A Study of PbTiO_3 Crystallization in Pure and Composite Nanopowders Prepared by the Sol-Gel Technique

摘要

In this investigation the crystallization of PbTiO_3 upon annealing of pure nanopowders and PbTiO_3-SiO_2 (1:1 v/v) nanocomposite powders prepared by the sol-gel technique was studied. Using X-ray diffraction phase analysis, the start of PbTiO_3 crystallization in pure PbTiO_3 powders was detected at 400 deg C. Distinct crystallization of PbTiO_3 in PbTiO_3-SiO_2 nanocomposites starts at 700 degC, whereas SiO_2 remains amorphous. There are indications that an interface interaction between the PbTiO_3 and the SiO_2 phase plays a important role in hindering the crystallization of PbTiO_3. The particle size (size of coherently scattering regions) was estimated from the broadening of the X-ray diffraction line profiles. The average size of PbTiO_3 nanocrystallites increases with temperature and time of annealing, the influence of temperature being more significant than that of the annealing time. Differential scanning calorimetry confirmed the results of the X-ray diffraction with respect to the start of the crystallization. Laser beam scattering and scanning electron microscopy provided the statistical distribution of the grain size and the morphology of hte powder grains, showing that each grain of the powders contains several nanocrystallites (coherently scattering regions).