Evaluation of the AC conductivity and dielectric properties of YBaCo2O5±δ thin films at low temperatures

Textured YBaCo2O5±δ thin films were fabricated on (001)-oriented SrTiO3 substrates by dc magnetron sputtering. AC conductivity and dielectric properties of the films are studied in the frequency range 40 Hz-1 MHz and temperatures varying between 30 and 320 K. The frequency dependent AC conductivity is well described by the Jonscher' dynamical law σac(ω) = σdc + Aωs. It is verified that the frequency exponent s has values ≤ 1. The value of s decreases with increasing temperature, suggesting hopping conduction mechanism. The activation energy for relaxation process ended up being 0.152 eV. It is also found that the AC conductivity is a thermally activated process with AC activation energy decreasing with increasing frequency. High values (∼104) are found for the real part of the dielectric permittivity on a wide temperature range. Moreover, the dependence of the permittivity on the frequency is weak over the entire experimental range and its value decreases with increasing temperature.