Charge compensation mechanisms for aliovalent impurities in perovskite and zirconolite

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dc.contributor.authorVance, ERen_AU
dc.contributor.authorDay, RAen_AU
dc.contributor.authorBegg, BDen_AU
dc.contributor.authorBlackford, MGen_AU
dc.date.accessioned2022-08-09T05:58:54Zen_AU
dc.date.available2022-08-09T05:58:54Zen_AU
dc.date.issued1994-02-10en_AU
dc.date.statistics2022-04-07en_AU
dc.description.abstractAs part of the chemical design of Synroc-type ceramics for the immobilisation of different high-level radioactive wastes from nuclear fuel reprocessing, it is necessary to understand the various possible charge compensation mechanisms which occur when up to tens of atomic percent of rare earths and actinides are incorporated in solid solution in perovskite (CaTiO3) and zirconolite (CaZrTi2O7). In particular the solid solution of Gd in the Ca site of perovskite and the incorporation of Nd, Ce, U, Np and Pu in the Ca and Zr sites of zirconolite have been studied by XRD, SEM, TEM, and XANES. The essential conclusions are that in formulations where charge compensating ions are made available, then this is the preferred mechanism for incorporation of these cations in Ca and Zr sites. However in formulations where such compensators are not made available, it is possible for charge compensation to take place via significant abundances of cation vacancies, or by the appearance of unexpected valence states stabilised by crystal-chemical forces. An example of the latter is the probable stabilisation of Ti3+ in Ti sites, and of trivalent Ce and actinides in Ca and Zr sites, even under quite oxidising conditions. A complication in these studies is the effect of prevailing or inherited redox conditions. Redox conditions influence phase abundances and compositions as they control the valencies of cations capable of more than one oxidation state. There is also an indication that reducing conditions can promote oxygen site deficiencies in some formulations. Other complicating factors relate to sample fabrication, arising from the need to make extremely chemically uniform phases having the desired composition. This requires prolonged heating at high temperatures to achieve complete solid-state reaction that may result in selective losses due to volatilisation. Incipient melting due to localised eutectic formation and the apparently straightforward task of efficient stoichiometric mixing on a 1 to 10 um scale are other problems which have had to be overcome in sample fabrication.en_AU
dc.identifier.citationVance, E. R., Day, R. A., Begg, B. D., & Blackford, M. G. (1994). Charge compensation mechanisms for aliovalent impurities in perovskite and zirconolite. Paper presented to the 18th Annual Condensed Matter Physics Meeting, Charles Sturt University, Riverina, Wagga, Wagga, NSW, 9-11 February 1994.en_AU
dc.identifier.conferenceenddate11 February 1994en_AU
dc.identifier.conferencename18th Annual Condensed Matter Physics Meetingen_AU
dc.identifier.conferenceplaceWagga Wagga, NSWen_AU
dc.identifier.conferencestartdate9 February 1994en_AU
dc.identifier.otherTP73en_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/13494en_AU
dc.language.isoenen_AU
dc.publisherAustralian and New Zealand Institutes of Physicsen_AU
dc.subjectCharge statesen_AU
dc.subjectValenceen_AU
dc.subjectCrystal structureen_AU
dc.subjectImpuritiesen_AU
dc.subjectPerovskiteen_AU
dc.subjectSolid solutionsen_AU
dc.subjectStructural chemical analysisen_AU
dc.subjectSynthetic rocksen_AU
dc.subjectVacanciesen_AU
dc.subjectZirconoliteen_AU
dc.titleCharge compensation mechanisms for aliovalent impurities in perovskite and zirconoliteen_AU
dc.typeConference Posteren_AU
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