Abstract
The structure, oxygen non-stoichiometry, and defect equilibrium in perovskite-type Sr1−xCexFeO3−δ (x = 0.05, 0.10, 0.15, 0.20) were studied. X-ray diffraction showed the formation of a cubic structure for all compositions. The electron diffraction detected an incommensurate structure with a modulation wave vector 0.41 a* in compositions with x ≥ 0.10. The phenomenon is assumed to originate from a strong steric disturbance attributed to a large difference in ionic radii of cerium and strontium. The data on the oxygen content acquired in wide ranges of oxygen partial pressure and temperature were used for the modeling of defect equilibrium in oxides. A part of anion vacancies in Sr1−xCexFeO3−δ was found to be inaccessible for oxygen ions. The main factors of cerium substitution impact on the thermodynamic parameters of defect formation reactions in Sr1−xCexFeO3−δ were revealed to be lattice contraction, steric disturbance, and cerium reduction to Ce3+. The concentration of Ce3+ ions in Sr1−xCexFeO3−δ under reducing conditions was found to be substantially greater than that of Fe2+. Interrelations between thermodynamic quantities of oxygen in Sr1−xCexFeO3−δ and thermodynamic parameters of defect formation reactions were considered.
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