大尺寸金红石(TiO_2)单晶体生长条件的实验研究

Experimental Study on Growth Conditions of Big-bulk Rutile Crystal

采用高纯(99.995%)、超细的金红石(TiO2)粉末为起始原料,用燃熔法制备了尺寸为30mm×50mm的金红石(TiO2)单晶体。讨论了生长气氛、生长速度、温度梯度在晶体生长中的作用,对比了晶体在空气中与在氧气中退火的结果,测定了晶体试样的摇摆曲线和透过率,并与商用晶体的透过率进行了比较。实验表明:生长气氛中的氧分压大于液固界面(即生长界面)处熔体的氧离解压是生长完整晶体的必要条件;在此条件下,能否生长为大尺寸晶体则取决于炉膛的轴向温度梯度;晶体在退火过程中可消除热应力,但退火更重要的作用是通过氧化反应消除氧空位,在氧气氛中退火,可明显缩短退火时间;所制备的晶体完整性较好,透过率与商用晶体基本一致。

Big-bulk rutile single crystal (30mm×50mm) was grown successfully by the flame fusion method using high pure (99.995%) ultrafine TiO_2 powder as original material. The effects of growth atmosphere, growth rate and temperature gradient on crystal growing were discussed. The annealing results between in air and in oxygen were compared. Swing curve and transmissibility of the sample were measured, comparing its transmissibility with that of commercial crystal. It was made clear that the growth atmosphere with higher oxygen partial pressure than that of oxygen's decomposed pressure at the liquid-solid interface is a necessary condition of the perfect crystal growth, that in this case, it depends on the axial temperature gradient of the furnace whether a large-sized single crystal can be obtained or not.The more important role of annealing is the oxidization reaction to eliminate oxygen vacancies and the annealing time can be considerably shortened in oxygen. The as-grown crystal has almost perfect structure and its transmissibility is nearly close to that of commercial crystal.