RAMAN-SPECTROSCOPY OF HTAMO6.XH2O (M=W AND TE) PYROCHLORES AND THEIR POTASSIUM PRECURSORS

A room temperature Raman study has been performed on polycrystalline samples of HTaWO6.xH2O and HTaTeO6.xH2O, protonic conductors, and, for comparison, on their respective potassium precursors. The hydrated and dehydrated forms of all four compounds, as well as the deuterated Ta-W pyrochlore, have been investigated with reference to host structure vibrations, which fall mainly below 1000 cm-1, and to internal modes of H2O or D2O molecules. A comparative analysis of all these vibrations, in particular the OH stretching mode, indicates that a minimum interaction occurs between water and other species in HTaWO6.H2O. These spectroscopic findings would exclude a direct role of the water molecule in the proton diffusion mechanism, via the formation of H3O+ species.