Surface Proton Conduction of Sm-Doped CeO2-δ Thin Film Preferentially Grown on Al2O3 (0001)
Daiki Nishioka, Takashi Tsuchiya, Wataru Namiki, Makoto Takayanagi, Kinya Kawamura, Takeshi Fujita, Ryu Yukawa, Koji Horiba, Hiroshi Kumigashira, Tohru Higuchi
Abstract
Abstract Sm-doped CeO 2- δ (Ce 0.9 Sm 0.1 O 2- δ ; SDC) thin films were prepared on Al 2 O 3 (0001) substrates by radio frequency magnetron sputtering. The prepared thin films were preferentially grown along the [111] direction, with the spacing of the (111) plane ( d 111 ) expanded by 2.6% to compensate for a lattice mismatch against the substrate. The wet-annealed SDC thin film, with the reduced d 111 value, exhibited surface protonic conduction in the low-temperature region below 100 °C. The O1 s photoemission spectrum exhibits H 2 O and OH − peaks on the SDC surface. These results indicate the presence of physisorbed water layers and the generation of protons on the SDC (111) surface with oxygen vacancies. The protons generated on the SDC surface were conducted through a physisorbed water layer by the Grotthuss mechanism.