Time-resolved phonons as a microscopic probe for demixing processes

Time-resolved inelastic neutron scattering from acoustic phonons has been used to characterise the mechanism of demixing in ionic crystals of the silver alkali halide type. Stroboscopic techniques allow to study the time-evolution of phonon spectra during the phase separation in AgBr-NaBr and AgCl-NaCl single crystals on a time scale of seconds. These data provide the most direct information about changes of interatomic interactions. Characteristic differences are observed for ageing temperatures above and below the spinodal temperature which allow to distinguish between different mechanisms based on nucleation on the one hand and concentration fluctuations on the other. (C) 2004 Elsevier B.V. All rights reserved.