Kinetics of decomposition in ionic solids: IV. Transition between nucleation and spinodal decomposition observed by time-resolved phonon spectroscopy

Real-time inelastic neutron scattering has been used to study the kinetics of the demixing process in AgBr-NaBr mixed single crystals. The variation of transverse acoustic phonon spectra provides most direct information about the microscopic non-equilibrium behaviour. The phase separation is monitored by a well defined splitting of phonon peaks that reflects the different dynamical behaviours of the constituents. As a function of temperature, time evolution of the phonon spectra changes drastically, thus proving unambiguously that the demixing process is dominated by nucleation in the high-temperature regime and by concentration fluctuations at low temperatures.