Vibrational thresholds near critical average coordination in alloy network glasses.

Experimental evidence for vibrational thresholds in network glasses recently predicted theoretically is discussed. A number of thresholds are observed, some of which are ascribed to phase separation and some of which may arise from intrinsic network mechanical properties. The glasses are binary and ternary chalcogenide alloys of Ge and Sn with S and Se, and the experiments are either acoustical or optical (Raman scattering), with variable composition and external pressure.