Coordination-number-induced morphological structural transition in a network glass

Mössbauer electric field gradients, Raman vibrational modes, and crystallization temperatures exhibit threshold behavior near the composition x=0.20 in binary ${\mathrm{Si}}_{\mathrm{x}}$ ${\mathrm{Te}}_{1\mathrm{-}\mathrm{x}}$ glasses. This threshold is evidence of a morphological structural change that may be driven by network connectivity or average coordination number. At x≤0.20, the network largely consists of Si-cross-linked ${\mathrm{Te}}_{\mathrm{n}}$ chain segments. At x≥0.20, ${\mathrm{Te}}_{\mathrm{n}}$ chains reconstruct with tetrahedral Si(${\mathrm{Te}}_{1/2}$ ${)}_4$ units and nucleate a defect-ridden ${\mathrm{Si}}_2$ ${\mathrm{Te}}_3$-like layered molecular fragment. These fragments represent the elastically rigid domains that percolate above the threshold.