Effects of preparation parameters on oxygen stoichiometry in Bi4V2O11–δ

Abstract

The effects of various preparation parameters on vanadium reduction in Bi₄V₂O_11–δhave been investigated using EPR, ⁵¹V 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 V⁴⁺ 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 ⁵¹V NMR data are not inconsistent with the presence of mainly distorted octahedral and tetrahedral coordinations for vanadium.