A new ferroelectric compound: (CH3NH3)5Bi2Br11

The crystals of (CH3NH3)5Bi2Br11 have been found to undergo a ferroparaelectric phase transition of the second-order type at 312.1 K. εc,max reaches 5.5 × 103 at Tc and spontaneous polarization 7 × 10−3 Cm−2 at 285 K. The X-ray diffraction study shows that the crystals belong to the orthorhombic symmetry and consist of methylammonium cations and Bi2Br11−5 anions formed by two BiBr6 octahedra linked via one bromine bridge.