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Crystal structure, thermogravimetry (TG), thermal expansion coefficient (TEC), electrical conductivity and AC impedance of (Ba0.5Sr0.5)(1-x)LaxCo0.8Fe0.2O3-delta (BSLCF; 0.05 <= x <= 0.20) were studied in relation to their potential use as intermediate temperature solid oxide fuel cell (IT-SOFC) cathode. A single cubic pervoskite was observed by X-ray diffraction (XRD). The TEC of BSLCF was increasing slightly with the increasing content of La, and all the compounds showed abnormal expansion at high temperature. Proved by the TG result, it was associated with the loss of lattice oxygen. The electrical conductivity, which is the main defect of Ba0.5Sr0.5 Co0.8Fe0.2O3-delta (BSCF), was improved by La doping, e.g., the compound of x = 0.20 demonstrated a conductivity of sigma = 376 S cm(-1) at 392 degrees C. The increase of electrical conductivity resulted from the increased concentration of charge carrier induced by La doping. In addition, the AC impedance revealed the better electrochemical performance of BSLCF. For example, at 500 degrees C, the sample with composition x = 0.15 yielded the resistance values of 2.12 Omega cm(2), which was only 46% of BSCF. (C) 2007 Elsevier Ltd. All rights reserved.