Symmetry and lattice dynamics of oxides with perovskite-like structures

Based on a topological definition the possible space groups for a perovskite-like structure are derived for small unit cells. The irreducible representations are calculated from them for interpretation of the phonon spectra. To compare the character of the bonds in some oxides, Raman spectra have been taken and interpreted on the basis of a simple lattice-dynamical model. It was found that covalent interaction occurs in Na_xWO₃ and XIO₃ (X = NH₄, K, Rb, Cs) whereas titanates and niobates are mainly ionic. A model for classification of perovskite-like compounds is discussed.