The crystal chemistry, thermal expansion behavior, electrical conductivity, chemical compatibility, and electrochemical performance in intermediate temperature solid oxide fuel cells (SOFCs) of Nd1-xSrxCoO3-delta (0 less than or equal to x less than or equal to 0.5) perovskite oxides have been investigated. The samples crystallize in an orthorhombic structure, and the lattice volume increases with increasing Sr content, x. The thermal expansion coefficient decreases with x, reaches a minimum at x = 0.3, and then increases. The electrical conductivity increases with x, and the system exhibits a semiconductor-to-metal transition at around x = 0.3. The electrocatalytic activity and power density increase with increasing x, reaches a maximum around x = 0.4, and then decreases due to an interfacial reaction of the x = 0.5 sample with the electrolyte. The x = 0.4 sample shows a maximum power density value of 0.24 W/cm(2) at 800degreesC in single cells fabricated with the La0.8Sr0.2Ga0.8Mg0.2O2.8 electrolyte and Ni-Ce0.9Gd0.1O1.95 cermet anode. (C) 2004 The Electrochemical Society.