Symmetry of the lattice vibrations in perovskite-type layer structures

Abstract

Starting with the 'family tree' which shows the group-subgroup relations between the various structural phases of perovskite-type layer materials with organic ions, the symmetry types of the lattice vibrations and, for some selected cases, the symmetry coordinates are derived by standard group theoretical methods. Special emphasis is given to the possibility of soft or condensating modes in the phase transitions involved and to the applicability of the Landau theory of phase transitions.