A combined 77Se NMR and Raman spectroscopic study of the structure of GexSe1-x glasses: Towards a self consistent structural model |
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Authors: | Trenton G Edwards Sabyasachi Sen Erica L Gjersing |
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Institution: | Department of Chemical Engineering and Materials Science, University of California Davis, Davis, CA 95616, USA |
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Abstract: | 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. |
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