STRUCTURAL-CHANGES OF TITANIUM-OXIDE INDUCED BY CHROMIUM ADDITION AS DETERMINED BY AN X-RAY-DIFFRACTION STUDY

An X-ray diffraction study has been carried out on a series of polycrystalline TiO2 (anatase) catalysts containing Cr(III) at different atomic concentrations (0.2-5.0 at,%), prepared by a coprecipitation method, Analysis of the variation of the unit cell parameters of chromium-doped anatase with respect to pure anatase has allowed us to estimate the solubility limit for the system at around 1.4 at.%. There is no evidence for the existence of a separate crystalline chromium oxide phase. Temperature effects on the cell parameter and on the anatase-rutile transformation rate were also analyzed, An increase in temperature produced release of the chromium from the solid solution. At the same time, an acceleration in the rate of the anatase-to-rutile phase transition was observed. (C) 1995 Academic Press, Inc.