Multiphase transformations controlled by ostwald's rule in nanostructured Ce(0.5)Zr(0.5)O(2) powders prepared by a modified Pechini route.

ABSTRACT

The thermal stability of nanostructured Ce(0.5)Zr(0.5)O(2) powders prepared by the Pechini method was studied on the nanometric scale by X-ray diffraction (XRD), energy-dispersive spectrometry (EDS), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), and Raman techniques. Obtained results demonstrate that amorphous powders coming from the thermal decomposition of the precursor transform into the stable crystalline state through one highly disordered and metastable intermediate. This is a new example of successive reactions controlled by Ostwald's rule in inorganic systems. At low calcination temperatures, the combination of Raman spectroscopy, high-resolution electron microscopy, and EDS nanoanalysis showed the formation from the precursor powder of a disordered pseudocubic phase. At 900 degrees C, metastable T' and stable T and C phases were detected in XRD patterns. As increasing temperature, crystallites growth and proportions of stable T and C phases increased at the expense of the T' phase, which completely disappeared at 1300 degrees C. In analyzed samples, the Raman technique and (crystal by crystal) EDS nanoanalyses were used to detect local phase inhomogeneity. Compositions and relative percentages of phases were investigated by XRD Rietveld analysis and discussed in terms of phase diagrams previously reported.