Microscopic theory of covalent-ionic transition of amorphizability of nonmetallic solids

Abstract

Under heavy-ion bombardment, predominantly covalent ${A}^{N}{B}^{8\ensuremath{-}N}$ crystals become amorphous while predominantly ionic crystals do not. The critical ionicity (Phillips scale) which separates these two classes in ${f}_{i}^{\mathrm{ac}}=0.41$, so that AIN (${f}_{i}=0.45$) is grouped with II-VI and I-VII compounds as nonamorphizable. Several thermomechanical defect models are discussed and are found to give values of ${f}_{i}^{\mathrm{ac}}$ which are too high. I conclude that nonamorphizability is the result of recombination-enhanced defect annealing. If this is the case, then InN is predicted to be amorphizable, even though its Phillips ionicity is high [${f}_{i}(\mathrm{InN})=0.58$].