Growth of noncongruent LiTaO₃ crystal by chemical vapor phase equilibration using niobium-based two-phase powder

Noncongruent nearly stoichiometric/lithium-deficient LiTaO₃ crystal was grown by lithium-rich/lithium-deficient chemical vapor-phase-equilibration (VPE) technique, and low-cost two-phase powder LiNbO₃-Li₃NbO₄ or LiNbO₃-LiNb₃O₈ instead of expensive LiTaO₃-Li₃TaO₄ or LiTaO₃-LiTa₃O₈ was used in the VPE experiments. The LiTaO₃ crystalline phase in the lithium-rich/lithium-deficient crystal was confirmed by X-ray analysis. The lithium-rich/lithium-deficient VPE-induced lithium-oxide (Li₂O) molar content increase/reduction was measured as a function of VPE duration using gravimetric method, and empirical relations between them are presented for both cases. We show that both the lithium-rich and lithium-deficient VPE techniques based on the two-phase powder LiNbO₃-Li₃NbO₄ or LiNbO₃-LiNb₃O₈ can be successfully used to adjust the lithium-oxide content in a LiTaO₃ crystal and produce a noncongruent nearly stoichiometric or lithium-deficient crystal plate with desired lithium-oxide content.