Nanocrystalline Ce1-xYxO2-x/2 (0≤x≤0.35) oxides via carbonate precipitation:: Synthesis and characterization

A novel carbonate (co)precipitation method, employing nitrates as the starting salts and ammonium carbonate as the precipitant, has been used to synthesize nanocrystalline CeO2 and Ce1-xYxO2-x/2 (x less than or equal to 0.35) solid-solutions. The resultant powders are characterized by elemental analysis, differential thermal analysis/thermogravimetry (DTA/TG), X-ray diffractometry (XRD), Brunauer-Emmett-Teller (BET) analysis, and high-resolution scanning electron microscopy (FIRSEM). Due to the direct formation of carbonate solid-solutions during precipitation, Ce1-xO2-x/2 solid-solution oxides are formed directly during calcination at a very low temperature of similar to300 degreesC for 2 h. The thus-produced oxide nanopowders are essentially non-agglomerated, as revealed by BET in conjunction with XRD analysis. The solubility Of YO1.5 in CeO2 is determined via XRD to be somewhere in the range from 27 to 35 mol%, from which a Y2O3-related type-C phase appears in the final product. Y3+-doping promotes the formation of spherical nanoparticles, retards thermal decomposition of the precursors, and suppresses significantly crystallite coarsening of the oxides during calcination. The activation energy for crystallite coarsening increases gradually from 68.7 kJmol(-1) for pure CeO2 to 138.6 kJ mol(-1) for CeO2 doped with 35 mol% YO1.5. The dopant effects on crystallite coarsening is elaborated from the view point of solid-state chemistry. (C) 2002 Elsevier Science (USA).