Structure of GeSsub2glass: Spectroscopic evidence for broken chemical order

Homogeneous melt-quenched (Ge0.99{Sn}0.01)ₓS _1-x glasses in the glass-forming range 0 (1/3). This provides evidence for chemically correlated regions in GeS₂ glass which consist of two types of clusters---an A molecular cluster whose internal morphology is layerlike as in c-GeS₂ and a B molecular cluster whose building block consists of ethanelike Ge₂(S1/2{)}₆$ units. The 340-${cm}^{{{-}}1}$ Raman band observed in ${GeS}₂$ glass is identified as having scattering contributions from both ordered bonds: ${A}₁$ from the symmetric stretch of Ge(${S}1/2)₄ units; and disordered bonds: A1g mode from Ge₂(S1/2{)}₆$ units; in the Ge-rich glasses (x>(1/3)), a third type of molecular cluster, C, is populated. The internal morphology of the C cluster resembles that of c-GeS and it consists of double layers. The 250-cm^-1 Raman band, whose strength is correlated to the M\"ossbauer C sites, is identified as a double-layer breathing mode. The molecular structures of GeS₂ and GeSe₂ glasses are compared and contrasted.