Radiation tolerance of A2Ti2O7 compounds at the cubic-monoclinic boundary

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dc.contributor.authorLumpkin, GRen_AU
dc.contributor.authorHarvey, EJen_AU
dc.contributor.authorSmith, KLen_AU
dc.contributor.authorBlackford, MGen_AU
dc.contributor.authorZaluzec, NJen_AU
dc.date.accessioned2022-11-03T23:40:28Zen_AU
dc.date.available2022-11-03T23:40:28Zen_AU
dc.date.issued2006-10-15en_AU
dc.date.statistics2022-10-11en_AU
dc.description.abstractCeramic waste forms provide attractive alternatives to the direct disposal of spent fuel or the immobilisation of high-level radioactive waste in borosilicate glass. They are particularly suited for the disposal of actinide wastes (e.g., from partitioning strategies, or for excess Pu from defence purposes) and furthermore they exhibit very low dissolution rates in aqueous fluids, making them attractive candidates for certain repository scenarios (e.g., deep disposal). For general background information on these materials, including studies of the crystal chemistry, aqueous durability, and the behaviour of natural analogues in geological systems, readers are referred to references [1-4]. Over the design lifetime of ceramic waste forms, the actinide elements will undergo alpha decay, resulting in damage to the crystalline structure primarily due to alpha recoil collision cascades. In certain materials, this will lead to a crystalline-amorphous transformation accompanied by volume expansion and reduced chemical durability. The performance in aqueous fluids may be compromised by cracking, increased surface area, and decreased thermodynamic stability of the amorphous phase. Consequently, the radiation damage effects have been of particular interest in ceramic waste forms. Detailed reviews of radiation damage effects can be found in references [5-7]. Some aspects of the alpha decay process have been simulated by irradiation with heavy ions under controlled experimental conditions. In this study, we conducted in situ ion irradiation experiments using the IVEM-Tandem Facility at Argonne National Laboratory to determine the radiation response of Gd2Ti2O7 pyrochlore and two monoclinic, layered perovskite-type phases, Nd2Ti2O7 and La2Ti2O7. For each compound, the critical amorphization dose Dc was determined as a function of temperature and used to establish Tc , the critical temperature, above which the compound remains crystalline. Together with previous data for the A2Ti2O7 compounds, our results show a clear reversal in the trend of Tc versus the cation-anion radius ratio rM/rX. Our experimental results are discussed in the general context of the potential factors that control the susceptibility of a given compound to amorphisation, which include aspects of the structure, bonding, and disorder energy. For the A2Ti2O7 compounds we also show that the critical temperature correlates with the electronic structure (e.g., 4f occupancy) of lanthanide cations. This appears to be a unique result in the world of ion irradiation studies, but the story is complicated by the phase transition from pyrochlore to the layered perovskite structure in this system. Our ultimate goal here is to illustrate the need for a detailed understanding of the physical processes of radiation damage and the potential for predictive modelling of waste form performance.en_AU
dc.identifier.citationLumpkin G. R., Harvey E. J., Smith K. L., Blackford M. G., & Zaluzec N. J. (2006). Radiation tolerance of A2Ti2O7 compounds at the cubic-monoclinic boundary. Paper presented at the 15th Pacific Basin Nuclear Conference (PBNC), Sydney, Australia, 15-20 October 2006. Retrieved from: http://www.webetc.info/pnc/2006-Proceedings/pdf/0610015final00228.pdfen_AU
dc.identifier.conferenceenddate20 October 2006en_AU
dc.identifier.conferencename15th Pacific Basin Nuclear Conference (PBNC)en_AU
dc.identifier.conferenceplaceSydney, Australiaen_AU
dc.identifier.conferencestartdate15 October 2006en_AU
dc.identifier.urihttp://www.webetc.info/pnc/2006-Proceedings/pdf/0610015final00228.pdfen_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/13968en_AU
dc.language.isoenen_AU
dc.publisherAustralian Nuclear Associationen_AU
dc.subjectIrradiationen_AU
dc.subjectCeramicsen_AU
dc.subjectWaste formsen_AU
dc.subjectRadioactive wastesen_AU
dc.subjectActinidesen_AU
dc.subjectAlpha decayen_AU
dc.titleRadiation tolerance of A2Ti2O7 compounds at the cubic-monoclinic boundaryen_AU
dc.typeConference Paperen_AU
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