Optical and dilatometric manifestations of phase transitions in K2SeO4 crystal

Temperature dependencies of the characteristic optical paths difference D(T) of K2SeO4 crystal in the range of 80-295 K were measured using the Jamen type interferometer. Significant anomalies of D(T) dependencies in the vicinity of incommensurate-paraelectric phase transition (T-i = 130 K) are observed. On the basis of D(T) temperature dependencies measured experimentally and linear expansion l(T) known, the temperature derivative of the refractive indices dn/dT are found to be negative in the ranges above and below the temperature T-i = 130 K.