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

Under heavy-ion bombardment, predominantly covalent $A^N{B}^{8-N}$ crystals become amorphous while predominantly ionic crystals do not. The critical ionicity (Phillips scale) which separates these two classes in $f_i^{\mathrm{ac}}=0.41\mathrm{}$, so that AIN ($f_i=0.45\mathrm{}$) 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 [$f_i\left(\mathrm{InN}\right)=0.58\mathrm{}$].