Structural characterization of SiO2 and Al2O3 zener-pinned nanocrystalline TiO2 by NMR, XRD and electron microscopy

Nanocrystalline TiO2 samples were prepared using sol-gel techniques in a pure form and also Zener pinned with either silica or alumina to reduce the growth of the crystallites during the annealing process and to stabilize the anatase phase at high temperatures. These samples were studied using O-17, Al-27, and Si-29 nuclear magnetic resonance (NMR), X-ray diffraction (XRD), and electron microscopy. The silica pinning phase was found to successfully restrict nanocrystal growth as well as stabilize the anatase phase at temperatures up to 800 degrees C. The alumina phase had less of a pinning effect, and it reacted with the TiO2 to form tialite. O-17 NMR relaxation time measurements on enriched samples showed that the presence of the pinning phases also reduced the activation energy for the oxygen ion diffusion mechanism.