ELECTROOPTIC PROPERTIES IN UNDOPED AND CR-DOPED LINBO3 CRYSTALS

We have investigated the electro-optic and dielectric properties of Li NbO3 along the ferroelectric c axis in pure and chromium-doped crystal s. We have studied four series of samples with various crystal composi tions and doping concentrations to separate the influence of the intri nsic defects related to the non-stoichiometry and the effect of the in troduction of chromium. In pure and slightly doped crystals, the elect ro-optic coefficient r(c), shows a non-monotonous dependence on the co ntrolled crystal composition, which reflects a similar behaviour of th e corresponding dielectric permittivity. In the highly Cr-doped crysta ls r(c), displays a large decrease with increasing Cr concentration wh atever the crystal composition. The results have been discussed by mea ns of the LiNbO3 structure and the substitution site dynamics.