Hydroxides as precursors of nanocrystalline oxides

The formation of nanocrystalline oxides by hydrolysis is analyzed. X-ray powder diffraction was used to measure atom distribution; when it was crystalline the structure was refined by the Rietveld method Three systems were studied: zirconia, titania and magnesia; they were prepared by using the sol-gel technique. During hydrolysis, the proportions of aquo, hydroxo and oxo bindings determined the initial atom distribution and ifs evolution with temperature. In zirconia, the amorphous structure was fixed by aquo bondings, this structure was obtained in titania samples only at high water to alkoxide molar ratios. In magnesia system, synthesis ions also affected the concentration of these bindings. (C) 1999 Acta Metallurgica Inc.