Influence of Parameters in Vapor Transport Equilibration Treatment on Composition and Homogeneity of LiTaO3 Single Crystals

The effect of key parameters such as time, temperature, and equilibration powder concentration in vapor transport equilibration (VTE) treatment on the Li2O content of initially congruent X-, Y-, and Z-cut LiTaO3 crystals is experimentally investigated. The Li2O content across the thickness of the crystal is estimated by Raman spectroscopy with accuracy of 0.05-0.15 mol%. The Li2O loss from equilibration powders has been monitored as a function of treatment temperature and duration. The results show that the Li2O content in the crystal nonlinearly depends on the equilibration powder composition and that homogeneous stoichiometric LiTaO3 crystals can be obtained by treatment for at least 36h at 1250 degrees C in Li2O-rich atmosphere, created by powders containing >54 mol% of Li2O. The anisotropic Li+ diffusion coefficients and its activation energy are also experimentally estimated. Finally, the VTE conditions are defined for the production of different cuts of LiTaO3 crystals with controlled homogeneous Li2O nonstoichiometry in the range from subcongruent to stoichiometric compositions.