Doped ceria compounds find application as electrolytes in solid oxide fuel cells, thanks to their high ionic conductivity at intermediate and high temperature. In a recent X-ray high temperature investigation we observed the transformation from C-type (Y2O3-like) to fluorite (CeO2-like) in highly doped compounds. This conclusion, though, was drawn by monitoring a cation-related parameter, to which X-rays are very sensitive. Since the major interest in these compounds is related to the distribution of oxygen vacancies, we need high resolution neutron powder diffraction in order to accurately determine the O position at high temperature and the distribution of oxygen vacancies (oxygen occupation factors). The determination of the possible oxygen redistribution at high temperature has strong impact on the transport properties and can be precious information or tailoring the synthesis of the material.