The structure and dynamics of liquid semiconductors and superionic conductors by neutron scattering

The structure and dynamics of the binary liquid semiconductors and superionic conductors Ag_2Se, Ag_2Te, Cu_2Se and Mg_3Bi_2 have been considered with respect to their electronic properties. The structure of Ag_2Se in the superionic phase has been determined by neutron diffraction with isotopic substitution at 327 deg. C and 800 deg. C. The partial structure factors and pair distribution functions have been compared to those for the liquid in order to determine the effect of temperature on the structure. Little difference was observed over a temperature range of 327-1000 deg. C. The structures of liquid Ag_2Te and Cu_2Se have been determined to the partial structure factor level by neutron diffraction with isotopic substitution and compared to Ag_2Se. In general the structures of these liquids are similar and all show features characteristic of ionic melts. The cation-cation structure factor for liquid Ag_2Se has a first peak at #approx# 1.8 A"-"1. This peak is much weaker in the results for Ag_2Te and does not exist in those for liquid Cu_2Se. There is evidence of such a peak at the total structure factor level for liquid Mg_3Bi_2. The dynamics in Ag_2Se, Ag_2Te and Mg_3Bi_2 have been determined by quasielastic neutron scattering in the superionic and liquid phases. There is significant quasielastic broadening in all cases. However the Q-dependence of the widths of a single Lorentzian fit indicate a continuous diffusion in Ag_2Se and a jump mechanism in Ag_2Te. This observation is consistent with the differences observed in the structure of the liquids. The results for Mg_3Bi_2 confirm that the Mg"2"+ ion is mobile and show a low energy excitation prior to the superionic phase transition. The observation of differences in the cation distribution and diffusion in these liquids is consistent with the suggestion that the unusual electronic properties of Ag_2Se and Mg_3Bi_2 may be linked to the ionic mobility. (author)Available from British Library Document Supply Centre-DSC:DXN032984 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo