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Enthalpies of Formation of Gd2(Ti2-xZrx)O7 Pyrochlores

Published online by Cambridge University Press:  21 March 2011

K.B. Helean ,
B.D. Begg ,
A. Navrotsky ,
B. Ebbinghaus ,
W.J. Weber  and
R.C. Ewing
K.B. Helean
Affiliation:
Thermochemistry Facility, Department of Chemical Engineering and Materials Science, The University of California at Davis, Davis, CA 95616, U.S.A.
B.D. Begg
Affiliation:
Materials Division, Australian Nuclear Science and Technology Organization, PMB 1, Menai, NSW 2234, Australia
A. Navrotsky
Affiliation:
Thermochemistry Facility, Department of Chemical Engineering and Materials Science, The University of California at Davis, Davis, CA 95616, U.S.A.
B. Ebbinghaus
Affiliation:
Lawrence Livermore National Laboratory, Livermore, CA 94550, U.S.A.
W.J. Weber
Affiliation:
Pacific Northwest National Laboratory, Richland, WA 99352, U.S.A.
R.C. Ewing
Affiliation:
Department of Nuclear Engineering and Radiological Sciences, The University of Michigan, Ann Arbor, MI 48109, U.S.A.
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Abstract

A calorimetric investigation of the enthalpies of formation of Gd2(Ti2-xZrx)O7, where 0≤ × ≤ 2 is underway. All samples exhibit pyrochlore (Fd3m) peaks in their XRD patterns. However, where x=2 significant local disorder is observed in the Raman spectra. Preliminary data for the enthalpies of formation from the oxides in kJ/mol are: x=0, ΔHf = -113.4±2.7; x=0.5, ΔHf = -94.0±3.0; x=1.0, ΔHf = -74.2±4.9; x=1.5, ΔHf = -64.5±2.0; x=2, ΔHf = -52.2±4.8. Two additional samples, Gd1.80Zr2.15O7.00 (pyrochlore) and Gd2.15Zr1.87O7.00 (fluorite), were also studied. Their enthalpies of formation from the oxides in kJ/mole are -50.9±3.3 and -46.4±3.4 respectively. Replacing Ti with Zr, i.e. when x=2, destabilizes the pyrochlore in enthalpy by approximately 60 kJ/mol. The ΔHmix for the Gd2(Ti2-xZrx)O7 solid-solution series is positive and can be described by a regular solution formalism with an estimated interaction parameter, ŝ = +20 kJ/mol. The results of this study suggest that the pyrochlore to fluorite transition enthalpy in Gd2Zr2O7 is small, of the order of the configurational entropy contribution due to cation disorder at the transition temperature, TΔSconf. ≍ 10 kJ/mol.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 663: Symposium – Scientific Basis for Nuclear Waste management XXIV , 2000 , 691
Copyright
Copyright © Materials Research Society 2001

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References

REFERENCES

1.Record of Decision for the Storage and Disposition of Weapons-usable Fissile Materials, Final Programmatic Environmental Impact Statement, January 14, 1997, U.S. Department of Energy, Washington, D.C. 1997.Google Scholar
2. Ringwood, A.E. (1978) Safe Disposal of High Level Nulcear Reactor Wastes: A New Strategy, ANU Canberra, Australia.Google Scholar
3. Ringwood, A.E., Kessen, S.E., Reeve, K.D., Levins, D.M. and Ramm, E.J., in Radioactive Waste Forms for the Future, Eds. Lutze, W. and Ewing, R.C., Elsevier, North-Holland, Amsterdam, Netherlands, pp 233–334 (1988).Google Scholar
4. Weber, W.J., Wald, J.W. and Matzke, Hj. (1985) Self-radiation damage in Cm-doped Gd2Ti2O7, Materials Letters, 3, 173-180.Google Scholar
5. Weber, W.J., Wald, J.W. and Matzke, Hj. (1986) Effects of self-radiation damage in Cm-doped Gd2Ti2O7 and CaZrTi2O7, Journal of Nuclear Materials, 138, 196–209.Google Scholar
6. Weber, W.J. and Hess, N.J. (1993) Ion beam modification of Gd2Ti2O7, NuclearInstrumentation and Methods, B80/81, 1245–1251.Google Scholar
7. Wang, S.X., Wang, L.M., Ewing, R.C. and Kutty, K.V. Govidan (2000) Ion irradiation of rare-earth and yttrium-titanate pyrochlores, Nucl. Instrum. Methods Physics Res. B., 169, 135–140.Google Scholar
8. Wang, S.X., Begg, B.D., Wang, L.M., Ewing, R.C., Weber, W.J. and Kutty, K.V. Govidan (1999) Journal of Materials Research, 14(12), 4470–4473.Google Scholar
9. Wang, S.X., Wang, L.M., Ewing, R.C. and Kutty, K.V. Govidan (1999) Microstructural Processes in Irradiated Materials, edited by Zinkle, S.J. Lucas, G.E., Ewing, R.C. and Williams, J.S., Materials Research Society Symposium Proceedings, vol.540, 355–360.Google Scholar
10. Begg, B. D., Hess, N.J., McCready, D.E., Thevuthasan, S. and Weber, W.J. (2000) Heavy-ion irradiation effects in (Gd2(Ti2-xZrx)O7 pyrochlores, American Ceramic Society Symposium Proceedings, 107, 553–560.Google Scholar
11. Sickafus, K.E., Minervini, L., Grimes, R.W., Valdez, J.A., Ishimaru, M., Li, F., McClellan, K.J. and Hartman, T. (2000) Radiation tolerance of complex oxides, Science, 289, 748–751.Google Scholar
12. Weber, W.J. and Ewing, R.C. (2000) Plutonium immobilization and radiation effects, Science, 289(5487), 2051.Google Scholar
13. Navrotsky, A. (1997) Progress and new directions in high temperature calorimetry revisited, Phys. Chem. Minerals, 24, 222–241.Google Scholar
14. McHale, J.M., Kowach, G.R., Navrotsky, A. and DiSalvo, F.J. (1996) Thermochemistry of metal nitrides in the Ca/Zn/N system, Chem. Eur. J. 2, 1514.Google Scholar
15. Handbook on the physics and chemistry of rare earths, vol. 16, Eds. Gschneidner, K.A. and Eyring, L., Elsevier, North-Holland, Amsterdam, Netherlands, pp 589 (1993).Google Scholar
16. Robie, R.A., Hemingway, B.S., Thermodynamic Properties of Minerals and Related Substances at 298.15 and 1 Bar (105 Pascals) Pressure and at Higher Temperatures (U.S. Government Printing Office: Washington, D.C. 1995).Google Scholar
17. Molodetsky, I. (1999) Energetics of Zirconia Stabilized by Cation and Nitrogen Substitution, Ph.D. Dissertation, Princeton University.Google Scholar