Hostname: page-component-848d4c4894-75dct Total loading time: 0 Render date: 2024-05-17T15:22:24.945Z Has data issue: false hasContentIssue false
  • English
  • Français

Structures and Stabilities of Trivalent and Tetravalent Rare Earth Ions in Sevenfold Andeightfold Coordination in Fluorite-Related Complex Oxides

Published online by Cambridge University Press:  25 February 2011

Lester R. Morss
Lester R. Morss*
Affiliation:
Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
Get access

Abstract

This paper reports the preparation and characterization of a series of oxides containing3+ or 4+ lanthanide (M = Ce, Pr, or Tb) ions, with different ionic sizes and varying M4+/M3+ reduction potentials, in nearly cubic coordination. The objective of the study was to demonstrate how oxidation-reduction characteristics and ionic-size trends explain the properties of these oxides and to compare the oxidation-reduction stability of M3+ and M4+ lanthanide ions in high (CN 7 or 8) coordination in fluorite-related oxides versus low (CN 6) coordination in perovskite oxies. Efficient preparative methods are reported, as well as powder diffraction and thermogravimetric measurements for oxides CaMTi2O7-x and CaMZr2O7-x. These oxides were characterized by X-ray powder diffraction and by thermogravimetric analysis. CaCeTi2O7 is a pyrochlore, a = 10.142(4) Å with Ce4+ much more easily reducible than in the perovskite BaCeO3. By contrast, a preparation with the stoichiometry “CaPrTi2O7-x” is a two-phase mixture of perovskite CaTiO3 and a presumably Pr3+-rich pyrochlore Pr2Ti2O7(?). CaTbTi2O7-x appears to be a Tb3+ pyrochlore, a = 10.149(2) Å. CaCeZr2O7 is a pyrochlore, a = 10.524(1) sÅ. A preparation of “CaPrZr2O7-x” also appeared to yield a two-phase mixture, perovskite CaZrO3 and pyrochlore Pr2Zr2O7. In this paper, the structures, f-element ion sites, and M(IV)- MM1I stability trends in the CaMTi2O7-x and CaMZr2O7-x oxides are compared with the structural and stability trends in the perovskites BaMO3 which have M4+ ions in sixfold (tilted octahedra) coordination.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 257: Symposium – Scientific Basis for Nuclear Waste Management XV , 1991 , 275
Copyright
Copyright © Materials Research Society 1992

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

REFERENCES

1. Morss, L. R., in Standard Potentials in Aqueous Solution, edited by Bard, A. J., Parsons, R., and Jordan, J., Marcel Dekker, New York, 1985, ch 20; L. Martinot and J. Fuger, ibid., ch. 21.Google Scholar
2. Katz, J. J., Seaborg, G. T., and Morss, L. R., Morss, L. R., chapter 14 in The Chemistry of the Actinide Elements, edited by Katz, J. J., Seaborg, G. T., and Morss, L. R. (Chapman & Hall, 1986).Google Scholar
3. Shannon, R. D., Acta Crystallogr. A32, 751 (1976)CrossRefGoogle Scholar
4. Muromura, T., in The Geological Disposal of High Level Radioactive Wastes. Brookins, D. G., ed., Theophrastus Publications, Athens, 1987, pp. 265–289.Google Scholar
5. Matzke, H.-J., Ray, I. L. F., Seatonberry, B. W., Thiele, H., Trisoglio, C., Walker, C. T., and White, T. J., J. Am. Ceram. Soc. 73, 370 (1990).CrossRefGoogle Scholar
6. Weber, W. J., Wald, J. W., and Matzke, H.-J., in Scientific Basis for Nuclear Waste Management VIII, edited by Jantzen, C. M., Stone, J. A., and Ewing, R. C., Materials Research Society, Pittsburgh, PA, 1985, pp. 679–686.Google Scholar
7. Lumpkin, G. R. and Ewing, R. C., Phys. Chem. Minerals 16, (1988) 2.CrossRefGoogle Scholar
8. Subramanian, M. A., Aravamudan, G., and Rao, G. V. Subba, Prog. Solid St. Chem. 115, 55 (1983).CrossRefGoogle Scholar
9. Bayliss, P., Mazzi, F., Munno, R., and White, T.J., Mineral. Magazine 53, 565 (1989).CrossRefGoogle Scholar
10. Chakoumakos, B. C. and Ewing, R. C., in Scientific Basis for Nuclear Waste Management VIII, edited by Jantzen, C. M., Stone, J. A., and Ewing, R. C., Materials Research Society, Pittsburgh, PA, 1985, pp. 641–6.Google Scholar
11. McCauley, R. A. and Hummel, F. A., J. Solid State Chem. 33, 99 (1980).CrossRefGoogle Scholar
12. Dickson, F. J., Hawkins, K. D., and White, T. J., Report UM-P-88-1 15 (Australian Nuclear Science and Technology Organisation).Google Scholar
13. Clinard, F. W. Jr., Peterson, D. E., Rohr, D. L., and Hobbs, L. W., J. Nucl. Mater. 126, 245 (1984); unit cell reported as 5.066 A but doubled in Table IV.CrossRefGoogle Scholar
14. Hennings, D. and Mayr, W., J. Solid State Chem. 26, 329 (1978).CrossRefGoogle Scholar
15. Velde, E. G. M. H. van de, Lippens, B. C., Korf, S. J., and Boeijsma, J., Powder Diffraction 5, 229 (1990).CrossRefGoogle Scholar
16. Williams, D. E., Iowa State University Report IS-1052 (1964).Google Scholar