Stoichiometry Issues in Single-Crystal Lithium Tantalate

Reprinted with permission from P.F. Bordui, R.G. Norwood, C. D. Bird, and J. T. Carella, Journal of Applied Physics, 78, 4647-4650, (1995). American Institute of Physics.

Abstract

Stoichiometry issues in lithium tntalate were studied through Czochralski 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 temperature 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 control of initial melt stoichiometry, crystals representing melt fractions >90% were grown having compositional uniformity within ±0.015 mol % Li₂O. Growth of the compositionally uniform crystals was determined to take place through incongruent solidification, with lithium rejection from the growth interface compensating for lithium volatilization from the melt surface. With the growth process applied, a melt composition of 48.39 mol % Li₂O yielded grown crystals of a uniform 47.85 mol % Li₂O solid composition. The lithium tantalate congruent composition was determined to lie at a value less than or equal to 47.70 mol % Li₂O.