X-ray scattering measurements of an expanded liquid Se80Te20 mixture in the temperature range between 300 and 1000C and at pressures of 10, 200 and 1600bar were carried out. The reverse Monte Carlo simulation and Voronoi–Delaunay void analyses were applied to clarify the relationship between the voids and chain geometries in the intermediate scale near the semiconductor to metal transition at 800C under 200bar accompanied by a shrinkage of the molar volume. The structure of the liquid mixture could be envisaged in terms of a packing of covalently bonded chains and interstitial voids. The thermal expansion led to a decrease in the number of chains around a chain and was compensated for by empty spaces (voids). The packing density of helical chains decreased and so voids supported by chains increased with rising temperature. At high temperature the shortening of chains and frequent transfer of lone pair electrons on Se (or Te) atoms cause modification of the helical chain to ring and zigzag chain conformations. The stacking of zigzag chains, joined to layers above 800C, led to the formation of metallic domains separated by voids. The shrinkage of molar volume near the semiconductor to metal transition arose through the progressive filling of the voids around chains with (Se, Te)5, 6, 7, 8 rings.

Packing Structure of Chains and Rings in an Expanded Liquid Se80Te20 Mixture Near the Semiconductor to Metal Transition. K.Maruyama, H.Endo, H.Hoshino, Y.Kajihara, M.Nakada, S.Sato: Journal of Physics - Condensed Matter, 2010, 22[45], 455103