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.