Defect structure and redox energetics of NdBaCo2O6-δ

The oxygen content in the double perovskite NdBaCo2O6-δ was measured as a function of oxygen partial pressure (1–10−5 atm) at different temperatures (623–1323 K) using thermogravimetry analysis (TG) and coulometric titration technique. The defect structure model of the oxide studied was proposed and successfully verified using the pO2 – T – δ data, yielding the enthalpies and entropies of the defect reactions involved. Standard enthalpy of formation from elements (ΔfH298∘) was measured for quenched NdBaCo2O6-δ samples with different oxygen content. Regarding the ΔfH298∘(6-δ) dependences, two important observations were made. First, the ΔfH298∘(6-δ) consists of two linear fragments with different slopes reflecting different modes of oxygen exchange, accompanied by either reduction of cobalt from Co+3 to Co+2 or from Co+4 to Co+3 in the ranges 5.0 ≤ 6-δ ≤5.5 and 5.5