (111) direction, and rounded to obtain a KTF single crystal block parallel to the crystal (111) in the axial direction.

[0031] The cylindrical single crystal rod with a direction is used as the seed crystal required for directional growth. The processed seed crystal (diameter 3mm, length 20mm) is ultrasonically cleaned, and acetone, ethanol and deionized water are used as cleaning agents for ultrasonic cleaning for 20 minutes in turn to remove impurities such as oil and dirt adhered to the crystal block during the processing process; the seed crystal should be dried in a drying oven at 150℃ for 2 hours before use.

[0032] (2) Weigh 250 g of 99.99% KF powder and add it to a reagent bottle. Pour 200 ml of hydrofluoric acid solution to prepare KFHF colloid. Put KFHF into a graphite crucible and place it in a raw material sintering furnace. Vacuum to 5*10 -4 Pa, filled with Ar gas and CF4 mixed gas, kept constant temperature at 200℃-300℃ for 12 hours, took it out and put it in

[0033] Store in a 100℃ drying oven for later use; weigh 500g of 99.99% TbF3 raw material and put it into a graphite crucible, evacuate to

[0034] 5*10 -4 Pa, fill the mixed gas of Ar gas and CF4 gas in a ratio of 10:1 to the 0 position of the barometer.

[0035] Deoxidize and melt the raw materials at a high temperature of 1200℃-1300℃ for 8-12 hours. Grind the broken crystals into small pieces with a diameter of 1-3mm and store them in a drying oven at 100℃ for later use.

[0036] (3) Crucible treatment and loading: Place the seven-hole graphite crucible into the sintering furnace and set it at a vacuum of 5*10 -4Burn in the air at about 1400℃ below Pa, clean with a dust-free cloth, put the prepared seed crystal into the seed crystal hole at the bottom of the crucible, add a gasket and cover the bottom cover. Put the crucible upright, add the processed KFHF and TbF3 mixture according to the molar ratio of KF and TbF3 27%:73%, put it into the double temperature zone crucible descending method crystal growth furnace, and cover the crucible cover;

[0037] (4) Place the temperature field, cover the furnace, turn on the mechanical pump and diffusion pump, and draw the vacuum degree in the furnace to 5*10 -4 Below Pa, then fill in Ar gas and CF4 gas in a ratio of 10:1 to the 0 position of the barometer;

[0038] (5) Heating and melting: Turn on the power to increase the temperature, the upper power W1 reaches 6kw and the lower power W2 reaches 3kw, the temperature reaches about 1150℃, and keep the temperature constant for 3 hours;

[0039] (6) Crystallization: Under a positive pressure of 40 kPa, KTF crystals were grown at a descent rate of 2.5 mm / h for 35 hours to obtain KTF crystals in the (111) direction;

[0040] (7) Annealing: After the crystal growth is completed, anneal to room temperature at a certain cooling rate.

Claims

1. A method for vertically oriented growth of KTF crystals, characterized in that: The steps include: a) Preparation of seed crystal: KTF single crystal block is cut along the crystal (111) direction and rounded to obtain a cylindrical single crystal rod with the axis parallel to the crystal (111) direction, which is used as the seed crystal required for directional growth; b) Raw material pretreatment: The two raw materials KF and TbF3 with a purity of ≥99.99% are subjected to fluorination treatment at different high temperatures, and the treated raw materials are placed in a drying oven at 100°C for future use; c) Crucible treatment and loading: heat treat the graphite crucible, clean it, put the prepared seed crystal into the seed crystal hole at the bottom of the crucible, add a gasket and cover the bottom cover; put the crucible upright, weigh the processed KF and TbF3 raw materials according to the proportion, load them into the dual-temperature zone vertical directional crystallization furnace, and cover the crucible cover; d) Place the temperature field, close the furnace cover, turn on the mechanical pump and diffusion pump to make the vacuum reach 5*10 -4 Below Pa, fill with Ar gas and CF4 mixed gas to the barometer position 0; e) Heating and melting: Turn on the power to increase the temperature. The ratio of upper power W1 to lower power W2 is W1:W2=2:

1. The temperature reaches the range of 1120℃-1180℃. It takes 2-3 hours to keep the temperature constant so that the melt temperature is evenly distributed. f) Crystallization: Under positive pressure, KTF crystals are grown at a descending speed of 0.5-3 mm / h to obtain KTF crystals in the (111) direction; g) Annealing: After the crystal growth is completed, anneal to room temperature at a certain cooling rate.

2. A method for vertically oriented growth of KTF crystal according to claim 1, characterized in that: The diameter of the seed crystal in the (111) direction is 2-6 mm; the diameter of the seed crystal hole is 3-10 mm and the length is 20-30 mm; preferably; 0≤the diameter of the seed crystal hole-the diameter of the seed crystal in the (111) direction≥1 mm.

3. A method for vertically oriented growth of KTF crystal according to claim 2, characterized in that: Before placing the seed crystal in the (111) direction into the seed crystal hole, the seed crystal is ultrasonically cleaned using acetone, ethanol and deionized water as cleaning agents in sequence, each cleaning lasting 20 minutes, and in particular, it is dried in a drying oven at 150° C. for 2 hours before use.

4. A method for vertically oriented growth of KTF crystal according to claim 3, characterized in that: The purity of the KF and TbF3 powders is ≥99.99%; the fluoride deoxidizer is CF4 gas, the purity of which is ≥99.999%, the purity of Ar gas is ≥99.999%, and the ratio of the mixed gas Ar and CF4 gas is 10:

1.

5. A method for vertically oriented growth of KTF crystal according to claim 4, characterized in that: The high temperature fluorination treatment comprises: adding KF powder into a reagent bottle, pouring a hydrofluoric acid solution into it, preparing a KFHF colloid, loading it into a graphite crucible, placing it in a raw material sintering furnace, and evacuating it to 5*10 -4 Pa, fill with Ar gas and CF4 mixed gas, keep constant temperature at 200℃-300℃ for 12 hours, take it out and put it in a 100℃ drying oven for future use; put TbF3 raw material into graphite crucible, evacuate to 5*10 -4 Below Pa, fill with Ar gas and CF4 mixed gas, deoxidize and melt the raw materials at a high temperature of 1200℃-1300℃ for 8-12 hours. After taking out, grind the broken crystals into small pieces with a diameter of 1-3mm and put them into a 100℃ drying oven for storage.

6. A method for vertically oriented growth of KTF crystal according to claim 5, characterized in that: The graphite crucible used is a porous crucible, and a seed crystal hole is provided at the bottom of each hole, and the heater used is a double graphite resistance heater.

7. A method for vertically oriented growth of KTF crystal according to claim 6, characterized in that: Since KF will lose some of its content when volatilized at high temperature, according to KTF (KTb3O 10 ) The chemical equation and the results of multiple experiments show that the ratio of KF and TbF3 is 27% and 73%. According to this molar ratio, a certain weight of KFHF and TbF3 are weighed and mixed evenly.

8. A method for vertically oriented growth of KTF crystal according to claim 7, characterized in that: The growth of the KTF crystal includes: The vacuum degree in the crystallization furnace is reduced to 5*10 -4 Pa, and then fill with Ar gas and CF4 gas in a ratio of 10:1, raise the temperature of the graphite crucible in the furnace to 1120℃-1180℃ as the growth temperature, and keep it at the growth temperature for 2-3 hours to make the raw materials in the crucible fully melt and the temperature distribution uniform; Among them, in order to ensure the success of seed crystal inoculation, first determine the appropriate initial position of the crucible, the standard of the initial position of the crucible is to make the seed crystal just melt about 1 / 2 of its length at the set growth temperature; then grow the crystal at a descending speed of 0.5-3mm / h; after the growth is completed, cool to room temperature at a speed of 10-50℃ / hour.

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