Crystallization behaviour of TiO2–ZrO2 composite nanoparticles

Nano-composite TiO2–ZrO2 materials were prepared via sol–gel processes by hydrolysis of mixtures of titanium- and zirconium-containing alkoxides with TiO2:ZrO2 ratios of 1:2, 1:1, 2:1, and 10:1. Precipitated powders were dried at room temperature and annealed in ambient air at temperatures between 350 and 500 °C for 4 h. Pure TiO2 and ZrO2 powders were synthesized for comparison. Samples were characterized with X-ray diffraction (XRD) and X-ray absorption near edge fine structure (XANES). The detailed analysis of those data provides the crystalline and amorphous phase composition as well as the crystallite particle size. According to XRD and XANES analysis, only the two pure oxide samples and one of the composite samples with a composition TiO2:ZrO2 = 10:1, crystallized. Both titania containing powders, the pure TiO2 and the TiO2:ZrO2 = 10:1 composite, were found to crystallize in the anatase structure. ZrO2 was found to stay amorphous in the composites but crystalline in the pure oxide. In the crystallized composite TiO2:ZrO2 = 10:1 sample, the concentration of the amorphous phase remains larger than in pure TiO2 samples, but the crystallite size was found to be nearly constant with increasing annealing temperature in contrast to the increasing particle size of pure TiO2-samples. Pure TiO2 precipitates are amorphous directly after preparation, however they crystallize after 6 month storage at ambient conditions by aging. Such an aging was not observed for the TiO2:ZrO2 composites.