The Raman spectra of 3 pure crystals having differing Li contents, and of several doped (Mg, In, Ti) crystals, were investigated. A weak peak at about 738/cm, reported as being a very strong Raman peak of the ilmenite phase, was observed in non-stoichiometric crystals. The dependence of this peak, upon the Li content and dopant concentration, suggested that there was a new type of defect structure which had an ilmenite-like stacking and a direct relationship to the antisite NbLi4+ ion. This proved experimentally the existence of an ilmenite-like stacking defect in non-stoichiometric LiNbO3 for the first time. This defect was in good agreement with the Li-vacancy model, and had a different structure to that previously proposed.

Ilmenite-Like Stacking Defect in Non-Stoichiometric Lithium Niobate Crystals Investigated by Raman Scattering Spectra. Y.Kong, J.Xu, X.Chen, C.Zhang, W.Zhang, G.Zhang: Journal of Applied Physics, 2000, 87[9], 4410-4