Crystal dynamics and pseudo-spin theory analysis in the perovskite CH3NH3PbCl3

The cubic perovskite substance CH3NH3PbCl3 exhibits two low temperatures phase transitions according , the phase sequence : III (P222(1)) <-- (172K) --> II (P4/mmm) <-- (179K) --> I (Pm3m) The three phases have been caracterized by Raman spectroscoy. The I <-> II transition involves mainly the rotational and orientational motions of the organic cation, whereas the antiferroelectric transition at 172K is connected with a complex mechanism involving the freezing of the cation motions coupled with the distortion of the PbCl6 octahedra. This phase sequence has been also analysed in terms of pseudo-spin theory.