Microscopic structure of the glassy ionic conductor x•LiF+(1-x)•LiPO3 from NMR data

The structure of phosphate glasses of the nominal composition x . LiF + (1 - x) . LiPO3 has been studied for 0 < x < 0.35, using H-1, Li-7, F-19, P-31 NMR. By combining data from different nuclei and various solid state NMR techniques structural information on the molecular scale is obtained. The measurements confirm that the structural units of the glass are polyphosphate chains, and allow determination of their average length. The increase of LiF concentration, x, from 0 to 0.35 leads to a shortening of the chains from 29 to 4 phosphate units by use of Li and F to form terminal groups. Fluorine is partitioned between two structural units: fluorophosphate terminal groups and Li+F- fragments, in a ratio of about 1:1 at low x and decreasing to 1:4 at high x. Substantial loss of fluorine during glass preparation is observed and measured. (C) 1998 Elsevier Science B.V. All rights reserved.