Medium range order studied in selenide glasses by 77Se NMR

Some resolved solid state Se-77 NMR spectra are presented in the AsxSe1-x and GexSe1-x glass families at ambient temperature. Three line positions are observed in the arsenic selenium network assigned to Se-Se-Se, As-Se-Se and As-Se-As selenium neighborhood, whereas only two types of line are exhibited in germanium-selenium glasses assigned to Se-Se-Se and Ge-Se-Ge selenium atom. The relative intensity measurements of these lines are carried out thanks to the reconstruction of the spectra. Then it appears that a scenario involving a selenium clustering process has to be assumed to describe the GexSe1-x medium range order. On the other hand, a structural model based on AsSe3 pyramids homogeneously distributed in the Se network is in better agreement with the NMR results obtained in AsxSe1-x glasses. (C) 2003 Elsevier B.V. All rights reserved.