Here, the chemical oxygen surface exchange coefficient and film stress of porous La0.6Sr0.4FeO3-delta (LSF64) thick films were simultaneously measured in situ between 275-375 degrees C and 275-700 degrees C , respectively, using a bilayer curvature measurement technique. The magnitude and activation energy of the porous LSF64 thick film oxygen surface exchange coefficients were consistent with those from large grained, bulk samples. However, unlike large-grained, dilatometry-tested bulk LSF64 samples that only exhibited measurable chemical stress above 525 degrees C, the fine-grained, curvature-tested porous LSF64 thick films studied here exhibited measurable chemical stress over the complete temperature range from 275 to 700 degrees C. Further, the porous LSF64 thick films exhibited a kink in their Arrhenius chemical stress behavior (displaying activation energies of 0.07 eV below 525 degrees C and 0.5 eV above 525 degrees C), suggesting a distinct lattice-dominated chemical stress response above 525 degrees C and a distinct grain-boundary-dominated chemical stress response below 525 degrees C. (C) The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.