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Powder diffraction studies of mixed titanium zirconium phosphates

Victoria A. Burnell ,  Jennifer E. Readman ,  Joseph A. Hriljac 

School of Chemistry, University of Birmingham, Edgbaston, Birmingham B152TT, United Kingdom

Abstract
Issues relating to the removal and storage of radionuclides are important as they are a key component for the use of nuclear power to generate energy and because of the threat of “dirty bombs” by terrorists.  Therefore, research into materials that can sequester cations like Sr2+ from water must continue and consequently there has been a renewed interest in layered zirconium phosphates due to their ion-exchange abilities [1, 2]. It has been suggested that the ion-selectivity of zirconium phosphate could be altered by the presence of titanium [3]. Only two previous literature reports of mixed titanium zirconium phosphates exist, but these were poorly crystalline materials [3, 4] so little structural characterisation was undertaken. Here we present the synthesis and structure of a series of crystalline layered mixed titanium zirconium phosphates ranging from α-zirconium phosphate to α-titanium phosphate, and in situ powder XRD studies of their thermal decomposition.

Both traditional Rietveld methods and pair distribution function analysis (PDF) of powder X-ray diffraction data [5] are being used to characterise the structures. It was found that at low doping levels the materials are structurally similar to the end member that they are compositionally closest to, and no ordering of the titanium or zirconium was found. However, at higher substitution levels PDF methods suggest the presence of two closely related phases, thus implying that there are solubility limits for both series end members. PDF studies are currently being used to refine the local and long range ordering enabling a comparison of the Ti:Zr ratio within these areas to the average structure.

The exchanged phases were thermally decomposed and monitored with variable temperature XRD.

Figure 1: PDF results for the series ZrxTi1-x(HPO4)2.H2O where x = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1. The peaks represent the atomic distances within the structures.

References:
1) Clearfield,A., Costantino,U., Comprehensive Supramolecular Chemistry 7, 107, (1996).
2) Alberti,G., Acc. Chem. Res., 11, 163, (1978).
3) Clearfield, A., Frianeza, T. N., J. Inorg. Nucl. Chem. 40, 1925, (1978).
4) Jingnasa, A., Rakesh, T., Uma, T., J. Chem. Sci. 118, 185, (2006).
5) Billinge, S. J. L., Kanatzidis, M. G., Chem. Commun. 749, (2004).


 

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Related papers
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  2. Pair distribution studies of ion-exchanged α-zirconium phosphate
  3. In-situ high-pressure powder diffraction studies of layered metal phosphates

Presentation: Poster at 11th European Powder Diffraction Conference, Poster session, by Victoria A. Burnell
See On-line Journal of 11th European Powder Diffraction Conference

Submitted: 2008-04-28 17:11
Revised:   2009-06-07 00:48