Thermodynamics of formation of double perovskites GdBaCo2−xMxO6−δ (M = Fe, Mn; x = 0, 0.2)

Standard enthalpies of formation of GdBaCo2−xMxO5.5 (M = Fe, Mn; x = 0, 0.2) from constituent oxides, ΔoxHi∘, and elements, ΔfHi∘, at 298 K were calculated using dissolution enthalpies of corresponding double perovskites. Both ΔoxHi∘ and ΔfHi∘ were found to decrease in the sequence of GdBaCo2O5.5, GdBaCo1.8Fe0.2O5.5 and GdBaCo1.8Mn0.2O5.5 indicating growth of relative thermodynamic stability of GdBaCo2O5.5 caused by the substitution of Fe or Mn for Co.

► ΔfHi∘ of GdBaCo2−xMxO5.5 (M = Fe, Mn; x = 0, 0.2) at 298 K were determined using solution calorimetry. ► ΔfHi∘ decrease in the sequence of GdBaCo2O5.5, GdBaCo1.8Fe0.2O5.5 and GdBaCo1.8Mn0.2O5.5. ► Substitution of Fe or Mn for Co improves relative thermodynamic stability of GdBaCo2O5.5.