Kinetics of decomposition in ionic solids: III. Time evolution of phonons during spinodal decomposition in AgCl-NaCl

Real-time inelastic neutron scattering has been used to study the kinetics of the demixing process in AgCl-NaCl mixed single crystals. The variation of transverse acoustic phonon spectra provides the most direct information about the microscopic non-equilibrium behaviour. It is shown that a well defined splitting of phonon peaks corresponding to the formation of the product phases takes place on a timescale of seconds. Along with the observation of satellite reflections these findings clearly demonstrate that the phase separation is governed by the mechanism of spinodal decomposition in this ionic system. During the entire process the lattice parameter keeps almost unchanged, thus leading to a metastable state characterized by large coherency strains.