Local disorder in yttrium doped ceria (Ce1-xYxO 2-x/2) probed by joint X-ray and neutron powder diffraction

Yttrium doped ceria materials (Ce1-xYxO 2-x/2) are widely studied for their application in Solid Oxide Fuel Cells devices. An anomalous decrease in the isothermal ionic conductivity at increasing Y3+ concentration above a critical value has been observed and attributed to the formation of defect clusters / domains at the nanometric scale, the crystallographic structure of which is still under debate. In this context we present a combined Synchrotron Radiation and Neutron Powder Diffraction study. In particular, neutrons allow to determine accurately oxygen related parameters, the contribution of which in terms of X-ray scattering power is almost negligible when compared to that of cations. The effect of doping on the average structure is investigated using conventional Rietveld analysis, while the Pair Distribution Function (PDF) technique is used to explore structural distortions and the spatial extent of disorder as well. The local structure observed in the real space is not consistent with the mean crystallographic one and is better modeled considering a biphasic model.