Defect structure and redox energetics of NdBaCo2O6-δ

The oxygen content in the double perovskite NdBaCo2O6-delta 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 pO(2) - T - delta data, yielding the enthalpies and entropies of the defect reactions involved. Standard enthalpy of formation from elements (Delta H-f degrees(298)) was measured for quenched NdBaCo2O6-delta samples with different oxygen content. Regarding the Delta H-f degrees(298)(6-delta) dependences, two important observations were made. First, the Delta H-f degrees(298)(6-delta) 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-delta <= 5.5 and 5.5 < 6-delta < 5.7, respectively. Second, when corrected for the quenching effect arising from the oxygen vacancy disordering, the experimental Delta H-f degrees(298)(6-delta) values and those calculated using the partial molar enthalpy of oxygen, which was evaluated using the defect structure model, agree well with each other. This can be regarded as an independent verification of both the model and the related defect reaction thermodynamics.

Automated summary

The oxygen content and defect reaction thermodynamics of the double perovskite oxide NdBaCo2O6-δ were successfully studied through a combination of experimental measurements and theoretical calculations. The relationship between oxygen content and modes of oxygen exchange was observed, showing good agreement between experimental and calculated values, providing independent verification of the defect structure model.