Oxygen content and defect structure of the perovskite La_0.5Ba_0.5CoO_3–δ

Abstract

Perovskite-type complex oxide La0.5Ba0.5CoO3–δ, promising cathode material for solid oxide fuel cells and precursor for synthesis of double perovskite LaBaCo2O6–δ, was prepared as a single-phase material. Its oxygen content was measured by two independent techniques in the temperature range 1000–1100 °C and at oxygen partial pressures corresponding to the stability field of cubic phase. The defect chemistry of this material was studied using the measured δ=f(pO2,T) dependences. The defect structure model based on the localized nature of the electronic defects was proposed and successfully verified.

Defect-Induced Properties and Thermodynamics of La0.5Ba0.5CoO3–δ

“…1; note that the high-temperature data obtained by TG in this work and by coulometric titration in the previous one 25 agree well with each other. A simple defect structure model, based on the oxygen exchange and charge disproportionation reactions (see Table I), with the localized nature of the electronic defects taken into account, was used to obtain the model log 25 This equation was fitted to the experimental data on oxygen nonstoichiometry of La 0.5 Ba 0.5 CoO 3-δ yielding the values of the standard enthalpies, ∆ ○ H , i and entropies, ∆ ○ S , i of defect reactions. To reduce the number of fitting parameters, we used a previously developed approach 25 of assuming the cobalt disproportionation entropy to be equal to zero.…”

“…Defect structure and oxidation thermodynamics.-Let us first describe the defect structure and oxygen exchange thermodynamics of cubic perovskite La 0.5 Ba 0.5 CoO 3-δ for they influence the other properties of this oxide that are discussed in the present work. Previously, we reported the oxygen nonstoichiometry of La 0.5 Ba 0.5 CoO 3-δ measured within a relatively high temperature range (1273-1373) K, 25 whereas for the purpose of this study it is necessary to expand the experimental data to lower temperatures. In this work, variation of the oxygen content in La 0.5 Ba 0.5 CoO 3-δ was measured by means of TG in the temperature range (909-1373) K at oxygen partial pressures corresponding to the stability field of cubic phase as determined in Refs.…”

“…A simple defect structure model, based on the oxygen exchange and charge disproportionation reactions (see Table I), with the localized nature of the electronic defects taken into account, was used to obtain the model log 25 This equation was fitted to the experimental data on oxygen nonstoichiometry of La 0.5 Ba 0.5 CoO 3-δ yielding the values of the standard enthalpies, ∆ ○ H , i and entropies, ∆ ○ S , i of defect reactions. To reduce the number of fitting parameters, we used a previously developed approach 25 of assuming the cobalt disproportionation entropy to be equal to zero. The results of the least squares fit are given in Fig.…”

Redox Thermochemistry, Thermodynamics, and Solar Energy Conversion and Storage Capability of Some Double Perovskite Cobaltites

“…Even the stability of LaBaCo 2 O 6−δ in air is known to contrast with those of the other RBaCo 2 O 6−δ double perovskites, as it forms as a simple (disordered) cubic La 0.5 Ba 0.5 CoO 3−δ perovskite with La and Ba statistically distributed in the A sublattice. The formation of the LaBaCo 2 O 6−δ double perovskite requires low p O 2 and high oxygen vacancy concentrations . Thus, the size difference between Ba 2+ and R 3+ ions, their tendency to order along the crystallographic c -axis, and the preferential oxygen vacancy formation in R layers are closely correlated.…”

“…The formation of the LaBaCo 2 O 6−δ double perovskite requires low p O 2 and high oxygen vacancy concentrations. 71 Thus, the size difference between Ba 2+ and R 3+ ions, their tendency to order along the crystallographic c-axis, and the preferential oxygen vacancy formation in R layers are closely correlated.…”