Growth of Bi12GeO20 Single Crystals by the Pulling-Down Method with a Continuous Powder Feed System

Transparent and crack-free Bi12GeO20 single crystals have been grown by the pulling-down method with a continuous powder feed system. Bi-rich feed powder having a composition of 14.1mol% GeO2 is favorable to obtain stoichiometric crystals. Striation-free crystals with an increased transmittance are grown under a small temperature gradient. The shape of the solid-liquid interface during the crystal growth is nearly flat, which is advantageous to avoid core formation. Average dislocation density is estimated to be 2×104/cm2, which is comparable to that of Bi12GeO20 crystals grown by the conventional Czochralski method