Dielectric Evidence for Low Temperature Phase Transitions in Ferroelectric Rb₂CoCl₄and Rb₂CoBr₄Crystals

Abstract

Single crystals of Rb 2 CoCl 4 and Rb 2 CoBr 4 were grown from melt, and dielectric constants were measured along the three crystallographic axes down to liquid helium temperature. Below the ferroelectric Curie temperature T c ( T c =192 K for Rb 2 CoCl 4 and 180 K for Rb 2 CoBr 4 ) there are one phase transition at 66 K in Rb 2 CoCl 4 and two transitions at 95 K and 65 K in Rb 2 CoBr 4 . Dielectric anomalies at these low temperature transitions in Rb 2 CoX 4 (X: Cl, Br) are quite similar to those in the corresponding Rb 2 ZnX 4 crystals.