Redox energetics of perovskite-related La(B sub(1 - x)B' sub(x))O sub(3 - delta ) oxides where BB' is FeCo, MnCo, MnNi and CoCu

The enthalpy of oxidation of La(B sub(1 - x)B' sub(x))O sub(3 - delta ) (x = 0.25 and 0.75 for BB' = FeCo, MnCo, MnNi and x = 0.2 for BB' = CoCu) has been derived using solid solution models to analyse thermogravimetric measurements of oxygen non-stoichiometry vs. log(pO sub(2)) at 1273 K. For selected samples the enthalpy of oxidation has also been measured by TG-DSC, and the direct heat measurements agree well with the results from the solution models. The affinity for oxygen decreases when x in La(B sub(1 - x)B' sub(x))O sub(3 - delta ) increases from 0.25 to 0.75. This trend may be extended to a larger range of x-values (x[0,1]) when isotherms from the literature are included in the solution modelling. For the materials investigated in this work, the affinity for oxygen decreases in the order Mn sub(0.75)Ni sub(0.25) > Mn sub(0.75)Co sub(0.25) > Fe sub(0.75)Co sub(0.25) (for x = 0.25) and in the order Mn sub(0.25)Co sub(0.75) > Fe sub(0.25)Co sub(0.75) > Mn sub(0.25)Ni sub(0.75) (for x = 0.75). The Co sub(0.80)Cu sub(0.20) containing material has the smallest affinity for oxygen among all the samples.