Investigation of Mixed Conductor BaCo_(0.7)Fe_(0.3-x)Y_xO_(3-δ) with High Oxygen Permeability

摘要

Cubic BaCo_(0.7)Fe_(0.3-x)Y_xO_(3-δ) (BCFY, × = 0.08-0.2) was prepared by the conventional solid state reaction route as oxygen permeation membranes. The effects of Y-doping on the crystal structure, electrical conductivity, and oxygen permeability are investigated, and the factors influencing the activation energy of oxygen migration are discussed from the viewpoints of metal-oxygen bonding energy and geometric lattice structure. Y-substitution decreases the electrical conductivity but increases the oxygen vacancy concentration of BCFY samples. Nevertheless, the oxygen permeability decreases with increasing Y-doping level. Both the strong Y-O bonding energy and the decreased critical radius (re) with Y-doping should be responsible for the increased activation energy. First principle calculation reveals that Y-doping results in the nonequivalent positions of the mobile oxygen ions and thus limits the oxygen ion diffusion passages. BaCo_(0.7)Fe_(0.3-x)Y_xO_(3-δ) membrane exhibits a high oxygen permeability of 1.73 mL min~(-1) cm~(-2) at 900 °C, thus being a promising candidate material for oxygen separation or POM applications.