Surface proton conduction below 100 °C of Ce_0.80Sm_0.20O_2−δ thin film with oxygen vacancies

Abstract Ce0.80Sm0.20O2−δ 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 °C. Below 100 °C, the conductivity (σ) of the wet-annealed thin film increased as the temperature (T) decreased and the σT value was ∼1.0 S cm−1 K at 25 °C. 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.