Consistent interpretation of isotope and chemical oxygen exchange relaxation kinetics in SrFeMoO ferrite.

This paper is devoted to the study of phase composition and kinetic and thermodynamic characteristics of Mo-doped strontium ferrite SrFeMoO (SFM15) under oxygen-conducting membrane working conditions. Single-phase SFM15 with a cubic 3̄ structure was synthesized using a ceramic method. It was shown that the molybdenum introduction stabilizes the perovskite cubic structure over a wide range of oxygen pressures and temperatures, preventing the bulk phase transition at high temperatures.

The Brønsted-Evans-Polanyi relationship in oxygen exchange of fuel cell cathode material SrCoTaO with the gas phase.

Perovskite related oxides ABO3-δ exhibiting mixed ionic-electronic conductivity (MIEC) possess large deviations from the oxygen stoichiometry. When providing excellent application potential, this feature also makes it very difficult to study the reaction mechanism between such oxides and molecular oxygen, also known as the oxygen reduction reaction. The complexity of the theoretical interpretation of kinetic experiments originates from the significant dependence of the kinetic and equilibrium properties of MIEC oxides on δ.

Nonstoichiometric oxides as a continuous homologous series: linear free-energy relationship in oxygen exchange.

A novel methodology for the analysis of oxygen exchange in practically important nonstoichiometric oxides with mixed ionic electronic conductivity (MIEC) is suggested. It is based on the fact that the kinetic and thermodynamic properties of such oxides vary continuously with oxygen stoichiometry. This allows MIEC oxides to be considered as a homologous series, with the difference that traditional series are discrete in their chemical composition whereas MIEC oxides are continuous in oxygen stoichiometry.

Relation between oxygen stoichiometry and thermodynamic properties and the electronic structure of nonstoichiometric perovskite LaSrCoO.

Continuous phase diagram 3 - δ - log pO - T of the nonstoichiometric perovskite LaSrCoO was obtained in a gas flow reactor by means of the quasi-equilibrium oxygen release technique. The thermodynamic properties of oxides were determined as a function of oxygen nonstoichiometry. Within the framework of the itinerant electron model, the dependence of the oxide nonstoichiometry on the oxygen activity was related to the density of electronic states near the Fermi level.

Oxygen release technique as a method for the determination of "δ-pO2-T" diagrams for MIEC oxides.

A new approach to the determination of oxygen nonstoichiometry (δ) of MIEC oxides as a continuous function of pO2 at high temperatures was developed. The description of the model allowing one to distinguish the contribution of oxygen released from the samples to the partial pressure of oxygen at the outlet of the continuous-flow fixed-bed reactor after the stepwise change of the oxygen partial pressure of inlet gas from 0.2 to 10(-5) atm and to calculate the dependence of δ on pO2 is presented.