EXAFS analysis of the structural evolution of gel-formed La₂O₃

Abstract

Sol–gel-produced La₂O₃ , derived from the hydrolysis and subsequent calcination of lanthanum isopropoxide, has been investigated by EXAFS of the La L_III edge. The evolution of the local structure through a series of amorphous intermediate states has been modelled by three shells, two lanthanum–oxygen and the other lanthanum–lanthanum. For comparison, well characterised bulk La(OH)₃ , LaO(OH) and La₂O₃ were examined using EXAFS. The sol–gel-prepared oxide was more disordered and had significantly smaller particles than the oxide prepared by calcination of La₂(CO₃)₃ after the same heat treatments. For the gels in the intermediate states, well defined La–O shells are seen but the La–La shells are characterised by large Debye–Waller factors. Comparison of these results with previous ¹⁷O solid-state NMR on a similar set of samples has some significant implications for the sensitivity to disorder of these important atomic-scale probes.

References

1. R. Birringer, H. Hahn, H. Hoefler, J. Karch and H. Gleiter, Defect and Diff usion Forum, 1988, 59, 17.
2. D. C. Koningsberger and R. Prins, X-Ray Absorption, Wiley, London, 1988.
3. S. J. Gurman, in Applications of Synchrotron Radiation, ed. C. R. A. Catlow and G. N. Greaves, Blackie, London, 1993, p. 140; A. V. Chadwick, in Applications of Synchrotron Radiation, ed. C. R. A. Catlow and G. N. Greaves, Blackie, London, 1993, p. 171.
4. K. D. Campbell, H. Zhang and J. H. Lunsford, J. Phys. Chem., 1988, 92, 750.
5. Z. Kalinek and E. E. Wolf, Catal. Lett., 1991, 9, 441.
6. S. J. Milne, R. J. Brook and Y. S. Zhen, Br. Ceram. Proc., 1989, 41, 243.
7. F. Ali, M. E. Smith, S. Steuernagel and H. J. Whitfield, J. Mater. Chem., 1996, 6, 261.
8. P. Malet, M. J. Captian, M. A. Centano, J. A. Odriozola and I. Carrizoa, J. Chem. Soc., Faraday Trans., 1994, 90, 2783.
9. A. V. Chadwick, G. Morrison and R. Rafiuddin, Radiat. Effects Defects Solids, 1995, 134, 91.
10. R. M. Almeida, M. I. Marques and M. C. Goncalves, J. Non-Cryst. Solids., 1994, 168, 144.
11. E. M. Larson, A. J. G. Ellison, F. W. Lytle, A. Navrotsky, R. B. Greegor and J. Wong, J. Non-Cryst. Solids, 1990, 130, 260.
12. S. Benazeth, M. H. Tuiler, A. M. Loireau-Lozac, H. Dexpert, P. Lagarde and J. Flattaut, J. Non-Cryst. Solids, 1989, 110, 89.
13. F. J. Berry, S. Greaves and R. C. Lobo, J. Chem. Soc., Faraday Trans., 1991, 87, 1405.
14. SERC Daresbury Program Library, 1991.
15. N. Binsted, J. W. Campbell, S. J. Gurman and P. C. Stephenson, SERC Daresbury Program Library, 1992.
16. D. J. Illet and M. S. Islam, J. Chem. Soc., Faraday Trans., 1993, 89, 3833.
17. W. H. Zaichariasen, Acta Crystallogr., 1948, 1, 265.
18. G. W. Beall, W. O. Milligan and H. A. Wolcott, J. Inorg. Nucl. Chem., 1977, 39, 65.
19. P. V. Klevsov and L. P. Sheina, Akad. Nauk SSSR Neorg. Mater., 1965, 1, 2219.
20. R. Nitsche, M. Winterer, M. Croft and H. Hahn, Nucl. Instrum. Methods Phys. Res. Sect. B, 1995, 97, 127.
21. G. J. Baker, G. N. Greaves, M. Surman and M. Oversluizen, Nuclear Instrum. Methods Phys. Res., Sect. B, 1995, 97, 375.