Ferroelectric Phase Transition in Hexagonal Antiferromagnet RbFeBr₃ with Linear Chains of Face-Sharing Octahedra (FeBr₆)^4-

Abstract

A hexagonal antiferromagnet RbFeBr₃ 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. RbFeBr₃ is a new type of ferroelectric crystal, the crystal structure of which is characterized by linear chains of face-sharing octahedra (FeBr₆)^4- along the c-axis (h-h-h packing). The ferroelectricity in RbFeBr₃ 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 P6₃cm below T_c.