Studies on oxygen chemical surface exchange and electrical conduction in thin film nanostructured titania at high temperatures and varying oxygen pressure

Abstract

We report on oxygen surface exchange studies in similar to 450-nm-thick nanocrystalline titania films with an average grain size of similar to 13 nm by electrical conductivity relaxation along with the conductivity measurements at varying temperatures and oxygen partial pressures (pO(2)s). By electrochemical impedance spectroscopy technique, the high temperature conductivity was measured in the pO(2) range from similar to 10(-16) to similar to 10(-6) Pa at temperatures from 973 to 1223 K and activation energy, Delta E(a), for conduction was estimated as similar to 3.23 eV at pO(2) similar to 10(-11) Pa. Under reducing atmosphere (pO(2) < 10(-6) Pa), two distinct n-type conduction regimes were observed and corresponding predominant defects are discussed while, at high pO(2) regime (pO(2) > 10(-6) Pa), ionic conduction appears dominant leading to a conductivity plateau. The surface relaxation was observed to have two independent time constants likely originating from microstructural effects. The surface exchange coefficients are measured as similar to 10(-8)-10(-7) m/s and similar to 10(-9)-10(-8) m/s for each contribution with Delta E(a)s of 2.79 and 1.82 eV, respectively, without much pO(2) dependence across several orders of pO(2) range of similar to 10(-16)-10(-6) Pa in the temperature range between 973 and 12