DISORDER-INDUCED AMORPHIZATION

Many crystalline materials undergo a crystalline-to-amorphous (c-a) ph ase transition when subjected to energetic particle irradiation at low temperatures. By focusing on the mean-square static atomic displaceme nt as a generic measure of chemical and topological disorder, we are l ed quite naturally to a generalized version of the Lindemann melting c riterion as a conceptual framework for a unified thermodynamic approac h to solid-state amorphizing transformations. Tn its simplest form, th e generalized Lindemann criterion assumes that the sum of the static a nd dynamic mean-square atomic displacements is constant along the poly morphous melting curve, so that c-a transformations can be understood simply as melting of critically-disordered crystals at temperatures be low the glass transition temperature where the supercooled liquid can persist indefinitely in a configurationally-frozen state. Evidence in support of the generalized Lindemann melting criterion for amorphizati on is provided by a large variety of experimental observations and by molecular dynamics simulations of heat-induced melting and defect-indu ced amorphization of intermetallic compounds. (C) 1997 Elsevier Scienc e B.V.