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Analysis of Coordination Polyhedra Symmetry in Pyrochlore and Zirconolite Structures

Published online by Cambridge University Press:  10 February 2011

A. Y. Troole  and
S. V. Stefanovsky
A. Y. Troole
Affiliation:
SIA "Radon", 7th Rostovskii per. 2/14, Moscow 119121 Russia, itbstef@cityline.ru
S. V. Stefanovsky
Affiliation:
SIA "Radon", 7th Rostovskii per. 2/14, Moscow 119121 Russia, itbstef@cityline.ru
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Abstract

Zirconolite and pyrochlore are considered as promising host phases for high level waste (HLW). However, correct information on substitution mechanisms, forms of dopants incorporation in their structures and distortions in coordination polyhedra is presently unavailable. To clarify these points we use the electron paramagnetic resonance (EPR). Pyrochlore and three of zirconolite polytypes: zirconolite-2M, zirconolite-3T, and zirconolite-30 are considered. Pyrochlore is the “parent” structure for zirconolite since any zirconolite variety is produced by means of distortion of the initial pyrochlore structure. Space groups of pyrochlore and basic polymorphous zirconolite varieties found from XRD and TEM data, as well as interatomic distances and angles, were taken from reference data. This allows the determination of the most probable sites for impurities, substitution mechanisms, and local symmetry of coordination polyhedra (initial). Ions chosen for EPR were Gd (III) as an analog of trivalent rare earth and actinide elements which are also occurred in HLW and Fe (III) as a typical corrosion product which occurs in all HLW. For Gd (III) a strong ligand field approximation is suggested, theoretical computation using perturbation theory in this approximation has been carried out. All the non-diagonal members plus magnetic field were chosen as perturbation and formulae for transition frequencies, estimations of fine structure and g-factors parameters in the given approximation have been obtained.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 556: Symposium QQ – Scientific Basis for Nuclear Waste Management XXII , 1999 , 35
Copyright
Copyright © Materials Research Society 1999

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