Oxygen Release from Grossly Nonstoichiometric SrCo_0.8Fe_0.2O_3−δ Perovskite in Isostoichiometric Mode

Abstract

The kinetics of oxygen release from grossly nonstoichiometric perovskite SrCo0.8Fe0.2O3−δ (SCF) with mixed conductivity chosen as a model object was studied for the first time using the oxygen partial pressure relaxation technique. The use of isostoichiometric conditions during the investigation of the oxygen exchange in SCF characterized by a wide homogeneity region made it possible to get information that cannot be obtained using traditional measurements under isobaric conditions. This approach allowed us to discover a kinetic compensation effect: successive oxygen release from SCF was found to result simultaneously in the increase of the apparent activation energy and pre-exponential factor of the reaction rate.

Oxygen Exchange in MIEC Perovskite Oxide La0.6Sr0.4Co0.2Fe0.8O3−δ: Kinetic and Equilibrium Parameters and Their Interrelation

“…This approach is based on the consideration of the MIEC oxides as homologous δ-series, based on the similarity and at the same time the difference of two states of one oxide with δ 1 ≠ δ 2 with temperature and oxygen partial pressure changes. In refs , , and , the authors used this approach to observe changes in the kinetic and thermodynamic properties of MIEC oxides in isostoichiometric cross sections (δ = const), which confirmed the possibility of considering such compositions as homologous series (δ-homologues).…”

“…This result is in a good agreement with the literature data, , in which the change in the Gibbs energy (μO 2 oxide (δ)) in ferrites is almost completely determined by the entropy coefficient, which is caused by the Fe 3+ /Fe 4+ disorder in the oxide lattice. At the same time, in the cobaltites considered in detail in the papers, ,,, the dependences of the activation enthalpy R 0 on δ are completely determined by the component of the partial molar enthalpy in μO 2 oxide (δ).…”

“…This result is in a good agreement with the literature data, 45,57 in which the change in the Gibbs energy (μO 2 oxide (δ)) in ferrites is almost completely determined by the entropy coefficient, which is caused by the Fe 3+ /Fe 4+ disorder in the oxide lattice. At the same time, in the cobaltites considered in detail in the papers, 24,28,29,33 the dependences of the activation enthalpy R 0 on δ are completely determined by the component of the partial molar enthalpy in μO 2 oxide (δ). It should be understood that in the formal definition of the effective Gibbs activation energy R 0 , defined as −RT ln R 0 , there are summands having an effective entropic form arising due to constant coefficients in R 0 .…”

Activation in the rate of oxygen release of Sr0.8Ca0.2FeO3−δ through removal of secondary surface species with thermal treatment in a CO2-free atmosphere

“…This is consistent with our previous results showing an increase in the rate of oxygen release, and hence the amount of oxygen released within a given time with increasing cycle number. 14 The observed rates of the oxygen release and uptake can be quantified by fitting the change in the oxygen non-stoichiometry Δ δ ( eqn (4) ) with an exponential first-order decay function, 54 as defined in eqn (5) and (6) for the reduction and oxidation steps, respectively: …”

Relation between oxygen stoichiometry and thermodynamic properties and the electronic structure of nonstoichiometric perovskite La0.6Sr0.4CoO3−δ

“…are characteristic of cobalt-containing perovskites. 6,17,22,23 It is worth noting that the thermodynamic properties of such oxides are poorly described within the model of ideal solution of point defects. The authors [3][4][5][6] have made an assumption that the electronic structure of cobalt-containing oxides has metal-like character with delocalized electrons in the partially populated broad conduction band.…”