Structural transformative behaviour in barium thorium oxides: a neutron and synchrotron x-ray diffraction study
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Date
2016-11-30
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Australian Institute of Nuclear Science and Engineering
Abstract
The increasing interest in nuclear energy, as a response to demands for a transition to non-fossil fuel energy sources, has reinvigorated attempts to explore a thorium fuel cycle. Thorium is seen as a more attractive option to uranium as a nuclear fuel, due to its enhanced proliferation resistance and reduced transuranic generation. Thorium reactors face several challenges particularly related to the large paucity of information of fuel fission by product material phases. A pertinent structure in this regard is BaThO3, due its potential to host the fission daughter Ba-137m. The radioactivity of thorium coupled with the unusual decomposition behaviour of BaThO3, has prevented detailed analysis of the material. The present study has utilized a combination of neutron and synchrotron x-ray diffraction in order to establish the structure of BaThO_3 and elucidate its high temperature structural behaviour. Our results indicate BaThO_3 undergoes a reversible second order continuous phasetransformation at 975 K from the space group Pbnm to Imma. Neutron and synchrotron Xrays were key to this, successfully resolving the characteristic superlattice X-point and Mpoint reflections present in Pbnm and absent in Imma. Considering the decomposition behaviour of BaThO_3 attempts were made to include Th(IV) partially on the B site of otherABO_3 perovskites including BaZrO_3 and SrZrO_3 through the formation of appropriate solid solutions. This resulted in maximum Th solubilities of less than 10 %. Surprisingly greater solubilities are known for Th(IV) on the A site of in layered perovskites such as Na_2_/_3Th_1_/_3TiO_3. The ability of Th to occupy the perovskite A-site is in contrast to that what is typically observed for uranium and other nuclear fuel relevant perovskites.
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Keywords
Barium 137, Crystal lattices, Crystallography, Neutron diffraction, Perovskites, Particle structure, Nuclear fuels, Particle structure, Perovskites, Synchrotron radiation
Citation
Murphy, G. L., Kennedy, B. J., Avdeev, M., & Zhang, Z. (2016). Structural transformative behaviour in barium thorium oxides: a neutron and synchrotron x-ray diffraction study. Paper presented at 13th AINSE-ANBUG Neutron Scattering Symposium (AANSS 2016); Sydney, NSW, Australia, 29-30 November 2016.