Surface proton conduction below 100 degrees C of Ce0.80Sm0.20O2-delta thin film with oxygen vacancies

Ce0.80Sm0.20O2-delta thin films with (111) orientation were prepared on (0001) Al2O3 substrates by RF magnetron sputtering. The Ce3+ valence ratios, which are closely related to the oxygen vacancies' concentration, of the as-deposited and wet-annealed thin films were 37.8% and 29.3%, respectively. These thin films exhibited oxygen ion related conduction in the medium-temperature region of 800 to 200 degrees C. Below 100 degrees C, the conductivity (sigma) of the wet-annealed thin film increased as the temperature (7) decreased and the sigma T value was similar to 1.0 S cm(-1) K at 25 T. The O 1s photoemission spectrum exhibited H2O and OH- peaks on the surface. The above results indicate that the protons on the surface of the wet-annealed thin film actively migrated through the physisorbed water layer by the Grotthuss mechanism. (C) 2022 The Japan Society of Applied Physics