Initial stages of the transformation of single-crystal anatase particles during high-energy ball milling

The initial steps of the phase transformation of anatase by high-energy ball milling have been followed as a function of milling time by X-ray diffraction and transmission electron microscopy (TEM). The metastable TiO2 II phase appears after several minutes of grinding. The anatase-TiO2 II transformation occurs without particle fracture. TEM shows the simultaneous strain hardening of anatase particle cores and the formation of TiO2 II crystallites at the surface of anatase particles. The TiO2 II crystallites have an average diameter of about 10 nm. The possible mechanisms of the transformation are commented upon.