Local Structure and Connectivity in Lithium Phosphate Glasses: A Solid-state ³¹P MAS NMR and 2D Exchange Investigation

High resolution solid-state 31P magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy has been used to investigate the local structure and connectivity for three xLi2O · (1 - x)P2O5 glasses. The principal components of the 31P chemical shift anisotropy (CSA) tensors for the different phosphate tetrahedron sites (Qn) and the relative populations of each Qn species were determined from simulation of the MAS spectra. The medium range structure and connectivity between similar or different Qn units in these lithium phosphate glasses were probed using novel two-dimensional (2D) MAS exchange experiments. Radio-frequency dipolar recoupling (RFDR) techniques allowed the reintroduction of the through space 31P-31P dipolar-dipolar interaction even in the presence of fast MAS. For these binary phosphate glasses the connectivity and medium range structure for different Qn species is described well by a statistical distribution, and is consistent with a model of random depolymerization. © 1998 Elsevier Science B.V.