Universal structural phase transition in network glasses

Raman and Mössbauer spectroscopy provide evidence for a transition from a molecular-cluster network at x=0 to a continuous network at x=0.35 in ${\mathrm{Ge}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Sn}}_{\mathrm{x}}$ ${\mathrm{Se}}_2$ alloy glasses. The nature of this morphological transition can be understood in terms of a reformation of molecular-cluster surfaces in the heterogeneous phase to yield a homogeneous phase. The transition is believed to be a universal property of covalent networks and can be effected in one of several ways. In the present experiments, this transition has been stimulated by alloying, i.e., chemical tuning of cation constraints.