The crystal chemistry, electrical conductivity, thermal expansion behavior, chemical compatibility, and electrochemical performance of perovskite Nd0.6Sr0.4Co1-xFeyO3-delta (0 <= y <= 0.5) oxides as cathode materials for intermediate temperature solid oxide fuel cells have been investigated. The samples crystallize in an orthorhombic structure, and the lattice parameters and cell volume increase with increasing Fe content y. The degree of oxygen loss on heating to higher temperatures and the thermal expansion coefficient (TEC) decrease with increasing y due to a stronger Fe-O bond. The electrical conductivity decreases with y, and the system exhibits a metal to semiconductor transition at around y = 0.2. The electrocatalytic activity and power density measured with single cells decrease with increasing y due to a decrease in electrical conductivity and oxide ion vacancy concentration. (c) 2005 Elsevier B.V. All rights reserved.