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Structural Effect of Pu Substitutions on the Zr-Site in Zirconolite

Published online by Cambridge University Press:  21 March 2011

B.D. Begg ,
R.A. Day  and
A. Brownscombe
B.D. Begg
Affiliation:
Materials Division, ANSTO, PMB 1, Menai, NSW, 2234, Australia. Email: [email protected]
R.A. Day
Affiliation:
Materials Division, ANSTO, PMB 1, Menai, NSW, 2234, Australia. Email: [email protected]
A. Brownscombe
Affiliation:
Materials Division, ANSTO, PMB 1, Menai, NSW, 2234, Australia. Email: [email protected]
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Abstract

As the level of Pu4+ substituted on the Zr-site in CaZr1-xPuxTi2O7 zirconolite increased, from x=0.1 to 0.6, a series of structural transitions occurred from zirconolite-2M to zirconolite-4M and subsequently from zirconolite-4M to pyrochlore. The solid-solution limit for Pu4+ substituted on the Zr-site in zirconolite-2M was ~ 0.15 formula units. Zirconolite-4M was only stable over a narrow compositional range, centered about CaZr0.59Pu0.41Ti2O7, whilst the pyrochlore structure was stabilized with CaZr0.4Pu0.6Ti2O7 stoichiometry. The stability of the zirconolite polytypes is therefore sensitive to the average effective ionic size of the ions occupying the seven-coordinated Zr-site. The reduction in Pu from Pu4+ to Pu3+ destabilized the zirconolite-4M, producing a mixture of perovskite and possibly zirconolite-3T. The CaZr0.4Pu0.6Ti2O7 pyrochlore was also predominantly transformed to perovskite as a result of this reduction of Pu.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 663: Symposium – Scientific Basis for Nuclear Waste management XXIV , 2000 , 259
Copyright
Copyright © Materials Research Society 2001

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References

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