Abstract
Suitable conditions in LiNbO_3 (LN) single crystal growth by the continuous charging Czochralski (CC-CZ) method were studied, such as the thermal field affected by the vertical position of the inner partition cylinder, mixing situation of the charged material with the melt by means of Fe_2O_3 addition as a tracer and temperature fluctuation in melt affected by the particle size of the charging material. The LN crystal grown from 60 mol% Li_2O melt was annealed in air. Li_3NbO_4 phase appeared as precipitate in the LN. The fact suggests that the Li-sufficient boundary of LN solid solution range is not vertical straight line but curve line toward the Li-deficient side such as the Li-deficient boundary in the phase diagram of the Li_2O-Nb_2O_5 system. The effective nonliner optical coefficient increased as Li content in melt increased. The photore-fraction dependence on Li content in melt with the range from 48.6 to 60 mol% Li_2O was investigated. Birefringence change had a maximum value at 58 mol% Li_2O in melt, which was near the stoichiometric composition. The dependence was not changed by annealing treatment. Therefore the photorefraction depend on the photoconductivity caused by vacancies rather than the Glass constant in the Li-rich melt range.
