Kinetics of decomposition in ionic solids: neutron scattering study of the system AgBr-NaBr

The kinetics of decomposition in the quasibinary ionic system AgBr-NaBr has been studied by time-resolved neutron diffract ion and small-angle scattering. The temperature regimes for nucleation and for spinodal decomposition are dearly distinguished The coherent critical point is estimated as 458 +/- 5 K which is about 100 K below the maximum of the chemical binodal. Even at low temperatures the chemical demixing is completed within some 100 s resulting in a metastable state which is characterized by coherency strains and internal stresses of the order of 0.3 GPa. The mechanical relaxation of the lattice takes place on a much longer timescale after the correlation length of the decomposition pattern is increased to some critical value larger than 40 nm.