Structural analysis of Cu-As-Te glasses: Results from Raman and 65Cu NMR spectroscopy

The structure of Cu-As-Te glasses is investigated using a combination of Cu-65 Nuclear Magnetic Resonance (NMR) and Raman spectroscopy. A comparison of Cu-65 NMR spectra from a series of glasses and two reference crystalline phases CuInTe2 and CuGaTe2 reveals that Cu in all glasses invariably adopts a tetrahedral coordination with Te. This assignment is consistent with the presence of a sharp CuTe4 tetrahedral mode in all Cu-As-Te Raman spectra. The Raman spectra of Cu-As-Te and Ge-As-Te glasses of identical compositions suggest that the short range order of As and Te is the same in both systems. Te-125 NMR results corroborate this hypothesis. However, the breach in chemical order commonly observed in Ge-As-Te does not appear to occur in Cu-As-Te. The variation in glass transition temperature with composition shows identical trends for Cu-As-Te and Ge-As-Te glasses, however, the density trends for these two systems show dramatic differences. Such trends are partly controlled by the difference in chemical order in these telluride glasses. (C) 2015 Elsevier B.V. All rights reserved.