PREPARATION AND CHARACTERIZATION OF OFF-CONGRUENT LITHIUM-NIOBATE CRYSTALS

Vapor transport equilibration was used to prepare lithium niobate crystals of a variety of controlled off-congruent compositions. Crystals were characterized through measurement of the ferroelectric Curie temperature T(c) and measurement of the temperature for noncritical phase matching T(PM) of second-harmonic generation from both 1.064- and 1.32-mu-m laser sources. Across the majority of the single-phase region, both T(c) and T(PM) were observed to vary nearly linearly with Li/Nb ratio. The variation in T(PM) with Li/Nb ratio was observed to change direction within the single-phase region at some small but finite compositional interval away from the Li-rich phase boundary. Crystals equilibrated to the Li-rich phase boundary had excellent optical homogeneity. Preparation of Li-poor crystals was hampered by extremely slow lithium diffusivity and problems with second-phase precipitation.