Direct evidence for intrinsically broken 8 -Ncoordination rule in melt-quenched glasses by a novel method

Abstract

The sign of the electric field gradient at $^{129}\mathrm{I}$ atoms formed from nuclear decay of $^{129m}\mathrm{Te}$ parent atoms undergoes a change from positive to negative when the parent-atom coordination changes from 2 to 3. This provides a sensitive way to discriminate twofold from threefold Te sites in glasses by use of $^{129}\mathrm{I}$ M\"ossbauer emission spectroscopy. Evidence for some threefold Te sites in ${\mathrm{As}}_{x}{\mathrm{Te}}_{1\ensuremath{-}x}$ glasses is presented indicating the first clear breakdown of 8 -$N$ coordination rule intrinsic to a glass network.