An Improvement on Skull-Melting Method for Growing Sapphire Single Crystal
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摘要: 早先文献中曾报道，壳熔法熔化蓝宝石时，由于出现“去耦”现象，不能长时间地保持蓝宝石熔体稳定的熔化状态，熔体倾向于在一段时间(3～4h)后缓慢地“去耦”，即减弱熔体与电磁场的耦合程度而自发地凝固，故无法进行正常的定向结晶而生长出较大的晶体。通过具体的壳熔法生长蓝宝石晶体实验找到了减弱和防止“去耦”现象出现的方法，壳熔法设备的参数是：射频电源频率为0.8～1.8MHz，电源额定功率为100 kW，冷坩埚内径为200mm，坩埚下降速度为3～10mm/h。并从理论上分析了出现“去耦”现象的原因，进而改进了壳熔法蓝宝石晶体生长工艺，采用壳熔定向结晶法，第一次得到了厘米级蓝宝石单晶。与壳熔法生长立方氧化锆晶体的情况相比，壳熔法生长的晶体材料可以分成二类：一类材料在熔点上下的电阻率都比较小(1～0.1Ω·cm量级，导电体)；另一类材料在熔点之下的电阻率比较大(104Ω·cm量级，介电体)，在熔点之上的电阻率急剧减小(0.1Ω·cm量级，导电体)。这二类材料在用壳熔法生长晶体时有很多不同的特点，有待深入研究。Abstract: Some researches shows that because of“de－couple”phenomena，skull－melting method was not able to keep the stable melting state of sapphire for long time.The melting sapphire tended to slowly de－couple，which weakens the coupling between the melting sapphire and the electromagnetic field，and then the melting sapphire freezes spontaneously in 3 to 4 hours which destroys normal directional crystallization.So，this paper analyzed the possible causes of“de－couple”and made some improvement in this field of study.The author got the sapphire crystal in cm－level for the first time with the skull－melting directional crystallization method.Parameters of skull－melting method are as follows：RF power frequency is 0.8—1.8MHz，RF output power is 100kW，inner diameter of cold crucible is 200mm and drop speed of cold crucible is 3—10mm/h.Compared with the cubic zirconia(CZ)crystal grown by skull－melting method，the materials，produced with skull－melting method，can be divided into two groups：one is“conductor”with low resistivity(the level of 1—0.1Ω·cm)before and after melting；another is dielectric with high resistivity(the level of 104Ω·cm)before melting which then turned into“conductor”with low resistivity(the level of 0.1 Ω·cm)after melting.These two groups of materials have a lot of different crystal growth characteristics worthy of doing further researches.
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Keywords:
- crystal growth /
- skull-melting technique /
- sapphire /
- single crystal
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