Defect Structure，Electrical Property and Oxygen Permeation of Ba0.5Sr0.5Co0.8Fe0.2O3-δ

Abstract

A study of oxygen permeation material Ba0.5Sr0.5Co0.8Fe0.2O3-δ（BSCF）is presented. The O2 -TPD，nonstoichiometry（δ），electrical conductivity（σ）and oxygen permeation were investigated. In the experiment of O2 -TPD，three oxygen-releasing peaks are observed：one peak at low temperature is attributed to the absorbed oxygen at the position of V··O，the other two peaks are related with the release of oxygen ions at two different positions in the BSCF crystal lattice. At 470℃，δ reaches minimum and σ achieves maximum：with increasing temperature，absorbed oxygen at the position of V··O is released，resulting in the first peak of O2 -TPD；the rest of absorbed oxygen entered BSCF lattice，causing the decrease of δ；the temperature dependence of the conductivity demonstrates increasing conductivity with temperatures up to a maximum at about 470℃，indicating thermally activated p-type semiconductivity，which changed to metallic conduction behavior above 470℃. Furthermore，the experiment shows that the σ maximum at the heating step is higher than that obtained at cooling step，which can be explained：when heating，some absorbed oxygen at the position of V··O enters the lattice，δ decreases and concentration of Co4+&Fe4+ increases，leading to an enhanced p-type conductivity of BSCF；on the other hand，when cooling from high temperature，absorbed oxygen at the position of V··O does not exist. In the experiment of oxygen permeation，BSCF proves to be a suitable material for oxygen-separating at above 850℃，its oxygen permeability JO2 is higher than 1 μmol/cm2 s with air as feed gas and He as sweep gas，the activation energy Ea is 63. 1 kJ/mol.