Structural defects in congruent and near-stoichiometric LiNbO3

A. comparative study of LiNbO3 single crystals with congruent and near-stoi chiometric compositions was performed using hyperfine interactions and ion beam techniques. Our data show that the structure of congruent LiNbO3 canno t be completely described by the models which assume only vacancies and Nb antisites. Additional disorder has to be considered both at the Li and Nb s ites. The additional defects are cation stacking inversions, in which the c ation sequence coincides locally with the one of ilmenite-like LiNbO3. We s uggest that these stacking inversions are associated with the Nb antisites necessary for charge compensation in Li-deficient material.