Structural disorder and the effects of aging in a phosphate glass: Results from two-dimensional 31P PASS NMR spectroscopy

The nature of the short-range structural disorder and its dependence on the fictive temperature are investigated in a phosphate glass of composition 60ZnO center dot 40P(2)O(5) using P-31 two-dimensional phase adjusted spinning sidebands nuclear magnetic resonance (2D PASS NMR) spectroscopy. The 2D PASS experiment is shown to be a robust method for determining the correlations between the P-31 isotropic shift and chemical shift tensor parameters and their distributions in this glass that allows for a remarkably detailed quantification of structural disorder. The spectra in the isotropic dimension indicate a Q-species disproportionation reaction in this glass of the type 2Q(1)=Q(2)+Q(0) that is driven to the right hand side with increasing fictive temperature. Such a reaction can be a source of configurational entropy as well as a mechanism of Q-species exchange associated with viscous flow in the supercooled liquid. In the anisotropic dimension, the P-31 chemical shift anisotropy (CSA) parameters and their distributions are quantified for the constituent Q-species and are found to be sensitive to the thermal history of the glass. Specifically, the span and the asymmetry parameter of the P-31 chemical shift tensor decrease with lowering of the fictive temperature implying a concomitant increase in the P site symmetry resulting from the structural relaxation of the network. (C) 2012 Elsevier B.V. All rights reserved.