Raman spectroscopy of ball-milled TiO2

Raman spectroscopy was applied to study structural and dimensional changes during high-energy ball milling of TiO2 anatase. Milling was performed for up to 10 h using two different sets of grinding tools (wolfram carbide (WC) and agate), The diminution of the TiO2 particle to nanometric size was mon itoring by low-frequency Raman spectroscopy. The nanometric sizes were conf irmed by transmission electron microscopy (TEM). After short milling time by WC the bands of high-pressure TiO2 II phase (al pha -PbO2 structure) were detected in Raman spectrum. Prolonged milling tim e was needed for transformation to rutil. When milling was performed by aga te, the time necessary for both phase transitions was longer, presumably be cause of lower ball-to-powder weight ratio. The low-frequency Raman band of the prolonged milled samples was broad, whi ch suggests the wide dispersion in nanoparticle dimensions. The position of the low-frequency band in longer-milled samples indicated dimensions small er than 20 nm, since the diameter of the particle is inversely proportional to the low-frequency mode of the spherical particles. These results were i n agreement with the TEM results. (C) 2001 Elsevier Science B.V. All rights reserved.