OPTICAL AND DILATOMETRIC MANIFESTATIONS OF PHASE-TRANSITIONS IN K2SEO4 CRYSTAL

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