Structural stability of ion bombarded non-metallic systems

The Segregation Charge Transfer (SCT) model, already applied to binary meta llic alloys, is adapted to interpret the nucleation either of crystalline, or of vitreous phases in binary non-metallic compounds ion bombarded under conditions favourable to the formation of dense collision cascades. At the cascade-matrix interface a non-equilibrium electronic density profile devel ops; it is re-equilibrated by charge transfer reactions (CTRs), each involv ing a couple of dissimilar atoms, which are ionized. The sum of the volumes of such ionized atoms and of neutral atoms which exceed the stoichiometry ratio needed by the reaction, is compared to the volume occupied in the sta rting compound unit cell by a prototypical stoichiometric unit. The local d eformation associated to the local volume changes can be high enough to str ucturally destabilize the surrounding crystal. The absolute value of the re lative volume variation due to a CTR has been evaluated for 26 systems. A t hreshold value of such a structure stability parameter, allowing us to sepa rate crystalline from amorphized compounds has been found. (C) 1999 Elsevie r Science B.V. All rights reserved.