Rigidity Percolation and Molecular Clustering in Network Glasses

Abstract

${}_{}{}^{129}{}_{}{}^{}\mathrm{I}$ Mössbauer spectra of $g-{\mathrm{Ge}}_x{\mathrm{Se}}_{1-x}$ alloys display a local maximum in the site-intensity ratio $\frac{I_B}{I_A}\mathrm{}\left(x\right)\mathrm{}$ at the critical composition $x=x_c=0.23\mathrm{}\pm 0.02$. This observation is consistent with the realization of mechanical critical behavior in a covalent network glass recently predicted by Phillips and Thorpe. We identify $x_c$ with the onset of percolation of a specific molecular fragment based on the layered form of $c-\mathrm{Ge}{\mathrm{Se}}_2$.