STOICHIOMETRY ISSUES IN SINGLE-CRYSTAL LITHIUM TANTALATE

Stoichiometry issues in lithium tantalate were studied through Czochra lski growth of single crystals and vapor transport equilibration (VTE) of crystalline samples to specified Li/Ta compositions. Crystals were characterized through measurement of the ferroelectric Curie temperat ure T-c. The VTE experiments indicated a linear variation of T-c with Li/Ta ratio across the investigated range of 47.5-49.5 mol% Li2O. By c ontrol of initial melt stoichiometry, crystals representing melt fract ions > 90% were grown having compositional uniformity within +/- 0.015 mol% Li2O. Growth of the compositionally uniform crystals was determi ned to take place through incongruent solidification, with lithium rej ection from the growth interface compensating for Lithium volatilizati on from the melt surface. With the growth process applied, a melt comp osition of 48.39 mol% Li2O yielded grown crystals of a uniform 47.85 m ol% Li2O solid composition. The lithium tantalate congruent compositio n was determined to lie at a value less than or equal to 47.70 mol% Li 2O. (C) 1995 American Institute of Physics.