Progress in single crystal growth of LiNbO3 using double crucible Czochralski method

In order to grow singled crystals with high quality and high homogeneity from off-congruent melts, a double crucible Czochralski method has been developed. In this method, the melt was divided into two parts by a double structure (two chamber system) crucible. The crystal was grown from the inner melt, and powder with the same composition as the growing crystal was supplied to the outer melt. The powder was supplied smoothly at the rate of weight increase of the growing crystal. This rate was automatically controlled to match the weight increase of the growing crystal as monitored by a load cell. In combination with an automatic diameter control system, a fully automatic double crucible Czochralski method was established. Using this method, LiNbO3 single crystals with a composition close to stoichiometric were grown, and their photorefractive properties were compared with those of Nb-rich congruent melt LiNbO3 crystals. Two beam coupling experiments show that both non-doped and Fe-doped stoichiometric crystals exhibited larger exponential gain coefficients than the exponential gains obtained in Fe-doped congruent crystals. This fact suggested that nonstoichiometry control of LiNbO3 is a key for improvement of these properties.