Coexistence of Li and Nb vacancies in the defect structure of pure LiNbO3 and its relationship to optical properties

We present a model of the structure of intrinsic defects in lithium niobate, which is based upon the coexistence of both lithium and niobium vacancies. The contents of the various kinds of intrinsic defects were thus determined as a function of the composition in off-congruent crystals. The comparison with phonon characteristics drawn from Raman data pointed out the validity of our description of the defect structure with dominant lithium vacancies. Anomalies in the dependencies of electro-optical properties on the crystal composition can be explained within the model. This reinforces the reliability of our model and calculations. (orig.)