Citrate gel synthesis and characterization of (ZrO2)0.85(REO1.5)0.15 (RE = Y, Sc) solid solutions

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 °C, 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 °C) → bridging (300–350 °C) → ionic (400–500 °C). The oxide powder resulted from the calcination of the gel at 800 °C 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.