This study presents structural and defect properties as function of doping, temperature and pO(2) in (La1-xSrx)(0.99) Co0.6+xNi0.4-xO3-delta (x=0; 0.1; 0.2; 0.3; 0.4). Thermograviomertric analysis showed a linear increase in 6 with both T and x in the high temperature regime. The onset temperature of reduction was seen to increase with x which was confirmed with dilatometry and XANES. XANES measurements further indicated that reduction was exclusively associated with cobalt. A transition from polaronic to itinerant electronic conduction was measured with increasing x ranging from 2000-3500 Scm(-1) in the intermediate SOFC temperature range of 500-800 degrees C. The polarisation resistance when used as porous SOFC cathodes was measured to decrease with x. The activation energy of about 1.8 eV for all electrodes but (La0.6Sr0.4)(0.99) CoO3-delta, for which it was about 1 eV. (c) 2008 Elsevier B.V. All rights reserved.