We aim determining the concentration of oxygen vacancies due to dynamic equilibrium with a reducing atmosphere as a function of doping rate as well as the consequent structural distortions in rare earths doped ceria solid solutions (Ce1-xRExO2-x/2-d, x=0, 0.125, 0.25. RE=Yb, Y, Sm, Nd, La) This is fundamental to comprehend their catalytic and transport properties of these materials Samples will be measured in an in-situ cell upon reducing (He/CO 5%) and oxidizing condtions (He/O2 20%) at different temperature raging from RT to 750 °C While it is believed that RE3+ doping should progressively suppress the formation of additional vacancies (δ=0), in a previous XRPD/PDF experiment dedicated to RE=Gd system we demonstrated that d>0 even for high dopant concentrations and we individuated the PDF fingerprints of Vo formations and of the induced structural disorder. In this proposal we desire to extend the investigation to other RE dopants, to map the extension of disorder as a function of RE