Ferroelectric Phase Transition in (NH₄)₃H(SeO₄)₂

Abstract

Dielectric properties of single crystal (NH 4 ) 3 H(SeO 4 ) 2 were measured below room temperature. Two phase transitions were found at around +2°C and at -92°C. A λ-type peak of the dielectric constant along the c -direction is found at -92°C, and the crystal shows ferroelectricity below the transition. The temperature dependence of the spontaneous polarization was measured by a pyroelectric method. The Curie temperature linearly increases with increasing hydrostatic pressure up to 8.5 kbar with a slope of 2.3 deg kbar -1 .