Oxygen Surface Exchange in Mixed Ionic Electronic Conductors: Application to La[sub 0.5]Sr[sub 0.5]Fe[sub 0.8]Ga[sub 0.2]O[sub 3−δ]

Abstract

We propose an oxygen surface exchange model in which the effect of vacancies at the gas-mixed ionic electronic conductor interface are included and apply the model to isotope exchange, oxygen permeability, and electrical conductivity relaxation. We deduce relationships between the surface-exchange coefficients associated with these phenomena and extend the treatment of the conductivity relaxation to large changes in oxygen partial pressure, where the commonly used assumption of first order reaction rate breaks down. We apply the model to interpret the permeation and electrical conductivity relaxation measurements in La 0.5 Sr 0.5 Fe 0.8 Ga 0.2 O 3Ϫ␦ . Transport in the material is almost completely surface limited, and data were interpreted in terms of a single surface-exchange coefficient.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.238.7.43 Downloaded on 2014-11-17 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.238.7.43 Downloaded on 2014-11-17 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 130.238.7.43 Downloaded on 2014-11-17 to IP

Kinetics and Mechanisms of Oxygen Surface Exchange on La[sub 0.6]Sr[sub 0.4]FeO[sub 3−δ] Thin Films

“…At t = 0, the oxygen partial pressure is suddenly changed. Because the deposited film is much thinner than L c , transport of oxygen into or out of the material is limited only by the surface exchange process, and the transport equation can be described by a simple mass balance on the sample surface given by 19 A…”

“…For instance, the simplest possible scheme of the process, assuming that it is a one-step process between an oxygen molecule and two vacancies ͑scheme 1͒ predicts a wrong P O 2 dependence. Many two-step mechanisms have been suggested in literature [19][20][21]25,27,35,36 for similar materials, where the first step is either dissociative adsorption on two vacancies ͑scheme 2͒, 20 dissociative adsorption on some surface site ͑scheme 3͒ 21,27 or a dissociative adsorption involving a charge transfer ͑schemes 4,5͒. 21,25,27,35 None of these predict the here-observed P O 2 dependence.…”

“…23 The series of elementary steps that can vary from material to material are not yet well understood, and a significant number of mechanisms have been suggested by different authors. 14,[19][20][21][24][25][26][27] In the following, possible reasonable one-, two-, and three-step reaction mechanisms for the incorporation of oxygen in LSF are discussed.One-step mechanism.-In the simplest possible model, one can assume that the surface reaction, Eq. 17 is itself an elementary reaction corresponding to direct incorporation of oxygen into vacancies with the simultaneous oxidation of B ions ͑formation of electron holes on the iron site͒.…”

Novel Low Temperature Solid State Fuel Cells

“…To obtain oxygen transport information from the impedance spectra, the first order surface exchange kinetics for the dense thin film can be expressed as 15,16 1    RC…”

EFFECTS OF SINTERING TEMPERATURE ON THE PERFORMANCE OF SrSc0.1Co0.9O3-δOXYGEN SEMIPERMEABLE MEMBRANE

“…Recently, several studies were carried out by different groups to elucidate its importance and to address the dependence of the oxygen permeation on the microstructure (Diethelm et al, 2005;Zhang et al, 1999;Etchegoyen et al, 2006;Kim et al, 2000;Kharton et al, 2000;Kharton et al, 2001;Kharton et al, 2002;Arnold et al, 2008;Zeng et al, 2007;Shaula et al, 2005). Different perovskite systems were studied in many of these reports; however, no clear trend was visible relative to whether the transport along grain boundaries displays a barrier, or acts as a pathway for fast oxygen transport.…”