Electro-optic effect in SrTiO$_{3}$ and Sr$_{1-x}$Ca$_{x}$TiO$_{3}$ ($x$ = 0.014)

The results of the investigation of the quadratic electro-optic effect in Sr$_{1-x}$Ca$_{x}$TiO$_{3}$ with $x$ = 0.014 (SCT) and in nominally pure SrTiO$_{3}$ (STO) at room temperature in applied direct-current (dc) and alternating-current (ac) electric fields have been presented. It has been shown that the quadratic (in polarization) electro-optic coefficients of STO and SCT crystals coincide within the accuracy of the determination ($\pm$ 5%). It has been found that, in nominally pure STO measured in a dc electric field, there is a relaxation of the electro-optic effect with a relaxation time $\tau\approx$ 30 s due to the formation of a space charge in the sample. No similar effect in SCT has been observed. A possible mechanism for the formation of a space charge in STO and SCT has been discussed.