Band structure treatment of the influence of nonstoichiometric defects on optical properties in LiNbO3

We present a band structure approach in connection with a molecular dynamics cluster optimization that accounts for various structural modifications related to the nonstoichiometry of LiNbO3 crystals. Variation of optical properties with the deviation from the stoichiometric composition can be understood within this approach. The particular role of the electron-phonon contributions to the electro-optic coefficient is shown. Model calculations yield a large dependence of the electro-optic coefficient r22 on the crystal composition, in agreement with the experimental data. The observed minimum of the r22 coefficient versus nonstochiometry is explained within a microscopic approach. The r33 tensor component shows substantially different behavior versus the stoichiometry.