Combustion synthesis of nano-crystalline Nd-doped ceria and Nd2O3 and their fractal behavior as studied by small angle X-ray scattering

Nano-crystalline Nd2O3 and Ce0.50Nd0.50O1.75 were synthesized by the gel combustion technique, using glycine as the fuel and the corresponding metal nitrates as oxidants. The products were characterized by XRD to ascertain the phase purity. The crystallite sizes as calculated by X-ray line broadening were found to be about 10 and 35 nm for Nd2O3, obtained from the fuel-deficient and propellant ratios, respectively. It was observed that on 50 mol% doping of NdO1.5 into CeO2 the crystallite sizes reduced to 7 and 12 nm, respectively, for the two ratios. These values for the particle sizes were in close agreement as observed from the TEM images. A remarkable observation was that a partial stabilization of the C-type cubic phase in nano-crystalline Nd2O3 was observed for powders prepared using the fuel-deficient ratio. Small angle X-ray scattering (SAXS) technique show that, unlike the similar type of samples studied previously, the aggregates formed in the present powders exhibit surface-fractal characteristics with fractal dimension (D-s) in the range 2.5-3.0. The basic particle interface is indicated to be diffuse or fuzzy in nature suggesting a continuous variation of density at the boundaries. (C) 2007 Elsevier B.V. All rights reserved.