不定比組成を制御した中間化合物単結晶育成 : 希土類ガーネットの不定比組成を例として

抄録

Some kinds of binary oxide compounds used for the optical applications as single crystals exhibit common nonstoichiometric natures. The melt of eutectic composition at nonstoichiometric component deficient side coexist in equilibrium with the crystal of chemical composition close to the stoichiometry. On the basis of this point, a model for single crystal growth from the melt near the eutectic point is proposed by using the travelling solvent floating zone method in order to control nonstoichiometry. NdGG (Nd_<3+χ>Ga<_5-χ>O<_12>) single crystal grown by this method has a lattice constant of 12.505Å which is close to that of the stoichiometric composition (12.504Å). Moreover, it is revealed from polarizing microscopic observation that the compositional variation due to the nonstoichiometry has been diminished in the NdGG crystal. This result is contradictory to the usual consideration based on the BPS model where any variations in growth conditions will lead to compositional variations if such nonstoichiometric crystals are grown at other than the congruently meling composition.