Strain Engineering Defect Concentrations in Reduced Ceria for Improved Electro-Catalytic Performance.

摘要

Here, the oxygen surface exchange coefficient (k) and film stress of porous lanthanum strontium ferrite (LSF64) thick films were measured between 275-400C and 275-700C, respectively, using a bilayer curvature measurement technique. Similar to bulk samples, the thick film stress magnitudes were close to zero. The magnitude and activation energy of the porous thick film k s were also consistent with low temperature extrapolations of large grained, bulk sample behavior. However, unlike large grained, bulk LSF64 samples that only exhibited measurable chemical stress above 525C, the fine-grained, porous LSF64 thick films studied here exhibited measurable chemical stress over the complete range from 275 to 700C. Further, the porous thin films exhibited a kink in their Arrhenius chemical stress behavior (displaying activation energies of 0.07 eV below at 525C and 0.5 eV above at 525C), suggesting a distinct lattice-dominated chemical stress response above 525C and a distinct grain-boundary-dominated chemical stress response below 525C. This the first time the curvature relaxation method has been used to extract k s from a porous film, the first time simultaneous stress and oxygen surface exchange measurements have been collected on a low-stress sample, and the first time a temperature-induced transition from grain-boundary-dominated chemical expansion to lattice-dominated chemical expansion has been observed.