Conductividad eléctrica y difusión de oxígeno en el sistema Bifevox

We present electrical conductivity measurements of BIFEVOX Bi ₄V_2-xFe_xO_11-y (0≤x≤0.9; 0≤y≤1), in which V (IV) ions have been systematically substituted by Fe (III) ions. Conductivity shows a power law frequency dependence described by the form σ*(ω)= σ_dc[1+(jω/ω_p)ⁿ], known as universal dynamic response. Conversely, the electric modulus shows asymmetric peaks, characterized by stretched exponentials relaxation functions in time domain of the form φ(t)=exp(-(t/τ₀)β). β is determined by the degree of correlation in the ionic motion. It's value, β=0.56±0.03, is almost independent of temperature and iron content. Increasing Fe content leads to an exponential decrease of the conductivity and to an increase of the activation energy of the conduction process from 0.20 to 0.97 eV. These results are discussed in terms of oxygen vacancy ordering upon Fe (III) substitution.