EFFECTS OF PREPARATION PARAMETERS ON OXYGEN STOICHIOMETRY IN BI4V2O11-DELTA

The effects of various preparation parameters on vanadium reduction in Bi4V2O11-delta have been investigated using EPR, V-51 MAS solid state NMR and UV diffuse-reflectance spectroscopies and also SQUID magnetom etry and powder neutron diffraction. The results confirm that a greate r amount of vanadium reduction is observed in rapidly quenched samples and that significant oxidation occurs when samples are slow cooled. E vidence for spin-spin dipolar coupling is seen in the EPR patterns whi le uncoupled V4+ spins contribute to weak paramagnetic behaviour. Band gaps of around 2 eV from the UV data suggest there may be a significa nt electronic component to low temperature conductivities. The V-51 NM R data are not inconsistent with the presence of mainly distorted octa hedral and tetrahedral coordinations for vanadium.