Structural Transitions in Superionic Conductors

The $\alpha \rightleftarrows \beta$ phase transition in AgI is studied with use of the new molecular-dynamics technique which allows for a dynamical variation of the shape and size of the cell. In the present model, upon heating of $\beta$-AgI, the iodine ions undergo a hep → bee transformation and silver ions become mobile, whereas the reverse transformation is observed on cooling of $\alpha$-AgI. The calculated $\alpha \rightleftarrows \beta$ transition temperature and structural and dynamical properties are in good agreement with experiments.