Electron Paramagnetic Resonance study of hopping in CCTO mixed with TiO2

Electron Paramagnetic Resonance (EPR) is used to study the transport properties in CaCu3Ti4O12(CCTO) and its mixtures with TiO2. The temperature dependence of the peak to peak linewidth of the EPR spectra in the temperature range 430 ≤ T ≤ 660 K, is studied for the powders of CCTO, 5% CCTO + 95% TiO2 and 1% CCTO + 99% TiO2. All the samples show a behavior predicted by the Small Polaron Hopping model. This behavior is studied as a function of the TiO2 content, finding an activation energy that decreases with increasing TiO2 concentration. We found that two mechanisms govern the conductivity in these system one, intrinsic to the CCTO, via oxygen vacancies and the other one, which improve the conductivity, related to the polarizability of the Ti-ions at the surface of the grains and mediated by the oxygen vacancies at the surface of the CCTO.