COMPOSITIONAL UNIFORMITY IN GROWTH AND POLING OF LARGE-DIAMETER LITHIUM-NIOBATE CRYSTALS

An experimental study was performed of compositional uniformity in growth and poling of large-diameter lithium niobate crystals. Crystal compositions were characterized through Curie temperature measurement and phase-match temperature measurement for non-critical 1.06-mu-m frequency doubling. Methods were established and tested for preparing crystal growth melts of controlled stoichiometry specifiable to within 0.01 mol% Li2O. A previously unreported congruent composition value of 48.38 +/- 0.015 mol% Li2O was determined. Near the congruent composition, a strong influence was observed of melt stoichiometry on the domain structure of as-grown crystals. The effects of post-growth poling on compositional distribution were studied. Effective poling conditions having unmeasurable influence on crystal composition were established. Use of a congruent melt was observed to enable growth of clear uncracked crystals representing melt fractions as large as 98%. Crystals representing 85% melt fractions were routinely grown having compositional uniformity of +/- 0.003 mol% Li2O. Lithium niobate crystalline material produced through the combination of congruent growth and preferred poling conditions was observed to enable improved acoustical and optical device performance.