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Examination of Synthetic Murataite Structure Using Data of Mossbauer Spectroscopy

Published online by Cambridge University Press:  01 February 2011

Vadim S. Urusov ,
Vyacheslav S. Rusakov ,
Sergey V. Yudintsev  and
Sergey V. Stefanovsky
Vadim S. Urusov
Affiliation:
Moscow State University, Vorob'evy Gory, 119992 Moscow, Russia
Vyacheslav S. Rusakov
Affiliation:
Moscow State University, Vorob'evy Gory, 119992 Moscow, Russia
Sergey V. Yudintsev
Affiliation:
Institute of Geology of Ore Deposits, Staromonetny 35, 119017 Moscow, Russia
Sergey V. Stefanovsky
Affiliation:
SIA “RADON”, 7-th Rostovsky 2/14, 119121 Moscow, Russia
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Abstract

Murataite-based ceramics were recently suggested as promising matrices for immobilization of rare earths and actinides from high-level waste (HLW). Nevertheless, the crystal-chemical formula of the phase has not been accurately determined yet. We have examined structural features of murataite with Mössbauer spectroscopy. Initial batches were prepared from CaO, Al2O3, Fe2O3, MnO2, ZrO2, TiO2, ZrO2, and UO2. Mixtures were melted in platinum crucibles in a resistive furnace in air at 1450°C for 1 h followed by cooling to 1000°C at the rate of 10°C/min. and final cooling down with the furnace switched-off. Study with XRD, SEM, and TEM showed the samples are composed of two co-existing murataite-type phases with five- and eight-fold elementary fluorite cells. To investigate the valence and structural position of iron ions, Mössbauer spectroscopy on 7Fe nuclei in geometry “on absorption” was used. The data obtained let us conclude that in both murataite varieties trivalent iron is distributed almost statistically (3:1) between B octahedra and C five-vertex polyhedra, while tetrahedral sites T are probably not populated. Taking into account these suggestions, the idealized crystal chemical formula of synthetic murataites can be simplified to A3[8]B6[6]C2[5]O22-x/2. Recalculation of chemical analyses to atomic numbers results in the conclusion that average cation valence for murataites is 3.33. Then, calculation for the generalized formula M11O22-x/2 (M=A,B,C) gives a value x/2 = 3.7, i.e., the number of O atoms in the formula is 22–3.7 = 18.3. Final conclusions on the murataite formulae have to be verified by direct structural research on a single crystal.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 807: Symposium Scientific Basis for Nuclear Waste Management XXVII , 2003 , 243
Copyright
Copyright © Materials Research Society 2004

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References

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