Molecular dynamics simulation of premelting effect in AgBr

The effect of premelting in silver bromide crystals has been simulated for the first time. It is shown that at the temperature about 150°C lower than the melting point of silver bromide, a considerable increase in the mobility in the cationic sublattice is observed, whereas the (self-)diffusion coefficient of silver ions attains values exceeding 10 −6 cm 2 /s. The assumption about the superionic nature of conductivity in the region of premelting is confirmed by the break of the long-range order in the cationic subsystem, which, in turn, is confirmed by the comparison of the pair cation-cation correlation functions far from and in the vicinity of the melting point. It is established that the premelting effect correlates with the experimentally observed effect of a considerable increase in ionic conductivity in the vicinity of the melting point. It is shown that the premelting effect in AgBr is similar to the diffuse superionic phase transition in anionic conductors of the M F 2 family ( M = Ca, Ba, Sr, and Pb).