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 Se-77 Car-Purcell-Meiboom-Gill (CPMG) spikelet nuclear magnetic resonance (NMR) spectroscopy. When taken together, these spectroscopic results allow for self-consistent assignment of average Se-77 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 Se-77 NMR line shapes of Se-excess glasses on the basis of the revised structural assignments of Se-77 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. (C) 2011 Elsevier B.V. All rights reserved.