Raman and X-ray photoelectron spectroscopic studies of lithium phosphotungstate glasses
Abstract Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) are used to investigate the 0.5 Li 2 O:0.5[(1− x )P 2 O 5 : x WO 3 ] 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 LiPO 3 +2 Li 2 WO 4 ⇌Li 4 P 2 O 7 +Li 2 W 2 O 7 . The proportions of the various structural groupings are determine d from the associated Raman peak areas. Structural groupings characteristic of the highly conducting Li 4 P 2 O 7 and Li 2 W 2 O 7 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.