RAMAN AND X-RAY PHOTOELECTRON SPECTROSCOPIC STUDIES OF LITHIUM PHOSPHOTUNGSTATE GLASSES

Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) are used to investigate the 0.5 Li2O:0.5[(1-X)P2O5:XWO3] glassy system. Raman spectroscopy shows that besides the expected metaphosphate tetrahedra and tungstate tetrahedra, pyrophosphate tetrahedra and tungstate octahedra are also present. A reaction in the glass melt is proposed: 2 LiPO3+2 Li2WO4 reversible Li4P2O7+Li2W2O7. The proportions of the various structural groupings are determined from the associated Raman peak areas. Structural groupings characteristic of the highly conducting Li4P2O7 and Li2W2O7 phases are the most abundant at around x = 0.6. This offers a plausible explanation for the conductivity maximum previously observed near this composition. From the XPS spectra, binding energies of the Li 1s, P 2p, W 4f and 0 Is core-levels are determined. The 0 Is spectrum is found to consist of two peaks which are attributed to the P=O, P-O-P, P-O, W-O-W and W-O oxygen species. The proportion of the P-O-P species decreases as x increases. Good agreement is found between the XPS data and the Raman data.