Oxygen nonstoichiometry in LnBaFe2O5+ across Ln = Nd, Sm, Gd

In double-cell perovskites LnBaFe2O5+w, only lanthanoids Ln ?= ?Pr to Gd support wide equilibrium nonstoichiometry w from 0 >0.5. This study investigates point-defect equilibria behind the variation in along ?Nd, Sm, by quenching oxides flowing gas of controlled oxygen partial pressures and temperatures. The experimental data as a function pO2 T are least-squares fit via standard enthalpies entropies defect-equilibrium reactions formation for electronic-defect pair e? h• anion-Frenkel Oi?? vO••, Fe2+ oxidation. NdBaFe2O5+w is closest behaving pure undoped oxide at 1000 ?°C, where it has single plateau versus plot ?0.5 level. A second plateau, ?0, emerges lower smaller Sm increase size difference Ba, their defect show two plateaus even ?°C. temperature-dependent across this series therefore approximated formal Ln3+ Ba2+ donor-doping model, results presented Brouwer diagrams concentrations. decrease constant KaF due decreasing ionic Nd3+ towards Gd3+ magnified upon temperature that feeds entropy disorder; 400 ?Nd ?10?5.4, 10?15.0 10?24.3.