title: Oxygen diffusion and surface exchange in the mixed conducting oxides SrTi1-yFeyO3-δ.
abstract: Oxygen transport in the mixed ionic-electronic conducting perovskite-oxides SrTi1-yFeyO3-δ(with y = 0.5 and y = 1.0) was studied by oxygen isotope exchange measurements. Experiments were performed on thin-film samples that were grown by Pulsed Laser Deposition (PLD) on MgO substrates. Isotope penetration profiles were introduced by18O2/16O2exchanges into the plane of the films at various temperatures in the range 773 < T/K < 973 at an oxygen activity aO2= 0.5. Isotope profiles were determined subsequently by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and their analysis yielded tracer diffusion coefficients D* and oxygen surface exchange coefficients k*. Activation energies for oxygen diffusion ΔHD*and surface exchange ΔHk*were obtained. Isothermal values of D* and values of ΔHD*are compared with literature data as a function of Fe content. D* is seen to increase monotonically with Fe content; ΔHD*shows more complex behaviour. D* and ΔHD*are also compared with the predictions of defect-chemical models. Analogous comparisons with literature data for k* and ΔHk*indicate, in contrast to prior studies, no mechanistic difference between electron-poor and electron-rich materials. It is concluded that the single operative mechanism of surface exchange for the entire series of STF compositions requires conduction-band electrons (minority electronic charge-carriers).
authors.affiliation: Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany. desouza@pc.rwth-aachen.de.
authors.forename: Veronika
authors.initials: V
authors.lastname: Metlenko
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: WooChul
authors.initials: W
authors.lastname: Jung
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Sean R
authors.initials: SR
authors.lastname: Bishop
authors.affiliation: Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA and International Institute of Carbon Neutral Energy Research, Kyushu University, Fukuoka 819-0395, Japan.
authors.forename: Harry L
authors.initials: HL
authors.lastname: Tuller
authors.affiliation: Institute of Physical Chemistry, RWTH Aachen University, 52056 Aachen, Germany. desouza@pc.rwth-aachen.de.
authors.forename: Roger A
authors.identifier: http://orcid.org/0000-0001-7721-4128
authors.initials: RA
authors.lastname: De Souza