Ferroelectric Phase Transition in Hexagonal Antiferromagnet RbFeBr₃with Linear Chains of Face-Sharing Octahedra (FeBr₆)^4-

Abstract

A hexagonal antiferromagnet RbFeBr 3 was found to undergo successive structural phase transitions at T I (=109.0 K) and T c (=34.4 K) and to be ferroelectric along the hexagonal c -axis below T c . RbFeBr 3 is a new type of ferroelectric crystal, the crystal structure of which is characterized by linear chains of face-sharing octahedra (FeBr 6 ) 4- along the c -axis (h-h-h packing). The ferroelectricity in RbFeBr 3 is attributed to possible shifts of two-thirds of the chains antiparallel to the remaining one-third along the c -axis, which are possible due to the crystal symmetry of P 6 3 c m below T c .