Dielectric behaviour of the new ferroelectric (CH3NH3)5Bi2Br11 in the microwave region

Abstract Low frequency dielectric measurements reveal two phase transitions in (CH3NH3)5Bi2Br11: at 311.5 K and 80 K. In the very vicinity of the ferroelectric phase transition at Tc = 311.5 K a nearly perfect Debye relaxation in the MHz region, with a critical slowing down of the relaxation frequency fe= ½πτe has been found. Well-marked deviations from this behavior in the GHz range can be interpreted as the influence of another relaxational contribution to the permittivity.