Ferroelastic phase transition in (CH3NH3)3Bi2Br9single crystal

Abstract (CH3NH3)3Bi2Br9 (MABB) is known to undergo successive phase transitions starting from the high temperature P3m1 phase (phase I). We investigated domain structures and pyroelectricity in MABB. Ferroelastic domains could be observed with a polarizing microscope in all low temperature phases II, III and IV. The transition from the phase I to the phase II was group-theoretically interpreted, and it is conjectured that the transition is induced either by the Eg representation at the γ-point or by a zone-boundary representation.