High Temperature Crystal Chemistry and Oxygen Permeation Properties of the Mixed Ionic–Electronic Conductors LnBaCo2O5 + δ ( Ln = Lanthanide )

Abstract

The high temperature crystal chemistry and oxygen permeation properties of the cation-ordered LnBaCo2 O5+δ perovskite oxides [lanthanide (Ln)=Pr, Nd, and Sm] have been investigated in comparison with the cation-disordered La0.5 Ba0.5 CoO3-δ perovskite. The LnBaCo2 O5+δ (Ln=Pr, Nd, and Sm) oxides exhibit a metal-insulator transition at T<200°C, as evidenced by total conductivity measurements and high temperature X-ray diffraction data and an oxygen vacancy order-disorder transition at T >350°C in air, as evidenced by an orthorhombic to tetragonal transition. At a given temperature, the oxygen permeation flux decreases from Ln=La to Nd to Sm due to the changes in crystal symmetry and lattice strain. The oxygen permeation mechanism in the Ln=Nd is bulk-diffusion-limited rather than surface-exchange-limited for membrane thickness L1≥1 mm.