title: Role of Associated Defects in Oxygen Ion Conduction and Surface Exchange Reaction for Epitaxial Samaria-Doped Ceria Thin Films as Catalytic Coatings.
abstract: Samaria-doped ceria (SDC) thin films are particularly important for energy and electronic applications such as microsolid oxide fuel cells, electrolyzers, sensors, and memristors. In this paper, we report a comparative study investigating ionic conductivity and surface reactions for well-grown epitaxial SDC films varying the samaria doping concentration. With increasing doping above 20 mol % of samaria, an enhancement in the defect association is observed by Raman spectroscopy. The role of such associated defects on the films̀ oxygen ion transport and exchange is investigated by electrochemical impedance spectroscopy and electrochemical strain microscopy (ESM). The measurements reveal that the ionic transport has a sharp maximum in ionic conductivity and drops in its activation energy down to 0.6 eV for 20 mol % doping. Increasing the doping concentration further up to 40 mol %, it raises the activation energy substantially by a factor of 2. We ascribe the sluggish transport kinetics to the "bulk" ionic-near ordering in case of the heavily doped epitaxial films. Analysis of the ESM first-order reversal curve measurements indicates that these associated defects may have a beneficial role by lowering the activation of the oxygen exchange "surface" reaction for heavily doped 40 mol % of samaria. In a model experiment, through a solid solution series of samaria doped ceria epitaxial films, we reveal that the occurrence of associated defects in the bulk affects the surface charging state of the SDC films to increase the exchange rates. The implication of these findings is the design of coatings with tuned oxygen surface exchange by controlling the bulk associated clusters for future electrocatalytic applications.
authors.forename: Nan
authors.initials: N
authors.lastname: Yang
authors.affiliation: Electrochemical Materials, ETH Zurich , Zurich, 8093, Switzerland.
authors.forename: Yanuo
authors.initials: Y
authors.lastname: Shi
authors.affiliation: Electrochemical Materials, ETH Zurich , Zurich, 8093, Switzerland.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Schweiger
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Evgheni
authors.initials: E
authors.lastname: Strelcov
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Alex
authors.initials: A
authors.lastname: Belianinov
authors.forename: Vittorio
authors.initials: V
authors.lastname: Foglietti
authors.affiliation: National Research Council CNR-SPIN, University of Salerno , Fisciano, Salerno I-84084, Italy.
authors.forename: Pasquale
authors.initials: P
authors.lastname: Orgiani
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Balestrino
authors.affiliation: Center for Nanophase Materials Sciences, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Sergei V
authors.initials: SV
authors.lastname: Kalinin
authors.affiliation: Electrochemical Materials, ETH Zurich , Zurich, 8093, Switzerland.
authors.forename: Jennifer L M
authors.initials: JL
authors.lastname: Rupp
authors.forename: Carmela
authors.initials: C
authors.lastname: Aruta
keywords: Raman; defect associations; doped ceria; electrochemical strain microscopy; epitaxial thin films