Theoretical study of temperature dependence of spontaneous polarization, optical properties and linear electro-optic coefficients of tetragonal KNbO₃

The microscopic mechanisms of refractive indices, birefringence, spontaneous polarization and linear electro-optic effects are examined for KNbO 3 using a microscopic model which takes into account a quantum method based upon the orbital approximation and the dipole-dipole interaction due to the local field acting on the constituent ions. It is found that the electronic polarizabilities play a major role in these calculations and that the birefringence n and the linear electro-optic coefficients are in good agreement with the experimental data.