Abstract

(ZrO₂)_0.85(REO_1.5)_0.15 (RE = Sc, Y) solid solutions in a pure cubic fluorite structure with uniform grain sizes ranging from nanometers to microns have been synthesized by a Pechini-type sol–gel method, using weakly cross-linked polymers. Metal nitrates, poly(ethylene glycol) and carboxylic acids such as acetic acid and formic acid, have been utilized to make the homogeneous polymer precursor solutions. Owing to its stronger acidity and coordinating capability, formic acid seems more effective in preventing the metal hydroxides segregating from the precursor solutions than does acetic acid during the gel formation. The Sc-doped zirconia derived from the formic acid-containing gel could achieve good-crystallization in the pure cubic phase at sintering temperatures as low as 1000 °C. Gel-calcined powders at 800 °C are mesoporous nanoparticles with narrow size distribution, and show a cubic structure attributed to the crystallite size effect. The polymeric precursor compositions display considerable impact on the gel formation, powder reactivity, crystallization of the sintered body, and finally the ionic conductivity of the grain boundary. However, the bulk ionic conductivity is dependent on the sintering temperature and variety of the dopants, rather than on the precursor compositions. Both the bulk and grain boundary conductivities increase when the sintering temperature/density are raised.