Chemomechanical properties and microstructural stability of nanocrystalline Pr-doped ceria: An in situ X-ray diffraction investigation

The chemomechanical properties and microstructural stability of nanocrystalline Pr_xCe_1 − xO_2 − δ solid solutions are studied as a function of temperature by in situ X-ray diffraction measurements under oxidizing conditions at P(O₂) ~ 200 mbar. The chemical expansion coefficient of nanocrystalline powder specimens, operative at intermediate temperatures during which Pr⁴⁺ is reduced to Pr³⁺, is found to be similar to that obtained for coarse-grained Pr_xCe_1 − xO_2 − δ. This is contrary to reports regarding variation of physical and chemical properties with crystallite size. The thermal expansion coefficient, measured under conditions for which Pr_xCe_1 − xO_2 − δ is highly oxygen deficient, was found to be greater than that measured for fully oxidized Pr_xCe_1 − xO_2 − δ, with potential sources of these changes discussed. Moreover, the microstructure of nanocrystalline Pr_xCe_1 − xO_2 − δ is observed to have excellent stability at working temperatures below 800 °C, enabled by the inherent microstrain in the structure, highlighting the potential application of this material for solid state electrochemical devices.