The chemomechanical properties and microstructural stability of nanocrystalline PrxCe1-xO2-delta solid solutions are studied as a function of temperature by in situ X-ray diffraction measurements under oxidizing conditions at P(O-2) similar to 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 PrxCe1-xO2-delta. This is contrary to reports regarding variation of physical and chemical properties with crystallite size. The thermal expansion coefficient, measured under conditions for which PrxCe1-xO2-delta is highly oxygen deficient, was found to be greater than that measured for fully oxidized PrxCe1-xO2-delta, with potential sources of these changes discussed. Moreover, the microstructure of nanocrystalline PrxCe1-xO2-delta is observed to have excellent stability at working temperatures below 800 degrees C. enabled by the inherent microstrain in the structure, highlighting the potential application of this material for solid state electrochemical devices. (C) 2011 Elsevier B.V. All rights reserved.