Modeling the metamictization of ion bombarded ceramics

Abstract

The Segregation Charge Transfer (SCT) model, applied with success to many binary alloys, is extended and adapted to interpret the nucleation either of crystalline or amorphous phases in binary ceramics undergoing ion bombardment under conditions that form dense collision cascades. A non-equilibrium compositional profile evolves at the cascade-matrix interface and is associated with a local non-equilibrium electronic density profile. Relaxation to (meta) stable equilibrium is simulated by a Charge Transfer Reaction (CTR) involving coupling of dissimilar atoms. At the interface between the cascade and the matrix, a pair of ionized atoms is formed. The sum of the volumes of ionized atoms entering the CTR and of neutral atoms which exceed the ratio needed by the reaction, is compared to the volume occupied in the starting compound unit cell by a prototypical stoichiometric unit. In principle, the local deformation, related to the local volume changes, can be high enough to structurally destabilize the crystal. The absolute value of the relative volume variation due to a CTR has been evaluated.