Phase Transitions in the Organic-Inorganic Perovskites

Ian Swainson NRC, Canada

The organic-inorganic perovskites are perovskite structures with typically amine-based cations in place of simple cations in the structure. The resulting phase transitions are combinations of effects due to both the inorganic framework, and orientational ordering and hydrogen bonding from the organic cations. On cooling, orientational ordering and tilting coexist, and typically there are superlattices of tilt systems generated. However, under pressure, the evidence to hand says that the samples amorphize after undergoing 1-2 transitions that do not involve cation ordering, so that coupling to volume appears to dominate. The wavevectors of the "famous" modulated phases of propylammonium tetrahalometallates are shown to be determined by the distribution of certain classes of modes, whose distribution in the Brillouin Zone is determined by the connectivity of the inorganic component. I will also discuss evidence of interaction between hydrogen bonding and lone pair distortions in Sn2+ based perovskites, and how this may relate to disorder effects in the Ge2+ salts.

Back to Seminar Home Page

Last modified 07-August-2006 by website owner: NCNR (attn: )