Ferroelectricity in NH₄LiSO₄

Abstract

It has been found that in NH 4 LiSO 4 another transition point 186.5°C exists in addition to the already known one 10°C and this substance is ferroelectric between these two transition points. Anomalies of dielectric constant at the transition points are very small as compared with those of proper ferroelectrics. The Curie-Weiss law holds within a narrow temperature range in the phase above the upper transition, where the Curie constant has a very small value of 5.6 K. Moreover the spontaneous polarization shows a curious increase with lowering temperature. Thus NH 4 LiSO 4 can be said to be one of improper ferroelectrics.