Dielectric behavior,conduction and EPR active centres in BiVO4 nanoparticles

Bismuth vanadate (BiVO₄) nanomaterials were synthesized by mechano-chemical ball milling method and complementary investigations were devoted to their structures, nanoparticle morphologies and electronic active centres. The dielectric and conductivity behaviour were analysed systematically in wide temperature and frequency ranges to correlate such physical responses with the peculiarities of the samples. Large interfacial polarisations favoured by high specific surfaces of nanoparticles account for a drastic enhancement of the dielectric function in the quasi-static regime. Exhaustive analyses of the dielectric experiments were achieved and account for the main features of dielectric functions and their related relaxation mechanisms. The electrical conductivity is thermally activated with energies in the range 0.1–0.6 eV depending on the sample features. DC conductivity up to 10^–3 S/cm was obtained in well crystallized nanoparticles. Vanadium ions reduction was revealed by EPR spectroscopy with higher concentrations of the active centres (V⁴⁺) in more agglomerated and amorphous nanopowders. The EPR spectral parameters of V⁴⁺ were determined and correlated with the local environments of reduced vanadium ions and the characteristics of their electronic configurations. An insight is also made on the role of active electronic centres (V⁴⁺) on the conduction mechanism in nanostructured BiVO₄.