Iron mixed-valence compounds, BaSm(Cu_0.5+xFe_0.5-x)₂O_5+δ. I: synthesis and chemical characterization

Oxygen-deficient BaSm(Cu_0.5+xFe_0.5-x)₂O_5+δ (x = -0.5, -0.45, -0.4, -0.1 and 0.0) double-perovskite samples have been successfully obtained by means of a novel synthesis technique utilizing an Fe/FeO getter encapsulated together with the starting material mixture in an evacuated silica-glass tube. The reducing conditions during the synthesis correspond to an oxygen partial pressure of approx. 7.6 × 10^-16 atm. From X-ray diffraction (XRD), transmission electron micrographs (TEM) and energy-dispersive X-ray (EDX) analyses, the samples have been confirmed to be of essentially single phase. By post-annealing the as-synthesized samples under O₂ or H₂/Ar mixed gas, the amount of excess oxygen was controlled. Approaching δ ≈ 0 required prolonged annealing periods under reducing conditions. Samples having -0.4 < x < -0.1 did not form as a single-phase material under the present synthesis conditions.