Growth Conditions of Subgrain-Free LiNbO₃ Single Crystals by the Czochralski Method

Subgrain-free LiNbO 3 single crystals were grown by the CZ method. It is generally accepted that thermal fluctuations are a serious drawback in growing a high-quality crystal. However, we found that subgrain-free LiNbO 3 crystals could be grown only under regular thermal fluctuation of the melt. In order to analyze the effect of thermal fluctuation, we measured such properties of molten LiNbO 3 as the viscosity, density, surface tension, and electrical conductivity. From these measurements, we speculate the existence of clusters made of niobium oxide molecules and lithium oxide molecules below 1280°C. The volume fraction of these clusters decreases as the temperature of molten LiNbO 3 increases. A reduction of the density of these clusters prevents LiNbO 3 crystals from producing subgrains. This reduction is regarded as one of the necessary conditions required for growing a subgrain-free LiNbO 3 single crystal.