Growth and Optical Properties of Rectangular Hollow Tube TiO2 Crystals with Rutile-Type Structure

Rectangular hollow tube crystals of the rutile-type TiO2 have been successfully grown in supercritical water at about 2 GPa for the first time using a diamond-anvil cell combined with the infrared laser heating system. The scanning electron microscope (SEM) and transmission electron microscope (TEM) observations indicate that they are grown along the [001] direction in a few tens of micrometer lengths. It is also found that they are surrounded by the {110} face with its wall thickness of ∼200 nm. Details of the morphology, optical property, and growth mechanism of the obtained crystals are discussed.