Temperature Dependence and Gas-Sensing Response of Conduction for Mixed Conducting SrFeyCoz O x Thin Films

Abstract

A series of thin films on sapphire substrates was prepared by laser deposition and the conductance responses to both temperature and gas composition in mixtures were examined. All films exhibited p-type semiconductor behavior with film conductivities at 500°C between 20 and 200 S/cm for films exposed to 100% atm and 0.4-25 S/cm for films exposed to 0.2% At 500°C, thin films of compositions were found to be the most conductive for oxygen partial pressures between atm. and films were found to be the least conductive under these conditions. and films were found to exhibit regions where conductivity exhibited temperature independence between for oxygen concentrations between 0.2 and 100% The temperature independence was interpreted as the result of a balancing of two opposing thermal effects: thermal activation of charge carriers and thermal-induced oxygen stoichiometry changes. For some films, enhanced oxygen sensitivity was observed over narrow regions, and is attributed to cubic perovskite to brownmillerite phase transitions. CO and gases could be detected in background air for conditions where there is negligible temperature dependence of conduction. © 2002 The Electrochemical Society. All rights reserved.