No abstract

The atomic motion of Ag+ ions in superionic and liquid Ag2Se and Ag2Te has been investigated by coherent quasi-elastic neutron scattering. The presence of a Q-dependent broadening of the quasielastic peak indicates that the Ag+ ion is mobile in the superionic phase of both materials. This motion takes place within a body-centred cubic sub-lattice of Se2- or Te2- ions respectively. Two Lorentzian components were required in order to fit the quasi-elastic broadening: a narrow peak that is attributed to the diffusion of the cations, and a much broader and less intense component that may be due to a localized motion of these ions. An asymmetry in the quasi-elastic peak indicates the presence of a low-energy excitation as reported for other superionic materials. The widths of the narrower Lorentzian showed the characteristic de Gennes narrowing at Q values close to the maximum in SAgAg(Q). A comparison of the widths of the quasi-elastic peak for the two liquids indicates a similar Ag+ diffusion coefficient but a difference in the mechanism of diffusion. The results for liquid Ag2Te indicate a jump-diffusion mechanism in comparison to those for Ag2Se that follow Fick's law.

The partial structure factors and pair distribution functions for liquid Ag2Te have been measured using the method of neutron diffraction and isotopic substitution. The partial structure factors are consistent with a melt in which the predominant interactions are ionic in nature and in which the small Ag+ ions are highly disordered and move rapidly through a more ordered Te2- sub-structure. A detailed comparison has been made between the structure of this liquid and that of liquid Ag2Se. It is observed that the main structural features of the two liquids are similar but a significant difference is observed in SAgAg(Q). The differences in the electronic properties of the two liquids are discussed in light of these results.

The partial structure factors of liquid thallium selenide, TlSe, have been determined using a combination of two neutron diffraction measurements using isotopic substitution and one x-ray diffraction measurement. We show that the statistical accuracy obtained using this method is considerably higher than that achievable using neutron diffraction and isotopic substitution alone. The results unambiguously show the formation of Se polyanionic species in the liquid.

2001) A determination of the structure of liquid Ga 2 Te 3 using combined Xray diffraction and neutron diffraction with isotopic substitution, Molecular Physics, 99:10, 767-772,The partial structure factors of liquid Ga2Te3 have been determined using a combination of neutron diffraction with isotopic substitution (NDIS) and anomalous X-ray diffraction around the Te K edge. The inclusion of X-ray diffraction data significantly improves the statistical accuracy of the partial structure factors obtained compared with those obtained by the NDIS method alone. The results show that the liquid is hetero-coordinated in a way similar to that of typical two-component glasses or ionic liquids. There is no evidence, within the accuracy of this experiment, for substantial numbers of homopolar bonds as suggested by recent ab initio molecular dynamics simulations. The bond distances and coordination numbers show strong similarities to the tetrahedrally bonded defective zinc blende structure of the crystalline solid before melting.