無重力環境におけるサマルスカイトの単結晶育成(<特集>無重力下における結晶成長)

抄録

The boule grown under microgravity conditions (Boule S) was 2.7 mm in diameter and 8 mm in length. It was found that Boule S is not a single crystal and composed of 5 phases: (Fe, Ca, Y) Nb_2O_6, (Y, Ca, U) NbO_4, Fe_3Nb_5 O_<16>, Nb_2O_5 and (Y, Ca, Fe, U)_<1-x>NbO_4; x=0.02-0.1. No Samarskite was found in Boule S. These phases are identical with those found in the boule grown on the earth (Boule E). The distribution and the size of each phase was different from those in Boule E. The grains of Nb_2O_5 were found everywhere in Boule E In Boule S, Nb_2O_5 crystallites were found only in a solidified molten zone, not in the boule. On the earth, during the growth, the solution of the molten zone was caught by the crystallized body and became Nb_2O_5 inclusion in Boule E. But the solution was not trapped under microgravity conditions. On the earth, the solution migrated to the grown crystal and covered it. The surface area of the molten zone was enlarged. Accordingly it is difficult to keep the volume of the molten zone constant on the earth. On the other hand, under microgravity conditions, the volume could be easily kept constant and the boule with nearly uniform diameter was obtained. This result shows that the composition of the solution can be easily kept constant under microgravity conditions. To keep the composition constant is essential for the growth of a single crystal by the TSFZ method. It has been revealed that the microgravity conditions are suitable environment for the TSFZ method. A large bubble was observed in Boule S. Its diameter was larger than a half of the diameter of Boule S. On the earth, due to buoyancy, bubbes gather at the upper part of the molten zone. Accordingly, bubbles are seldom trapped in the crystal grown by the floating zone method. While under microgravity conditions, bubbles grew larger and spoiled quality of the grown crystal. The study of the formation and the movement of bubbles in oxide solution is necessary to grow a high quality oxide crystal under microgravity conditions.