Effect of aliovalent dopants on the kinetics of spinodal decomposition in rutile-type TiO2-VO2

The effects of aliovalent dopants on the kinetics of spinodal decomposition in a rutile-type TiO2-VO2 system were studied by means of x-ray diffraction and transmission electron microscopy. In this study, as-prepared polycrystalline samples were annealed at 673 k inside the spinodal. For undoped samples, phase decomposition occurred along the [001] direction, and a lamellar structure formed on the nanometer length scale. The phase decomposition kinetics in this system were sensitive to the type of aliovalent dopant; the decomposition rate in a sample doped with Al2O3 was more than one order of magnitude higher than a sample doped with Nb2O5. These observations could be explained on the basis of the premise that cation interstitial mobility is greater than cation vacancy mobility. The obtained results are consistent with those for a TiO2-SnO2 system, indicating that phase separation in both rutile-type oxide systems can be interpreted through a common framework.