High Temperature Crystal Chemistry and Oxygen Permeation Properties of the Mixed Ionic–Electronic Conductors LnBaCo[sub 2]O[sub 5+δ] (Ln=Lanthanide)

The high temperature crystal chemistry and oxygen permeation properties of the cation-ordered LnBaCo 2 O 5+␦ perovskite oxides ͓lanthanide ͑Ln͒ = Pr, Nd, and Sm͔ have been investigated in comparison with the cation-disordered La 0.5 Ba 0.5 CoO 3-␦ perovskite.The LnBaCo 2 O 5+␦ ͑Ln = Pr, Nd, and Sm͒ oxides exhibit a metal-insulator transition at T Ͻ 200°C, as evidenced by total conductivity measurements and high temperature X-ray diffraction data and an oxygen vacancy order-disorder transition at T Ͼ 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 L Ն 1.1 mm.