Preparation and Characterization of Off-Congruent Lithium Niobate Crystals

Reprinted with permission from P.F. Bordui, R.G. Norwood, D. H. Jundt, and M. M. Fejer, Journal of Applied Physics, 71, 875-879, (1992). American Institute of Physics.

Abstract

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-µm 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.