Dilatometric Study of Critical Behavior in KH₂PO₄

Abstract

Dilatometric measurements have been made on KH₂PO₄ along the ferroelectric c-axis over the temperature range from 90 K to 240 K. Discrepancy between the phenomenological theory and the experimental result is found in the temperature dependence of the spontaneous strain near the Curie temperature, T_c. It is shown that the anomalous part of the thermal expansion coefficient above T_c changes logarithmically on T−T_c in the temperature range 0.15 K\lesssimT−T_c\lesssim15 K.