Determination of Stoichiometry Variations in LiNbO₃ and LiTaO₃ by Raman Powder Spectroscopy

Abstract

Raman spectroscopy of powders is shown to be a sensitive technique for detecting stoichiometry variations. The method makes use of the broadening of the Raman‐active modes which occurs when the translational symmetry of the lattice is reduced on deviation from simple, fixed cation ratios in the structure. Application of the technique to the LiNbO3(ss) system shows that the room‐temperature solid‐solution range does not exceed 50±0.5 mol% Nb2O5 and that congruent LiNbO3(ss) at 51.4 mol% Nb2O5 is thermodynamically unstable below ≅800°C. Similarly, application of the Raman method to the LiTaO3(ss) system indicates that congruent LiTaO3(ss) at 51.0 mol% Ta2O5 is unstable at temperatures <1000°C. Copyright © 1972, Wiley Blackwell. All rights reserved