Enhancement of oxygen surface kinetics of SrTiO3 by alkaline earth metal oxides

The kinetics of oxygen incorporation into semiconducting metal oxides such as strontium titanate are of particular interest for an application as a fast resistive-type oxygen sensor operating at high temperatures (T > 600 °C), e.g. in automotive exhaust gas monitoring.Based on a frequency-domain analysis of the response signal (resistance R) obtained from an electrically contacted sample exposed to a modulated oxygen partial pressure pO2 in a fast kinetic measurement setup, the surface transfer controlled response behaviour of undoped and Fe-doped SrTiO3 single crystals with thicknesses in the order of d = 45–125 μm was investigated with regard to the effect of thin PVD layers with alkaline earth (Ca, Sr, Ba) metal oxide compounds.The results of this electrical characterisation are compared with results obtained from 18O tracer exchange experiments and subsequent depth profile analysis by secondary ion mass spectrometry (SIMS). Both the electrical measurements and the 18O self-diffusion experiments revealed an enhancement of oxygen surface exchange kinetics in the case of all three alkaline earth metal oxides investigated.