Anomalous diffusion of defects in rutile-titanium dioxide: correlation between ac conductivity and defect structures

This work is concerned with the measurement of conductivity σ(ω), and also permittivity ε(ω), in samples of TiO2 of rutile structure. The electrical response exhibits universal behavior in the form of power-law dependences on frequency, which was labeled as anomalous low-frequency dispersion. In the used measuring conditions, charge transport is due to the diffusion of ionic defects of the bulk material. Two crossover frequencies were found that signal the transition between different diffusing regimes. One of them is restricted to small, structural size regions (ξ∼5 Å), in the same way as localized motion of cations commonly reported for ion-containing glasses. The second diffusing regime is confined inside the regions of nanometer scale (ξ′∼5 nm), which is interpreted in terms of the correlated charge motions in the observed clusters of defects (crystallographic share planes). Therefore, this study highlights the correlation between electrical measurement and structural properties.