Enthalpies of formation of RCoO3-δ (R = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y) perovskite cobaltites

Standard enthalpies of formation at 298.15 K, Δ f H 298 . 15 ∘ , for RCoO _3-δ (R = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y) perovskite-type rare-earth cobaltites were obtained from the combined results of drop and reduction calorimetry. The relationship between the oxygen nonstoichiometry, δ, and thermodynamics of RCoO _3-δ was discussed. The fact that RCoO _3-δ with smaller ionic radius of R ³⁺ tend to be less stable, having more positive enthalpy of formation from binary oxides (CoO and R ₂O ₃), Δ f , o x H 298 . 15 ∘ , was confirmed for all the studied RCoO _3-δ. Drop calorimetry results were also used in discussing, comparing and assessing the literature heat capacity, C p T , data for RCoO _3-δ (R ≠ Y). For YCoO _3-δ, both Δ f H 298 . 15 ∘ and C p T were obtained for the first time solely from the drop calorimetric results; Δ f H 298 . 15 ∘ values determined by two different methods perfectly agree with each other. The reference data and C p T of RCoO _3-δ were used to calculate Δ f H 298 . 15 ∘ from the published EMF measurement results so as to compare the available Δ f , o x H 298 . 15 ∘ (RCoO _3-δ) values. An unusual dependence of Δ f H 298 . 15 ∘ (LaCoO _3-δ) on its heat treatment history was identified and supported by the additional isoperibolic solution calorimetry measurements.