By the citrate gel method, (ZrO2)(0.85)(REO1.5)(0.15) (RE = Y, Sc) solid solutions in pure cubic fluorite structure were prepared at relatively low calcination temperatures. The existence of the strong coordination interaction between the -COO- groups of the ligands and metal ions could effectively prevent the segregation of metal ions during the gel formation. Upon heat treatment within 110-500 degreesC, the gel decomposed by multi-steps, with the formation of well-defined intermediate decomposition products, while, the bonding nature between -COO- groups and metal ions changed with temperature: unidentate (110-250 degreesC) --> bridging (300-350 degreesC) --> ionic (400-500 degreesC). The oxide powder resulted from the calcination of the gel at 800 degreesC is an assembly of mesoporous nanoparticles with uniform sizes, but agglomerated in lumps. It was confirmed that the chemical homogeneity, nanoparticle size uniformity and crystallinity, sinterability and electrical conductivity of (ZrO2)(0.85)(REO1.5)(0.15) can be remarkably improved by avoiding the phase separation (solid/liquid) phenomenon during the preparation of the gels. (C) 2004 Elsevier Ltd. All rights reserved.