Single and collective particle dynamics in liquid Rb-80(RbBr)(20)

International audienceThe temperature (T) dependence of the single and the collective particle dynamics of a melt containing 80 at% Rb and 20 at% RbBr was investigated using neutron inelastic scattering. Compared to pure liquid Rb, the dispersions obtained from the maxima of the longitudinal current correlation function clearly reflect the change of the atomic interaction from a metallic to a dominantly ionic regime. The T dependence of the atomic dynamics in Rb80(RbBr)20 is characterized by a broadening of the spectra resulting in a shift to higher energies in the dispersion and in the spectrum of the velocity auto-correlation function, which was determined here for a mixture of a liquid metal with a molten salt for the first time

Inelastic neutron and Raman scattering of poly(methyl methacrylate): Nanostructure of polymer glasses

Low-energy excitations were investigated in amorphous poly(methyl methacrylate) by means of both neutron and Raman scatterings, in a wide temperature interval. The frequency dependence of the light-vibration coupling coefficient was deduced, especially at low temperature where the quasi-elastic contribution is not significant; it was not found to be linear. The vibrational density-of-states anomaly is interpreted in the frame of a non-continuous glassy nanostructure, which is characterized by a log-normal size distribution of domains

Semi-Conductor to Metal Transition in Liquid Selenium at High Pressure and High Temperature

Near its critical point (385 bars, 1615 °C), semiconducting liquid Se gives way to a metallic state (SC-M transition). In this paper we report for the first time XANES and EXAFS measurements on liquid Se in the temperature and pressure range up to 600 bars and 1500°C, in the temperature interval where the electrical conductivity shows the SC-M transition. Both the XANES spectra and the Fourier transforms of the EXAFS modulations present significant modifications. The results obtained with an anharmonic analysis (cumulant expansion method) show that the helical chains get shorter as temperature raises, but, even at the highest temperatures, they are not shorter than 5 atoms. The reconstruction of the distances distribution function for the first shell shows that, in the metallic region, the mean distance value decreases down to about 2.23 Å and the distributions show an important asymmetry towards lower values of R