Evidence for Ferroelectricity in Iv-vi Compounds

Because the usual methods for establishing ferroelectricity in crystals are not possible for crystals with high conductivities, other ways must be introduced based on other ferroelectric prop&rties. ~nalysisof the crystal structure can provide a model showing the possibility of reversible polarisation, but more convincing evidence can come from the study of the dynamics of the crystal. Neutron inelastic coherent scattering yields the frequencies of the normal modes of the crystal, and the temperature dependence of certain modes can point to ferroelectricity or antiferroelectricity. Examples of both these phenomena are presented for SnTe, suggesting moreover that the solid solutions of SnTe with GeTe form a wide ferroelectric range.