MODELING THE METAMICTIZATION OF ION-BOMBARDED CERAMICS

The Segregation Charge Transfer (SCT) model, applied with success to m any binary alloys, is extended and adapted to interpret the nucleation either of crystalline or amorphous phases in binary ceramics undergoi ng ion bombardment under conditions that form dense collision cascades . A non-equilibrium compositional profile evolves at the cascade-matri x 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 a toms. At the interface between the cascade and the matrix, a pair of i onized atoms is formed. The sum of the volumes of ionized atoms enteri ng the CTR and of neutral atoms which exceed the ratio needed by the r eaction, is compared to the volume occupied in the starting compound u nit cell by a prototypical stoichiometric unit. In principle, the loca l deformation, related to the local volume changes, can be high enough to structurally destabilize the crystal. The absolute value of the re lative volume variation due to a CTR has been evaluated. (C) 1998 Else vier Science B.V. All rights reserved.