Browsing by Author "Clements, R"

Now showing 1 - 4 of 4
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    Does local disorder occur in the pyrochlore zirconates?
    (American Chemical Socity, 2012-12-17) Blanchard, PER; Clements, R; Kennedy, BJ; Ling, CD; Reynolds, EM; Avdeev, M; Stampfl, APJ; Zhang, Z; Jang, LY
    The zirconates Ln2Zr2O7 (Ln = lanthanoid) have been studied using a combination of Zr L-edge X-ray absorption near edge structure (XANES) and synchrotron X-ray and neutron powder diffraction methods. These studies demonstrate that as the size of the lanthanoid cation decreases, the local structure evolves smoothly from the ideal pyrochlore toward the defect fluorite rather than undergoing an abrupt transformation. The Zr L-edge spectrum is found to be extremely sensitive to changes in the local coordination environment and demonstrates an increase in local disorder across the pyrochlore oxides. The sensitivity of the XANES measurements enables us to identify the progressive nature of the transition that could not be detected using bulk diffraction techniques. © 2012, American Chemical Society.
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    The fermi surface of Cu3Mn {100} and spin-glass magnetism
    (Australian Institute of Physics, 2009-02-06) Clements, R
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    The fluorite-pyrochlore transformation of Ho2-yNdyZr2O7
    (Elsevier, 2011-08-01) Clements, R; Hester, JR; Kennedy, BJ; Ling, CD; Stampfl, APJ
    Twelve members of the Ho2-yNdyZr2O7 series, prepared using conventional solid state methods, have been characterised by neutron powder diffraction. Ho2Zr2O7 has a defect fluorite structure whereas Nd2Zr2O7 is found to adopt the ordered pyrochlore structure with the composition induced fluorite-pyrochlore transformation occurring near y=1. Rietveld analysis on the neutron data for all the compositions reveals an increase in lattice parameter as a function of y across the entire series, with a small discontinuity associated with the transformation. The neutron profile results suggest that domains of pyrochlore-type initially begin to form before crystallising into a separate phase, and therefore that anion and cation ordering processes are distinct. There is a strong correlation between the extent of disorder in the anion sublattice and the x-parameter of 48f oxygen. These results point the way to a better understanding of the stability observed in pyrochlore structures.(C) 2011 Elsevier Inc.
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    A neutron and synchrotron investigation of the electronic structure of lanthanide zirconates
    (Australian Institute of Physics, 2010-02-05) Clements, R; Kennedy, BJ; Ling, CD; Stampfl, APJ
    The lanthanide zirconates are of interest for use in inert matrix fuels and nuclear wasteforms. For use in these applications, the material's structure must be resistant to radiation damage and its thermal, thermodynamic and mechanical properties must be known. The structure's ability to incorporate an actinide host into the lattice vacancy must also be known. These properties may be better understood by investigating the f-electronic structure, which has historically proved difficult to model. We have undertaken a synthesis of the full range of lanthanide zirconate series using solid state techniques. We have performed neutron powder diffraction on a selection of the series in conjunction with the following measurements using synchrotron radiation: powder X-ray diffraction, VUV photoluminescence spectra, X-ray photoemission spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). These results will be presented, along with details of the analysis and synthetic techniques used.