Three different methods of synthesis of ceria-gadolinia (CGO) nanopowders are presented. We established a technique of the synthesis of uniformly aggregated, agglomerate-free CGO in which ceria-gadolinia composite nano-aggregates (15-40 nm) are prepared by nucleation and crystallization of ceria on the surface of preliminary synthesized, hydrolyzed and ultrasonically de-agglomerated gadolinia (3-17 nm). Nano-size aggregates (12-65 nm) of CGO were produced during subsequent non-isothermal calcination. The incorporation of the small concentrations of gadolinia in the ceria lattice was studied using the electron spin resonance technique. It was confirmed that Gd3+ occupies the sites of both cubic and axial symmetry. With increasing concentration, Gd3+ forms a defect complex with the oxygen vacancy.
