Crystal growth of Ca₁₂Al₁₄O₃₃ by the floating zone method

We have grown single crystals of Ca₁₂Al₁₄O₃₃ (C12A7), a congruently melting compound, by the floating zone method. With the conventional method, the shape of the solid-liquid interface was concave, and many bubbles and cracks remained in the grown crystal. To reduce them, the crystal growth at a lower growth rate and the control of the shape of the solid-liquid interface were examined. For the growth rate <0.3 mm/h, the amount of bubbles was reduced considerably. However, in such a condition, a significantly large bubble was often formed in the molten zone, which disturbed the stability of the molten zone. Introducing an alumina tube as a heat reservoir at a suitable position in the heated area, the shape of the solid-liquid interface could be changed from concave to a convex one. This may suggest that the effect of the concave interface could be eliminated and crystals with high quality may be grown at a higher growth rate.