TEMPERATURE EFFECTS ON THE SIZE OF ANATASE CRYSTALLITES IN MO-TIO2 AND W-TIO2 POWDERS

The substitution effects of Ti by Mo and W ions on the stability of an atase in commercially available TiO2 powders have been studied by X-ra y diffraction, transmission electron microscopy, and surface area meas urements in the 300-1000 K temperature range. The powder containing W shows smaller microstrains compared to those of pure anatase phase and those containing Mo. The stabilization effect of vacancies in the ana tase phase is discussed and the anatase to rutile transformation cause d by annealing is proposed to be related to the disappearance of Ti3ions in the anatase structure. Finally, a possible redox mechanism Ti3 + double left right arrow Ti4+ + e(-) is proposed to play a fundamenta l role in the catalytic and sensor properties of this material.