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 Ln = Pr, Nd, and Sm 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 Sm oxides exhibit a metal-insulator transition at T 200C, as evidenced by total conductivity measurements and high temperature X-ray diffraction data and an oxygen vacancy order-disorder transition at T 350C 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 1.1 mm.