LOCAL-STRUCTURE AND CONNECTIVITY IN LITHIUM PHOSPHATE-GLASSES - A SOLID-STATE P-31 MAS NMR AND 2D EXCHANGE INVESTIGATION

High resolution solid-state P-31 magic angle spinning (MAS) nuclear ma gnetic resonance (NMR) spectroscopy has been used to investigate the l ocal structure and connectivity for three xLi(2)O .(1-x)P2O5 glasses. The principal components of the P-31 chemical shift anisotropy (CSA) t ensors for the different phosphate tetrahedron sites (Q(n)) and the re lative populations of each Q(n) species were determined from simulatio n of the MAS spectra. The medium range structure and connectivity betw een 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 rei ntroduction of the through space (31)p-(31)p dipolar-dipolar interacti on even in the presence of fast MAS. For these binary phosphate glasse s the connectivity and medium range structure for different Q(n) speci es is described well by a statistical distribution, and is consistent with a model of random depolymerization. (C) 1998 Elsevier Science B.V .