Correlating High-Temperature Defect and Magnetic Structures with Anomalous Chemical Expansion in an Outstanding PrBa_0.5Sr_0.5Co_1.5Fe_0.5O_6−δ Positrode

Abstract

In this study, PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 6−δ (PBSCF) oxide with a layered double perovskite structure was successfully synthesized and characterized using the combination of X-ray diffraction (XRD) and energy-dispersive X-ray (EDX) methods. Oxygen content and electrical conductivity of PBSCF were measured at elevated temperatures and variable oxygen partial pressures. The corresponding experimental data were successfully analyzed using earlier proposed defect formation and transport models; the obtained results were additionally supported by magnetic experiments. The studied oxide was found to possess weak superstructural ordering at low δ values. Additionally, a noticeable chemical expansion anomaly was uncovered for PBSCF. Currently existing models of chemical deformation in nonstoichiometric oxides were shown to be inefficient for interpreting the data obtained, although a reasonable explanation was proposed on the basis of a more fundamental approach. Nevertheless, the peculiarity revealed was shown to be crucial for providing enhanced ionic mobility for oxygen anions in the PBSCF lattice, thus giving a reasonable explanation to the known superiority of PBSCF as a positrode material when compared to other layered cobaltites.