Characterization of nanocrystalline anatase titania: an in situ HTXRD study

Abstract

Nanocrystalline titania was synthesized by the hydrolysis of titanium iso-propoxide using ultrasonication. The powder XRD patterns of the sample were recorded in static air and vacuum using a Philips X-pert Pro diffractometer equipped with a high-temperature attachment (HTK16) from room temperature (298 K) to 1173K and were analyzed by the Rietveld refinement technique. The anatase to rutile phase transformation was observed at 1173K for the data collected in static air. Only 3% of anatase titania transformed to rutile when the experiments were carried out at 1173K in vacuum. The phase transformation from anatase to rutile is accompanied by a continuous increase in the crystallite size of the anatase phase from 9 nm at room temperature to 28 nm at 873K and then to 50 nm at 1173K in air while the process of crystallite growth was suppressed in vacuum. A linear increase in the unit cell parameters ‘a’ and ‘c’, and thus, an overall linear increase in the unit cell volume was observed as a function of temperature in static air as well as vacuum. The lattice and volume thermal expansion coefficients (TEC), αa, αc and αV at 873K are 8.57 × 10−6, 8.71 × 10−6 and 25.91 × 10−6 K−1 in air and 18.01 × 10−6, 14.95 × 10−6 and 51.13 × 10−6 K−1 in vacuum, respectively.