A combined 77Se NMR and Raman spectroscopic study of the structure of GexSe1-x glasses: Towards a self consistent structural model

The short-range structures of stoichiometric and Se-deficient binary GexSe100 −x glasses with 42 ≥ x ≥ 33.33 have been investigated using a combination of Raman and 77Se Car–Purcell–Meiboom–Gill (CPMG) spikelet nuclear magnetic resonance (NMR) spectroscopy. When taken together, these spectroscopic results allow for self-consistent assignment of average 77Se NMR isotropic chemical shifts to Se atoms in various coordination environments in GexSe100 −x glasses. Analysis of the compositional variation of the relative concentrations of these Se environments indicates considerable violation of chemical order in the nearest-neighbor coordination environments of the constituent atoms in the stoichiometric Ge33.33Se66.67 glass. On the other hand, the presence of a random distribution of Ge―Ge bonds can be inferred in the Se-deficient glasses. Simulations of the previously published 77Se NMR line shapes of Se-excess glasses on the basis of the revised structural assignments of 77Se NMR chemical shifts obtained in this study conclusively indicate that the structure of these glasses is intermediate between a randomly connected and a fully clustered network of GeSe4 tetrahedra and Se chains.