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⇌Li4P2O7+Li2W2O7. The proportions of the various structural groupings are determine d 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 O 1s core-levels are determined. The O 1s 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.