A temperature-dependent Mossbauer study of Fe-57 in the vanadium pentoxide/vanadium bronze oxide systems

Our previous study involving V2O5 doped with various concentrations of Fe h as shown that there are two sites present in the V2O5 lattice, and two site s present in the vanadium oxide bronze lattice. This study further investig ates the behaviour of the hyperfine parameters of the Fe-57 ions at these s ites as a function of temperature. Temperature-dependent Mossbauer spectra ranging from room temperature to 573 K were obtained on samples of V2O5 con taining 5%, 15% and 80% Fe. The isomer shifts of the various components dis play the usual second order Doppler shift as a function of temperature, and no significant changes were observed in the magnitude of the quadrupole sp littings. From the Duncan-Golding correlation diagram, the valence states o f the Fe ions are found to be 3+. No component was observed with increasing temperature which could be correlated with the population of Fe2+ states. It therefore seems probable that the semiconducting properties of vanadium pentoxide containing Fe are associated with electron hopping between the V4 + and V5+ valence sites rather than in the Fe3+ and Fe2+ valence sites.