A temperature drop on exposure to reducing gases for various metal oxide thin films

The temperature drop on exposure to C2H5OH was examined for various metal oxide thin films of In2O3, SnO2, CuO, WO3, ZnO, CeO2(W), CeO2 and TiO2 to study the mechanism. The temperature drop was observed for films of In2O3, SnO2 and WO3, of which the change in electric conductivity ΔG was comparatively large, and the magnitude of the drop increased with ΔG. On the other hand, the temperature drop was not observed clearly for films of ZnO, CeO2(W), CeO2 and TiO2, of which the ΔG was small. The dependence of the temperature drop on sensor temperature was also measured in the range of 300–500°C of sensor temperature for films of In2O3, SnO2 and WO3. It was found that the dependence was nearly expressed as A(T4−T04)×ΔG(T), where T and T0 denote a sensor temperature and a room temperature in Kelvin scale, respectively. The mechanism of the temperature drop was discussed.