The effect of Mn+ cation doping on the crystal chemistry, thermal expansion coefficient (TEC), electrical conductivity, and electrochemical performance in solid oxide fuel cells (SOFC) of the Nd0.6Sr0.4Co0.8M0.2O3-delta (M=Ti, Cr, Mn, Fe, Co, and Cu) cathodes has been investigated. The samples form single-phase solid solutions with an orthorhombic perovskite structure. The degree of oxygen loss at high temperatures, TEC, and electrical conductivity decrease with the substitution of Mn+ ions for Co3+/4+ due to an increase in the thermal stability and bond strength and a decrease in the metal-oxygen covalency. The electrocatalytic activity measured with single cell SOFC decreases with Mn+ doping due to a decrease in the oxygen exchange, oxygen mobility, and charge transfer reaction, resulting from a decrease in the electronic conductivity and the oxide ion vacancy concentration. (C) 2007 Elsevier B.V. All rights reserved.