Abstract
The high temperature crystal chemistry and oxygen permeation properties of the cation-ordered perovskite oxides [lanthanide , Nd, and Sm] have been investigated in comparison with the cation-disordered perovskite. The (, Nd, and Sm) oxides exhibit a metal-insulator transition at , as evidenced by total conductivity measurements and high temperature X-ray diffraction data and an oxygen vacancy order–disorder transition at in air, as evidenced by an orthorhombic to tetragonal transition. At a given temperature, the oxygen permeation flux decreases from to Nd to Sm due to the changes in crystal symmetry and lattice strain. The oxygen permeation mechanism in the is bulk-diffusion-limited rather than surface-exchange-limited for membrane thickness .
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