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1124-Q10-08

In Situ Radiation Damage Studies of Ca3Zr2FeAlSiO12 and Ca3Hf2FeAlSiO12 Karl R. Whittle1, Mark G. Blackford1, Gregory R. Lumpkin1, Katherine L. Smith1, and Nestor J. Zaluzec2 1 Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, PMB1, Menai, NSW 2234, Australia 2 Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA ABSTRACT Garnets, A3B2C3O12, are considered to be potential host phases for the immobilization of high-level nuclear waste as they can accommodate a number of elements of interest, including Zr, Ti and Fe. The naturally occurring garnet, kimzeyite, Ca3(Zr,Ti)2(Si,Al,Fe)3O12, can contain ~30wt% Zr. An understanding of the radiation tolerance of these materials is crucial to their potential use in nuclear waste immobilization. In this study two synthetic analogues of kimzeyite of composition Ca3Zr2FeAlSiO12 and Ca3Hf2FeAlSiO12 were monitored in situ during irradiation with 1.0 MeV Kr ions using the intermediate voltage electron microscope-Tandem User Facility (IVEM) at Argonne National Laboratory. The structure of these materials was previously determined by neutron diffraction and 57Fe Mössbauer spectroscopy. Ca3Zr2FeAlSiO12 and Ca3Hf2FeAlSiO12 have very similar structural properties with cubic Ia3d symmetry, the only significant difference being the presence of Zr and Hf, respectively, on the 6 coordinated B sites. INTRODUCTION Naturally occurring garnets are found with a large range of elemental compositions with the cations located across more than one site in the lattice, e.g., schorlomite. Garnets can be prepared containing U, Th and lanthanide elements; as such they make ideal candidates for the long-term storage of actinide waste. Current research in new materials for actinide waste tend to contain titanium and zirconium, this was originally due to the existence of compatible Ti phases for high-level waste, e.g., hollandite, pyrochlore and zirconolite. Zirconium has been added in recent research to enhance the stability to radiation damage. In nature there are two garnets that make ideal candidates for waste form research that have high levels of Ti4+ (schorlomite) or Zr4+ (kimzeyite), with kimzeyite and simplified analogues being the focus of this work. A schematic of the garnet structure is shown in Figure 1. Kimzeyite Ca3(Zr,Ti)2(Si,Al,Fe)3O12 [1-5] was originally reported in 1961 for a sample from Magnet Cove in Arkansas, it is a naturally occurring garnet that contains high levels of Zr (~30wt% ZrO2). There have been two subsequent analyses published based on samples from the Aeolian Islands, and the Sabatini Volcanic district, both in Italy. All three analyses give similar values for elemental composition and crystal parameters. As these garnets are naturally occurring with good long-term stability, they are ideal to study as potential storage media for radioactive nuclear waste. In this work we have irradiated Ca3Zr2FeAlSiO12 and Ca3Hf2FeAlSiO12, which have previously been studied to determine the cation location with