Two wet-chemical routes have been used to synthesize Sc2O3 nanopowders from nitrate solutions employing ammonia water (AW) and ammonium hydrogen carbonate (AHC) as the precipitants. The precursors and the resultant oxides are characterized by elemental analysis, X-ray diffractometry, differential thermal analysis/thermogravimetry, high-resolution scanning electron microscopy, and Brunauer-Emmett-Teller analysis. Crystalline gamma-ScOOH.nH(2)O (n approximate to 0.5) is the only phase obtained by the AW method. This phase dehydrates to Sc2O3 at similar to400degreesC, yielding hard aggregated nanocrystalline Sc2O3 powders. Three types of precursors have been synthesized by the AHC method, depending on the AHC/Sc3+ molar ratio (R): amorphous basic carbonate [Sc(OH)CO3.H2O] at R less than or equal to 3, crystalline double carbonate [(NH4)Sc(CO3)(2).H2O] at R greater than or equal to 4, and a mixture of the two phases at 3 < R < 4. Among these precursors, only the basic carbonate shows spherical particle morphology, ultrafine particle size (similar to50 nm), and weak agglomeration. Sc2O3 nanopowders (similar to28 nm) with high surface area (similar to49 m(2)/g) have been prepared by calcining the basic carbonate at 700degreesC for 2 h.