The cubic perovskite substance CH3NH3PbCl3 exhibits two low temperatur
es 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 invol
ves mainly the rotational and orientational motions of the organic cat
ion, whereas the antiferroelectric transition at 172K is connected wit
h a complex mechanism involving the freezing of the cation motions cou
pled with the distortion of the PbCl6 octahedra. This phase sequence h
as been also analysed in terms of pseudo-spin theory.