Temperature variations of the refractive index fen. have been studied in single crystals of ferroelectric perovskites with diffuse phase transitions, with a different degree of ordering and also in the nonferroelectric crystals with pyrochlore-type structure. Ferroelectric contributionto the index of refraction was obtained in ferroelectric perovskites. In all these compounds the temperature behaviour of (TnfCO above Tc was found to vary in a same manner and this behaviour was interpreted in terms of local polarization in microregions with different transition temperatures. Contrary to that ScCtJ) around T behaves differently in ferroelectrics with diffuse phase transitions and in ferroelectrise with a different degree of ordering, that can. be undestood within the framework of percolation model.