Ferroelectricity in CH₃NH₃AlBr₄

Abstract

The dielectric properties of single-crystal CH 3 NH 3 AlBr 4 have been studied. The crystal belongs to the tetragonal system at room temperature. It shows ferroelectricity along the a -direction below the Curie temperature T c =76.6 K. The dielectric constant along the a -direction obeys a Curie Weiss law above T c with the Curie constant being 3.7×10 2 K. The spontaneous polarization measured by means of 50 Hz hysteresis loop at 64 K is 6.6×10 -3 C/m 2 . Besides the ferroelectric transition, a first order structural phase transition is found at about 250 K.