In this paper we show that mechanochemical approach allows fast synthesis of individual phases with fluorite and perovskite structures and preparation of dual-phase nanocomposites with mixed ionic-electronic conductivity. Binary oxides obtained by mechanosynthesis are frequently metastable compounds which decompose at moderate temperatures before sintering into the dense ceramics. Complex doping provides kinetic stabilization of perovskites and fluorites and allows their sintering into dense ceramics. Moreover, complex doping of structurally different phases makes possible a preparation of compatible compounds for nanocomposites. In all 10 nanocomposites considered here, the chemical interaction (interdiffusion) was found to occur in some degree. Rules are formulated for preparation of composites from compatible compounds. All perovskites and ceria-based composites are likely to be more promising as membrane materials. (c) 2005 Elsevier B.V. All rights reserved.