Crystallization of amorphous TiO₂ nanotubes: A real-time synchrotron X-ray scattering study

We studied the crystallization behavior of 5 m-thick amorphous TiO₂ nanotubes for renewable energy applications by performing real-time synchrotron X-ray scattering experiments during annealing in air and vacuum. The TiO₂ nanotubes prepared by anodic oxidation were amorphous at room temperature. The crystallization temperatures of anatase and rutile phases of TiO₂ were lower in vacuum than those in air because of the presence of oxygen vacancies caused by the oxygen deficiency. The crystalline rutile phase was formed through both the crystallization of the amorphous phase at low temperatures and transformation of the anatase phase at high temperatures both in air and vacuum. The rutile phase formed larger crystal domains at a lower crystallization temperature in vacuum when compared to the crystallization behavior in air.