A method for growing large-sized titanium-doped sapphire crystals by Kyropoulos method

Abstract

The present invention belongs to the technical field of crystal growth, and particularly relates to a method for growing large-size titanium-doped sapphire crystals by the Kyropoulos method. The method includes steps of raw material preparation and loading, heating up to melt the material, temperature adjustment and seeding, crystal growth, in-situ annealing during crystal cooling, and wafer H2 annealing. The present invention uses high-purity graphite materials to construct the thermal field, reducing thermal field pollution, precisely controlling the temperature distribution through a double heating body, and forming a stable temperature gradient field; during heating, a mixed gas of Ar and CO is introduced as a protective gas to inhibit adverse reactions in the furnace and maintain the stable existence of Ti 3+ ions in the melt; during the crystal growth process by the Kyropoulos method, it does not contact the crucible, reducing stress concentration, improving crystal uniformity, and realizing an efficient growth method for large-size, high-quality, and low-defect titanium-doped sapphire crystals, meeting the manufacturing requirements of high-end lasers and optical devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of crystal growth, and particularly relates to a method for growing large-size titanium-doped sapphire crystals by the Kyropoulos method. Background Art

[0002] Titanium-doped sapphire crystals (Ti:sapphire crystals) are mainly applied in the field of laser technology and are the most widely used tunable laser solid materials with excellent laser properties, such as wide emission bandwidth, excellent thermal, optical, physical, chemical, and mechanical properties. With the rapid development of the laser industry, the demand for all-solid-state lasers is continuously increasing. All-solid-state lasers made of titanium-doped sapphire have the characteristics of simple structure, convenient use, high power, wide tuning range, high working efficiency, high reliability, and long service life, and are widely used in the fields of laser spectroscopy, nonlinear optics, lithography technology, atmospheric monitoring, laser medicine, and scientific research. At present, there are mainly three technical difficulties in manufacturing large-size titanium-doped sapphire crystals internationally: ① It is difficult to grow large-diameter crystals (diameter greater than 200 mm); ② It is difficult to control the growth of crystals with high doping concentration and low defects; ③ It is difficult to control the uniform distribution of Ti 3+ concentration within a large diameter range.

[0003] The main methods for growing large-size titanium-doped sapphire crystals include the Czochralski method, the heat exchange method, the edge-defined film-fed growth method, the temperature gradient method, the Kyropoulos method, etc. The advantage of using the Kyropoulos method to grow large-size titanium-doped sapphire is that it can achieve precise control of the heat preservation thermal field, crystal growth atmosphere, growth gradient, etc., and produce large-diameter (>200 mm) crystals. However, since the ionic radius of the doped Ti 3+ is 0.076 nm, which is 43% larger than the ionic radius of Al 3+ in the alumina matrix (0.053 nm), during the process of growing large-size titanium-doped sapphire crystals, there is a strong segregation phenomenon in Ti 3+ ion doping. Therefore, the technical difficulty in using the Kyropoulos method to grow large-size high-quality titanium-doped sapphire crystals lies in controlling the doping uniformity and the stable existence of Ti 3+ ions during the growth process.

[0004] The invention patent with the publication number CN104357904B discloses a method for growing titanium sapphire crystals in the cladding by placing a seed crystal at the center of the bottom of a crucible and controlling the temperature of the seed crystal at the bottom of the crucible and the power of the heater. High-quality large-size titanium sapphire crystals with a diameter of 200-250 mm can be achieved. However, it is prone to thermal field pollution, and the thermal insulation performance of the thermal field is unstable, which will directly affect the single crystal property and uniformity of the crystal and is not suitable for growing crystals with a diameter greater than 300 mm. The invention patent with the publication number CN111074337B discloses a method and device for growing high-concentration titanium-doped sapphire crystals by the edge-defined film-fed growth (EFG) method. The EFG method can grow crystals with a fixed shape by designing the mold shape. Although the titanium doping concentration is increased, it is difficult to control crystal growth when growing large-size crystals, and high-quality crystals cannot be grown.

[0005] Therefore, there is a need to study a method for growing large-size titanium-doped sapphire crystals by the Kyropoulos method to ensure low-defect, single-crystal property and uniformity of the crystals. Summary of the Invention

[0006] Aiming at the technical shortcomings of the existing Kyropoulos method for growing large-size titanium-doped sapphire crystals, the present invention provides a method for growing large-size titanium-doped sapphire crystals by the Kyropoulos method. The method includes steps of raw material preparation and loading, heating up to melt the material, adjusting the temperature to initiate crystal growth, crystal growth, crystal cooling in-situ annealing, and wafer H2 annealing. The present invention uses high-purity graphite materials to construct the thermal field, reducing thermal field pollution, precisely controlling the temperature distribution through a double-heating body, and forming a stable temperature gradient field; introducing a mixed gas of Ar and CO as a protective gas during heating to inhibit adverse reactions in the furnace and maintain the stable existence of Ti 3+ ions in the melt; during the crystal growth process by the Kyropoulos method, the crystal does not contact the crucible, reducing stress concentration, improving crystal uniformity, and achieving the efficient growth of large-size, high-quality, low-defect titanium-doped sapphire crystals to meet the manufacturing requirements of high-end lasers and optical devices.

[0007] The present invention provides a method for growing large-size titanium-doped sapphire crystals by the Kyropoulos method. The thermal insulation structure of the thermal field for crystal growth is composed of a bottom insulation board, an annular insulation cylinder, and an upper insulation board, using a carbon felt material with a graphite coating. The heating structure is composed of a side main heater and a bottom auxiliary heater, using graphite material. The crystal growth method includes the following steps:

[0008] 1) Raw material preparation and loading: Mix titanium dioxide powder and aluminum oxide powder evenly, with the mass percentage of mixed titanium dioxide being 0.2-0.6%, and then obtain a titanium-doped aluminum oxide sintered ingot through roasting, and perform filling after crushing treatment;

[0009] 2) Heating up to melt the material: Introduce a mixed gas of Ar and CO as a protective gas, with the volume fraction of CO being 4.5-7.0% and the rest being Ar, and heat up to melt the raw materials;

[0010] 3) Temperature adjustment and seed crystal introduction: After the raw materials are completely melted, wait for the temperature to continue to rise until it is 10 - 18 °C higher than the temperature at which the raw materials are completely melted. At this time, strong convection appears due to the superheating of the melt. Then, reduce the heating power to make the temperature of the melt surface 2048 - 2053 °C. Lower the seed crystal to contact and erode the liquid surface to start crystal growth;

[0011] 4) Crystal growth: Control the crystal growth rate to be 0.2 - 0.5 mm / h. After the crystal grows to the required size, lift it out of the melt;

[0012] 5) In-situ annealing of crystal cooling: Increase the CO concentration in the mixed gas, where the volume fraction of CO is 9.5 - 14.5%. At the same time, carry out cooling and annealing treatment. After the temperature in the furnace drops to room temperature, take out the crystal, and the crystal diameter is 300 - 350 mm;

[0013] 6) H2 annealing of wafers: Perform high-temperature H2 annealing on the cut wafers.

[0014] Among them, the density of the carbon felt material ≥ 0.15 g / cm 3 , the surface roughness of the graphite coating ≤ 0.1 μm, and the coating thickness ≥ 2 mm.

[0015] Among them, the inner diameter of the annular heat-insulating cylinder is 120 - 200 mm larger than the outer diameter of the crucible.

[0016] Among them, the shape of the graphite heater is an "S" disk shape.

[0017] Among them, in step 1, the mass percentage of titanium dioxide is 0.3 - 0.5%, the purity of titanium dioxide powder ≥ 99.95%, and the purity of alumina powder ≥ 99.995%.

[0018] Preferably, in step 1, the mass percentage of titanium dioxide is 0.35 - 0.45%.

[0019] Among them, in step 1, use a mixer to mix titanium dioxide powder and alumina powder evenly, mix for more than 24 h, load into a cylindrical mold for isostatic pressing, and then obtain a titanium-doped alumina sintered ingot through roasting. Then, break it into two specifications of block materials and fine materials and fill them into a molybdenum crucible.

[0020] Preferably, in step 1, the roasting temperature is 1750 - 1900 °C, hold for 5 - 15 h. Roasting makes the raw materials mix and dope more evenly through solid-phase diffusion reaction.

[0021] Preferably, in step 2, in the mixed gas of Ar and CO, the volume fraction of CO is 5% - 6.5%, preferably 5.5% or 6%, and the gas flow rate is 5 - 8 L / min, preferably 6 L / min or 7 L / min.

[0022] Preferably, in step 2, the heating rate is 40 - 68 °C / h, and the material melting time is 30 - 55 h.

[0023] Preferably, in step 3, the seed crystal is a sapphire seed crystal or a titanium-doped sapphire seed crystal.

[0024] Preferably, in step 3, after the raw materials are completely melted, wait for the temperature to continue to rise until it is 12 - 16 °C higher than the temperature at which the raw materials are completely melted. At this time, strong convection appears due to the superheated melt, making the raw materials form a uniformly distributed melt. Then, reduce the heating power. When the temperature of the melt surface is 2051.8 - 2052.8 °C, lower the seed crystal to contact and erode the liquid surface, and wash away the impurities and polycrystals on the lower end face of the seed crystal. Then, reduce the heating power again. When the temperature of the melt surface reaches 2048.2 - 2050.2 °C, start crystal growth.

[0025] Preferably, in step 4, the crystal growth rate is 0.25 - 0.45 mm / h, and more preferably 0.3 - 0.4 mm / h.

[0026] Preferably, in step 5, increase the CO concentration in the mixed gas, where the volume fraction of CO is 10.0 - 12.0%, preferably 10.5%, 11% or 11.5%, increase the reducing atmosphere in the furnace, and can effectively inhibit Ti 3+ ions from being oxidized to Ti 4+ ions, and improve the crystal uniformity.

[0027] Preferably, in step 5, perform a cooling and annealing treatment at a rate of 11.2 - 16.2 °C / h, preferably 12 °C / h, 13 °C / h, 14 °C / h, 15 °C / h or 16 °C / h.

[0028] Preferably, in step 6, perform a high-temperature H2 annealing on the cut wafer, with a heating rate of 55 - 185 °C / h, an annealing temperature of 1800 - 1900 °C, a holding time of 10 - 50 h, and a cooling rate of 45 - 135 °C / h.

[0029] Preferably, in step 6, perform a high-temperature H2 annealing on the cut wafer, with a heating rate of 75 - 155 °C / h, an annealing temperature of 1820 - 1860 °C, a holding time of 20 - 40 h, and a cooling rate of 55 - 115 °C / h, to promote the reduction of Ti 4+ ions to Ti 3+ ions, increase the proportion of Ti 3+ ions, and improve the crystal quality factor, that is, the quality factor value.

[0030] The beneficial effects of the present invention are:

[0031] (1) Produce large-sized high-quality titanium-doped sapphire crystals: Grow large-sized titanium-doped sapphire crystals with a weight of 100 - 145 kg, a diameter of 300 - 353 mm, and a height of 350 - 450 mm. The crystals have high crystallinity. Combining with the high-temperature hydrogen annealing process further promotes the reduction of Ti 4+ to Ti 3+ ions. At the same time, high-temperature annealing can also effectively improve the crystal uniformity, reduce crystal defects, avoid affecting its application effect in fields such as lasers due to uniformity problems, and the figure of merit is greater than 150, thereby improving its application value in fields such as lasers;

[0032] (2) Improve the crystal growth temperature field environment: When using the Kyropoulos method to grow large-sized titanium-doped sapphire crystals, the thermal field requires extremely high stability. Design a "fully carbon" graphite thermal field, which has no deformation, low cost, and good heat preservation performance. It can avoid abnormal temperature gradients and instability of the solid-liquid interface caused by thermal field deformation, and solve the problems of easy deformation of traditional metal thermal fields and volatilization pollution of metal-zirconia thermal fields; Use a double-graphite heating body (side main heater and bottom auxiliary heater) to control independently respectively, replacing the single heating body structure of the traditional Kyropoulos method. Through the cooperation of the double heating bodies, regulate the temperature field and melt flow field in the crystal growth furnace, and maintain the stability of the small temperature gradient and "micro-convex" solid-liquid interface required for the growth of titanium-doped sapphire crystals;

[0033] (3) Precisely control the gas ratio: During the crystal growth process, use a mixed atmosphere of Ar and CO to replace the traditional vacuum crystal growth or single-Ar protective atmosphere crystal growth process technology. Through the adjustment of the mixed atmosphere component parameters in the present invention, the pollution of the melt and crystal by the volatilization of carbon at high temperature is reduced, and the growth rate and quality of the crystal are effectively controlled. On the other hand, the weakly reducing mixed atmosphere of Ar and CO in the furnace can also effectively inhibit the oxidation of Ti 3+ ions to Ti 4+ ions;

[0034] (4) Higher doping concentration: By strictly controlling the doping ratio of titanium ions at 0.2 - 0.6%, controlling the doping uniformity and purity in the raw material preparation process. After the raw materials are completely melted, the liquid surface temperature rises, causing strong convection due to the overheating of the melt, which can improve the doping mixing uniformity of the melt at high temperature; Using a graphite thermal field and combining with the Kyropoulos method for crystal growth to provide a stable temperature environment, the segregation phenomenon of Ti 3+ ion doping in the melt is weakened, ensuring the stable growth of the crystal under high doping concentration;

[0035] Generally speaking, compared with the prior art, the present invention not only improves the performance and quality of large-sized titanium-doped sapphire crystals, but also improves the controllability and stability of its preparation process, showing significant superiority. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1Process flow chart for growing large-sized titanium-doped sapphire crystal

[0037] Figure 2 Schematic diagram of the structure of the crystal growth thermal field

[0038] Among them, 1 is the upper thermal insulation plate, 2 is the annular thermal insulation cylinder, 3 is the bottom thermal insulation plate, 4 is the side main heater, and 5 is the bottom auxiliary heater Specific implementation mode

[0039] The present invention will be further described in detail below in conjunction with the specific implementation mode to better reflect the advantages of the present invention

[0040] Example 1 is as follows

[0041] A method for growing large-sized titanium-doped sapphire crystal by the Kyropoulos method. The thermal insulation structure of the thermal field for crystal growth is composed of the bottom thermal insulation plate 3, the annular thermal insulation cylinder 2 and the upper thermal insulation plate 1. The carbon felt material with a graphite coating is used, the surface coating roughness ≤ 0.1μm, the coating thickness ≥ 2mm, and the inner diameter of the annular thermal insulation cylinder is 610mm (the outer diameter of the crucible is 450mm); the heating structure is composed of the side main heater 4 and the bottom auxiliary heater 5, which are independently controlled respectively to adjust the heating power. The heater is made of hard graphite material and has an "S" disk shape. Among them, the density of the thermal insulation carbon felt thermal field material ≥ 0.15g / cm 3 , see the schematic diagram of the thermal field structure Figure 2 , this crystal growth method is as Figure 1 shown, and mainly includes the following steps

[0042] 1) Raw material preparation and loading: According to the doping mass percentage of 0.35%, weigh 420g of titanium dioxide powder with a purity ≥ 99.95% and 119.58kg of alumina powder with a purity ≥ 99.995%, put them into a mixer and mix for 28h; load them into a cylindrical mold for isostatic pressing, and then carry out roasting. The roasting temperature is 1820°C and the roasting time is 10h; obtain 75kg of block materials by hitting the titanium-doped alumina sintered ingot, and then obtain 45kg of fine materials by crushing the remaining raw materials; fill 120kg of raw materials into a molybdenum crucible and install 1 sapphire seed crystal to complete the furnace combination

[0043] 2) Heating and melting the materials: When heating, introduce a mixed gas of Ar and CO as the protective gas, the volume fraction of CO is 5.0%, the gas flow rate is 7L / min, the heating rate is 45 - 55°C / h, the melting power is 40.2kW, and the melting time is 35h

[0044] 3) Temperature adjustment and seeding: After the raw materials are completely melted, wait for the temperature to rise by 15 °C above the complete melting temperature to cause strong convection in the superheated melt, then reduce the power. When the temperature of the melt surface is 2052.0 - 2052.4 °C, lower the seed crystal to contact and erode the liquid surface, melt and wash away the impurities and polycrystals on the lower end face of the seed crystal, and then reduce the power to make the liquid surface temperature 2049.0 - 2049.5 °C, and start crystal growth;

[0045] 4) Crystal growth: Monitor the crystal to grow at a growth rate of about 0.3 mm / h. When the crystal height reaches 400 mm, lift it out of the melt;

[0046] 5) In-situ annealing during crystal cooling: Increase the CO concentration in the mixed gas, with the CO volume fraction being 10.0%. The crystal stops in place and undergoes cooling annealing treatment at a rate of 12.2 - 14.2 °C / h. When the furnace temperature drops to room temperature, open the furnace and take out the crystal;

[0047] 6) H2 annealing of wafers: After cutting, large wafers with a diameter of 308 mm and a thickness of 30 mm without bubble defects are obtained. The processed wafers are subjected to high-temperature H2 annealing. The heating rate is 65 - 95 °C / h, the annealing temperature in the H2 atmosphere is 1850 °C, the holding time is 20 h, and the cooling rate is 55 - 80 °C / h.

[0048] The titanium-doped sapphire crystal grown in this example weighs 111.35 kg. Visually observed, there is no polycrystal, the crystal has few bubbles, a deep red chromaticity, small reaction ash in the furnace, and no impurity attachment on the crystal shoulder surface; By detecting the processed wafers, the dislocation density is 395 / cm 2 , the figure of merit value is 175, and the uniformity is good.

[0049] The comparative example 1 is as follows:

[0050] A process for growing large-size titanium-doped sapphire crystals by the Kyropoulos method, using a traditional tungsten metal thermal field, and the process steps are as follows:

[0051] 1) Raw material preparation and loading: The same as in Example 1;

[0052] 2) Heating and melting the material: When heating, introduce a mixed gas of Ar and CO as the protective gas, with the CO volume fraction being 5.0%, the gas flow rate being 7 L / min, the heating rate being 45 - 55 °C / h, the melting power being 44.6 kW, and the melting time being 41 h;

[0053] 3) Temperature adjustment and seeding: The same as in Example 1;

[0054] 4) Crystal growth: The same as in Example 1;

[0055] 5) In-situ annealing during crystal cooling: The same as in Example 1;

[0056] 6) Wafer H2 annealing: After cutting, a large wafer with a diameter of 152 mm and a thickness of 23 mm without bubble defects was obtained. The annealing process was the same as that in Example 1.

[0057] The titanium-doped sapphire crystal grown in this comparative example weighed 112.11 kg. Visually observed, there was more than 20% polycrystal, many crystal cluster bubbles, medium red chromaticity, a large amount of reaction ash in the furnace, and impurities adhered to the crystal shoulder surface; by detecting the processed wafer, the dislocation density was 450 / cm 2 , the figure of merit value was 93, and the uniformity was poor.

[0058] In Comparative Example 1, a metal thermal field was used to grow a large-size titanium-doped sapphire crystal by the Kyropoulos method. The melting power was higher than that of the graphite thermal field, indicating that the metal thermal field had poor heat preservation and insufficient thermal stability. The thermal field reaction volatilization pollution was relatively serious, which affected the crystal quality. Affected by polycrystal and crystal cluster bubbles, the diameter of the processed product was less than 200 mm, and the figure of merit value was less than 100.

[0059] Comparative Example 2 is as follows:

[0060] A process for growing a large-size titanium-doped sapphire crystal by the Kyropoulos method, using the same thermal field structure as in Example 1. The process steps are as follows:

[0061] 1) Raw material preparation and loading: The same as in Example 1;

[0062] 2) Heating and melting the material: High-purity argon was introduced as a protective gas during heating, the gas flow rate was 7 L / min, the heating rate was 45 - 55 °C / h, the melting power was 40.0 kW, and the melting time was 33 h;

[0063] 3) Temperature adjustment and seeding: The same as in Example 1;

[0064] 4) Crystal growth: The same as in Example 1;

[0065] 5) Crystal cooling and in-situ annealing: Keeping the high-purity argon atmosphere unchanged, the crystal was cooled and annealed at a rate of 12.2 - 14.2 °C / h in situ, and the furnace temperature was cooled to room temperature and the crystal was taken out of the furnace;

[0066] 6) Wafer H2 annealing: After cutting, a large wafer with a diameter of 184 mm and a thickness of 20 mm without bubble defects was obtained. The annealing process was the same as that in Example 1.

[0067] The titanium-doped sapphire crystal grown in this comparative example weighed 111.85 kg. Visually observed, there was no polycrystal, many through-crystal bubbles, medium red chromaticity, a large amount of reaction ash in the furnace, and impurities adhered to the crystal shoulder surface; by detecting the processed wafer, the dislocation density was 472 / cm 2 , the figure of merit value was 75, and the uniformity was poor.

[0068] Comparative Example 2 uses a graphite thermal field, purifies argon gas, and grows large-sized titanium-doped sapphire crystals by the Kyropoulos method. The melting power is equivalent to that of Example 1, indicating that the furnace atmosphere has little effect on the heat preservation of the thermal field. However, the thermal field reaction volatilization pollution is relatively serious, which affects the crystal quality. Affected by the through-bubble in the crystal, the diameter of the processed product is less than 200 mm, and the quality factor value is less than 100.

Claims

1. A method for growing large-sized titanium-doped sapphire crystals by the Kyropoulos method, characterized in that: The thermal insulation structure of the crystal growth heat field is composed of a bottom insulation plate, an annular insulation tube and an upper insulation plate, and adopts a graphite-coated carbon felt material, the density of which is ≥ 0.15g / cm 3 , the graphite coating roughness is ≤0.1μm, the coating thickness is ≥2mm, the heating structure is composed of a side main heater and a bottom auxiliary heater, and the graphite material is used. The crystal growth method includes the following steps: 1) Raw material preparation and filling: Titanium dioxide powder and alumina powder are mixed evenly, wherein the mass percentage of titanium dioxide mixed is 0.2-0.6%, and then roasted to obtain titanium-doped alumina sintered ingots, which are crushed and then filled; 2) Heating the melt: introducing a mixed gas of Ar and CO as a protective gas, wherein the volume fraction of CO is 4.5%-7.0% and the rest is Ar, and heating is increased to melt the raw materials; 3) Temperature adjustment for seeding: After the raw materials are fully melted, wait for the temperature to continue to rise until it is 10-18°C higher than the full melting temperature of the raw materials. At this time, the melt is overheated and strong convection occurs. Then reduce the heating power to make the melt surface temperature 2048-2053°C, and the descending seed crystal contacts the liquid surface for melting and begins crystal growth; 4) Crystal growth: Control the crystal growth rate to 0.2-0.5 mm / h. After the crystal grows to the required size, pull it out from the melt; 5) Crystal cooling in-situ annealing: Increasing the CO concentration in the mixed gas and increasing the reducing atmosphere in the furnace can effectively inhibit Ti 3 + The ions are oxidized to Ti 4+ ions to improve crystal uniformity, wherein the volume fraction of CO is 9.5-14.5%, and a cooling annealing treatment is performed at the same time. After the temperature in the furnace drops to room temperature, the crystal is taken out. The crystal has a diameter of 300-350mm, a height of 350-450mm, and a weight of 100-145kg; 6) Wafer H2 annealing: The cut wafer is subjected to high temperature H2 annealing.

2. A method for growing large-sized titanium-doped sapphire crystals by the kyberyzing method as claimed in claim 1, characterized in that: The inner diameter of the annular heat preservation cylinder is 120-200 mm larger than the outer diameter of the crucible; the shape of the graphite heater is an "S" disk.

3. The method for growing large-sized titanium-doped sapphire crystals by the kyberyzing method as claimed in claim 1, characterized in that: In the step 1, the mass percentage of titanium dioxide is 0.3-0.5%, the purity of titanium dioxide powder is ≥99.95%, and the purity of aluminum oxide powder is ≥99.995%; the calcination temperature is 1750-1900° C. and maintained for 5-15 hours.

4. The method for growing large-sized titanium-doped sapphire crystals by the kyberyzing method as claimed in claim 1, characterized in that: In the step 2, in the mixed gas of Ar and CO, the volume fraction of CO is 5%-6.5%, and the gas flow rate is 5-8 L / min.

5. The method for growing large-sized titanium-doped sapphire crystals by the kyberyzing method as claimed in claim 1, characterized in that: In the step 3, after the raw materials are fully melted, the temperature is allowed to continue to rise until it is 12-16°C higher than the fully melted temperature of the raw materials. At this time, the melt is overheated and strong convection occurs, so that the raw materials form a uniformly distributed melt. The heating power is then reduced. When the melt surface temperature is 2051.8-2052.8°C, the seed crystal is lowered to contact the liquid surface for melting and cleaning the impurities and polycrystalline on the lower end surface of the seed crystal. The heating power is then reduced. When the melt surface temperature reaches 2048.2-2050.2°C, crystal growth begins. The seed crystal is a sapphire seed crystal or a titanium-doped sapphire seed crystal.

6. A method for growing large-sized titanium-doped sapphire crystals by kyberysis as claimed in claim 1, characterized in that: In step 4, the crystal growth rate is 0.25-0.45 mm / h.

7. The method for growing large-sized titanium-doped sapphire crystals by the kyberyzing method as claimed in claim 1, characterized in that: In step 5, the CO concentration in the mixed gas is increased, wherein the CO volume fraction is 10.0-12.0%.

8. The method for growing large-sized titanium-doped sapphire crystals by the kyberyzing method as claimed in claim 1, characterized in that: In the step 5, the temperature is lowered and annealed at a rate of 11.2-16.2° C. / h.

9. The method for growing large-sized titanium-doped sapphire crystals by the kyberyzing method as claimed in claim 1, characterized in that: In step 6, the cut wafer is subjected to high temperature H2 annealing, with a heating rate of 55-185°C / h, an annealing temperature of 1800-1900°C, a holding time of 10-50h, and a cooling rate of 45-135°C / h.

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