Browsing by Author "Oldfield, DT"
Now showing 1 - 3 of 3
Results Per Page
- ItemInsight Into disorder, stress and strain of radiation damaged pyrochlores: a possible mechanism for the appearance of defect fluorite(Frontiers Media S.A., 2021-11-08) Finkeldei, SC; Chang, S; Ionescu, M; Oldfield, DT; Davis, J; Lumpkin, GR; Simeone, D; Avdeev, M; Brandt, F; Bosbach, D; Klinkenberg, M; Thorogood, GJWe have examined the irradiation response of a titanate and zirconate pyrochlore—both of which are well studied in the literature individually—in an attempt to define the appearance of defect fluorite in zirconate pyrochlores. To our knowledge this study is unique in that it attempts to discover the mechanism of formation by a comparison of the different systems exposed to the same conditions and then examined via a range of techniques that cover a wide length scale. The conditions of approximately 1 displacement per atom via He2+ ions were used to simulate long term waste storage conditions as outlined by previous results from Ewing in a large enough sample volume to allow for neutron diffraction, as not attempted previously. The titanate sample, used as a baseline comparison since it readily becomes amorphous under these conditions behaved as expected. In contrast, the zirconate sample accumulates tensile stress in the absence of detectable strain. We propose this is analogous to the lanthanide zirconate pyrochlores examined by Simeone et al. where they reported the appearance of defect fluorite diffraction patterns due to a reduction in grain size. Radiation damage and stress results in the grains breaking into even smaller crystallites, thus creating even smaller coherent diffraction domains. An (ErNd)2(ZrTi)2O7 pyrochlore was synthesized to examine which mechanism might dominate, amorphization or stress/strain build up. Although strain was detected in the pristine sample via Synchrotron X-ray diffraction it was not of sufficient quality to perform a full analysis on. Copyright © 2021 Finkeldei, Chang, Ionescu, Oldfield, Davis, Lumpkin, Simeone, Avdeev, Brandt, Bosbach, Klinkenberg and Thorogood.
- ItemNanoporous zirconium phosphonate materials with enhanced chemical and thermal stability for sorbent applications(American Chemical Society, 2020-04-01) Veliscek-Carolan, J; Rawal, A; Oldfield, DT; Thorogood, GJ; Bedford, NMNanoporous zirconium phosphonate (ZrP) materials are considered to be promising candidates for practical applications such as catalysis and separation, in particular because of their excellent stability, resulting from the strength of the P–O–Zr bond. However, the functionality of ZrP materials is dependent on the availability of free phosphonate groups uncoordinated by zirconium, the presence of which can decrease the stability. The mechanisms by which nanoporous ZrP materials degrade and lose functionality during thermal and chemical treatment are not well understood. Herein, we address this knowledge gap using nanoporous zirconium aminotris(methylenephosphonic acid) (Zr-ATMP) sorbent materials. Thermal treatment up to 150 °C caused collapse of the nanoporous structure of some Zr-ATMP materials without a significant effect on the chemical structure. On the other hand, contact with 5 M nitric acid changed the chemical structure of the Zr-ATMP materials by catalyzing the formation of P–O–Zr bonds and elemental leaching. Enhancement of the thermal and chemical stability of the Zr-ATMP materials was achieved by decreasing the pH of the synthesis and, interestingly, changing the counterion of the hydroxide used to control the pH also impacted the structure and stability of the resulting materials. The most stable Zr-ATMP material was produced at pH 3 using LiOH, but this material demonstrated lower selectivity than other Zr-ATMP materials, which decreases its practicality for separation applications. The Zr-ATMP material synthesized at pH 3 with NaOH showed an optimal balance between the stability and sorption performance. The enhanced chemical and thermal stability of this material drastically improves its applicability for use in harsh environments, such as in the treatment of radioactive wastes. © 2020 American Chemical Society
- ItemTotal scattering measurements at the Australian Synchrotron Powder Diffraction beamline: capabilities and limitations(International Union of Crystallography, 2023-03-01) D'Angelo, AM; Brand, HEA; Mitchell, VD; Hamilton, JL; Oldfield, DT; Liu, ACY; Gu, QFThis study describes the capabilities and limitations of carrying out total scattering experiments on the Powder Diffraction (PD) beamline at the Australian Synchrotron, ANSTO. A maximum instrument momentum transfer of 19 Å−1 can be achieved if the data are collected at 21 keV. The results detail how the pair distribution function (PDF) is affected by Qmax, absorption and counting time duration at the PD beamline, and refined structural parameters exemplify how the PDF is affected by these parameters. There are considerations when performing total scattering experiments at the PD beamline, including (1) samples need to be stable during data collection, (2) highly absorbing samples with a μR > 1 always require dilution and (3) only correlation length differences >0.35 Å may be resolved. A case study comparing the PDF atom–atom correlation lengths with EXAFS-derived radial distances of Ni and Pt nanocrystals is also presented, which shows good agreement between the two techniques. The results here can be used as a guide for researchers considering total scattering experiments at the PD beamline or similarly setup beamlines. © 2023 The Authors - Open Access CC-BY Licence 4.0