Re-entrant Peierls distortion in IV-VI compounds

Complete text of publication follows. At room temperature, the local structure of crystalline group V elements and their group IV-VI isoelectronic compounds is governed by a Peierls distortion of the cubic NaCl structure [1]. The morphology of the distortion is determined by the filling ratio of the p-band. At higher temperature, the crystalline structure shows, at least approximately, the cubic symmetry. Neutron diffraction experiments in the liquid state (λ = 0.7 A) demonstrate that the Peierls distortion is recovered. This behaviour is observed and discussed for a series of tin and germanium chalcogenides: SnS, SnSe, GeSe and GeTe and their temperature evolution is discussed. The heaviest IV-VI compounds does not show this behaviour. It is shown that the hardness of the repulsive potential is a key parameter in this mechanism. A comparison is made with the parent alloys AsxSb1-x [2]. Finally the composition dependence of the local order for Gex-Te1-x alloys is discussed. (author)