Abstract
Solid solutions with the overall composition PrBaMn2–xCoxO6–δ were extensively studied with respect to their crystal structure, oxygen non-stoichiometry and thermodynamic properties. A multistep synthetic route was successfully applied to obtain single-phase samples, with cobalt solubility limit found to lie within the range 0.33 ≤ x ≤ 0.67. Small amounts of Co3O4 impurity were clearly observed as the leading admixture. The use of high temperature coulometric titration technique revealed tremendous oxygen non-stoichiometry in the oxides studied. Accordingly, possible δ values in PrBaMn2–xCoxO6–δ, under certain external conditions, were found to range from 0.0 to 1.35 and 0.0 to 1.25, for x = 0.11 and x = 0.33, respectively. The observed phenomenon was shown to result in the highest heat values for the reduction of PrBaMn1.89Co0.11O6–δ. A theoretical model of defect equilibration under the varying ambient conditions was developed. Cobalt incorporation was found to be a key factor for the facilitation of oxygen exsolution from the lattice at reduction, and for subsequent intensification of charge disproportionation within a manganese sublattice.
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