Local structure and connectivity in lithium phosphate glasses: a solid-state 31P MAS NMR and 2D exchange investigation

Abstract

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 xLi 2O·(1 - x)P 2O 5 glasses. The principal components of the 31P chemical shift anisotropy (CSA) tensors for the different phosphate tetrahedron sites (Q n ) and the relative populations of each Q n species were determined from simulation of the MAS spectra. The medium range structure and connectivity between similar or different Q n 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 Q n species is described well by a statistical distribution, and is consistent with a model of random depolymerization.