The crystal structure, thermal expansion, and electrochemical properties of the layered perovskite series NdBa1-xSrxCo2O5+delta (x = 0 and 0.5) were investigated to study the effects of substituting Sr for Ba on a layered perovskite oxide. A tetragonal layered perovskite structure was observed in NdBaCo2O5+delta (NBCO), and a tetragonal structure was also observed in NdBa0.5Sr0.5Co2O5+delta (NBSCO) when Sr was substituted into NBCO. The thermal expansion coefficients (TECs) of NBSCO and NBCO were both bigger than 22 x 10(-6) K-1 at 530 degrees C. However, the TEC values for 50 wt% of NBSCO and 50 wt% of Ce0.9Gd0.1O2-delta (CGO91) (NBSCO:50) were 13.2 x 10(-6) K-1 at 600 degrees C and 13.7 x 10(-6) K-1 at 700 degrees C; for 50 wt% of NBCO and 50 wt% of CGO91 (NBCO:50) they were 12.4 x 10(-6) K-1 at 600 degrees C and 12.5 x 10(-6) K-1 at 700 degrees C. The cathode polarizations (Rp) of NBSCO and NBCO on a CGO91 electrolyte were observed to be 0.25 and 0.11 Omega cm(2), respectively, at 700 degrees C. The Rps of composite cathodes in NBSCO:50 and NBCO:50 were 0.061 and 0.038 Omega cm(2), respectively, at 700 degrees C. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.