The effects of Sr substitution on the crystal chemistry, phase stability, and electrochemical performance as cathodes in intermediate-temperature solid oxide fuel cells (IT-SOFCs) of the layered LnBa(1-x)Sr(x)CoCuO(5+delta) (Ln = Nd and Gd) perovskites have been investigated. The LnBa(1-x)Sr(x)CoCuO(5+delta) oxides crystallize in tetragonal P4/mmm symmetry for 0 <= x <= 0.75. The x = 0.75 samples show a significant improvement in electrochemical performance compared to the x = 0 samples for both Ln = Nd and Gd. In an electrolyte (La0.8Sr0.2Ga0.8Mg0.2O2.8)-supported single cell configuration (thickness = 0.50 mm), the Ln = Gd series shows an improved maximum power density from 468 mW cm(-2) for the Sr-free (x = 0) sample to 530 mW cm(-2) for the x = 0.75 sample. In the Ln = Nd system, the x = 0.75 sample shows a maximum power density of 562 mW cm(-2). The Sr substitution was found to have negligible effect on the thermal expansion coefficients (TEC) between the x = 0 and x = 0.75 samples in both series. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.