Effects of preparation parameters on oxygen stoichiometry in Bi4V2O11-δ

The effects of various preparation parameters on vanadium reduction in Bi(4)V(2)O(11-delta) have been investigated using EPR, (51)V MAS solid state NMR and UV diffuse-reflectance spectroscopies and also SQUID magnetometry and powder neutron diffraction. The results confirm that a greater amount of vanadium reduction is observed in rapidly quenched samples and that significant oxidation occurs when samples are slow cooled. Evidence for spin-spin dipolar coupling is seen in the EPR patterns while uncoupled V(4+) spins contribute to weak paramagnetic behaviour. Band gaps of around 2 eV from the UV data suggest there may be a significant electronic component to low temperature conductivities. The (51)V NMR data are not inconsistent with the presence of mainly distorted octahedral and tetrahedral coordinations for vanadium.