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Title: Nonstoichiometry, amorphicity and microstructural evolution during phase transformations of photocatalytic titania powders
Authors: Lim, S.H.
Ritter, C.
Ping, Y. 
Schreyer, M.
White, T.J.
Keywords: Anatase
Neutron powder diffraction
Phase transformation
Titania - amorphous
X-ray microabsorption
X-ray powder diffraction - multiple wavelength
Issue Date: 2009
Citation: Lim, S.H., Ritter, C., Ping, Y., Schreyer, M., White, T.J. (2009). Nonstoichiometry, amorphicity and microstructural evolution during phase transformations of photocatalytic titania powders. Journal of Applied Crystallography 42 (5) : 917-924. ScholarBank@NUS Repository.
Abstract: The performance of photocatalytic titania powders is regulated, in part, by nonstoichiometry and the proportions of the crystalline and amorphous components. These variables can be quantitatively established by Rietveld analysis of diffraction data when internal standards are used to fix absolutely the crystallochemical parameters during quantitative phase analysis and to correct for mass absorption. Here, fixed-wavelength neutron and multiple-wavelength X-ray powder diffraction are used to assess phase development in alkoxide-derived titania gel as a function of temperature. In this manner, it is shown that the amorphous gel is progressively replaced by anatase for temperatures 773 K, and that during the reconstructive transition to rutile (773-873 K) aperiodicity increases as anatase is broken down to clusters of TiO6 octahedra, with a fraction (10 wt%) of this short-range order persisting to 1273 K. Microabsorption correlates with X-ray energy, leading to systematic aberrations in the Rietveld scale factors connected to microstructural evolution which accompanies phase development during heat treatment. These changes are consistent with encapsulation of anatase and rutile by ubiquitous non-diffracting materials. The appearance of significant quantities of an intervening disordered phase during the dimorph transformation is supportive of recent kinetic models; however, its impact on catalytic activity remains to be determined. © 2009 International Union of Crystallography Printed in Singapore - all rights reserved.
Source Title: Journal of Applied Crystallography
ISSN: 00218898
DOI: 10.1107/S0021889809031021
Appears in Collections:Staff Publications

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