Preparation and characterization of nanocrystalline powders of bismuth vanadate

The influence of mechanical activation on the formation of Bi2VO5.5, bismuth vanadate (BiV) phase, was investigated by ball-milling a stoichiometric mixture of bismuth oxide and vanadium pentoxide. The structural evolution of the desired BiV phase, via an intermediate BiVO4 phase, was investigated using X-ray powder diffraction (XRD), differential thermal analysis (DTA) and transmission electron microscopy (TEM). Milling for 54h. yielded monophasic γ-BiV powders with an average crystallite size of 30 nm. The electron paramagnetic resonance (EPR) peaks associated with the V4+ ions are stronger and broader in nanocrystalline (n) BiV than in the conventionally prepared microcrystalline (m) BiV, suggesting that a significant portion of V5+ has been transformed to V4+ during milling. The optical bandgap of n-BiV was found to be higher than that of m-BiV. High density (97% of the theoretical density), fine-grained (average grain-size of 2 μm) ceramics with uniform grain-size distribution could be fabricated using n-BiV powders. These fine-grained ceramics exhibit improved dielectric, pyro and ferroelectric properties.