GLASS-FORMING TENDENCY, PERCOLATION OF RIGIDITY, AND ONEFOLD-COORDINATED ATOMS IN COVALENT NETWORKS

A three-dimensional covalent network of N atoms possessing a fraction (n(r)/N) of r-fold-coordinated atoms will, in general, display percolation of rigidity at an average coordination number (r) = 2.4-0.4(n1/N), where n1/N represents the fraction of onefold-coordinated atoms. As an example, we show how these ideas can elucidate the glass-forming region in the Ge-S-I ternary system.