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8. An Improved Laboratory-Based XAFS and XES Spectrometer for Analytical Applications in Materials Chemistry Research

Author

Jahrman, Evan P., Holden, William M., Ditter, Alex S., Mortensen, Devon R., Seidler, Gerald T., Fister, Timothy T., Kozimor, Stosh A., Piper, Louis F. J., Rana, Jatinkumar, Hyatt, Neil C., and Stennett, Martin C.

Subjects
Condensed Matter - Materials Science
Abstract

X-ray absorption fine structure (XAFS) and x-ray emission spectroscopy (XES) are advanced x-ray spectroscopies that impact a wide range of disciplines. However, unlike the majority of other spectroscopic methods, XAFS and XES are accompanied by an unusual access model, wherein; the dominant use of the technique is for premier research studies at world-class facilities, i.e., synchrotron x-ray light sources. In this paper we report the design and performance of an improved spectrometer XAFS and XES based on the general conceptual design of Seidler, et al., Rev. Sci. Instrum. 2014. New developments include reduced mechanical degrees of freedom, much-increased flux, and a wider Bragg angle range to enable extended x-ray absorption fine structure (EXAFS) for the first time with this type of modern laboratory XAFS configuration. This instrument enables a new class of routine applications that are incompatible with the mission and access model of the synchrotron light sources. To illustrate this, we provide numerous examples of x-ray absorption near edge structure (XANES), EXAFS, and XES results for a variety of problems and energy ranges. Highlights include XAFS and XES measurements of battery electrode materials, EXAFS of Ni and V with full modeling of results to validate monochromator performance, valence-to-core XES for 3d transition metal compounds, and uranium XANES and XES for different oxidation states. Taken en masse, these results further support the growing perspective that modern laboratory-based XAFS and XES have the potential to develop a new branch of analytical chemistry.

Published
2018
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23. Analysis of the Structure of Heavy Ion Irradiated LaFeO3Using Grazing Angle X-ray Absorption Spectroscopy

Author

Townsend, Luke T., Corkhill, Claire L., Hewitt, David R., Gandy, Amy S., Hyatt, Neil C., and Stennett, Martin C.

Abstract

Crystalline ceramics are candidate materials for the immobilization of radionuclides, particularly transuranics (such as U, Pu, and Am), arising from the nuclear fuel cycle. Due to the α-decay of transuranics and the associated recoil of the parent nucleus, crystalline materials may eventually be rendered amorphous through changes to the crystal lattice caused by these recoil events. Previous work has shown irradiation of titanate-based ceramics to change the local cation environment significantly, particularly in the case of Ti which was shown to change from 6- to 5-fold coordination. Here, this work expands the Ti-based study to investigate the behavior in Fe-based materials, using LaFeO3as an example material. Irradiation was simulated by heavy ion implantation of the bulk LaFeO3ceramic, with the resulting amorphous layer characterized with grazing angle X-ray absorption spectroscopy (GA-XAS). Insights into the Fe speciation changes exhibited by the amorphized surface layer were provided through quantitative analysis, including pre-edge analysis, and modeling of the extended X-ray absorption fine structure (EXAFS), of the GA-XAS data.

Published
2024
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28. A multimodal X-ray spectroscopy investigation of uranium speciation in ThTi2O6 compounds with the brannerite structure.

Author

Dixon Wilkins, Malin C., Townsend, Luke T., Stennett, Martin C., Kvashnina, Kristina O., Corkhill, Claire L., and Hyatt, Neil C.

Subjects
CHEMICAL speciation, RAMAN spectroscopy, URANIUM, X-ray absorption, OXIDATION states, RADIOACTIVITY, X-ray spectroscopy
Abstract

ThTi2O6 derived compounds with the brannerite structure were designed, synthesised, and characterised with the aim of stabilising incorporation of U5+ or U6+, at dilute concentration. Appropriate charge compensation was targeted by co-substitution of Gd3+, Ca2+, Al3+, or Cr3+, on the Th or Ti site. U L3 edge X-ray Absorption Near Edge Spectroscopy (XANES) and High Energy Resolution Fluorescence Detected U M4 edge XANES evidenced U5+ as the major oxidation state in all compounds, with a minor fraction of U6+ (2–13%). The balance of X-ray and Raman spectroscopy data support uranate, rather than uranyl, as the dominant U6+ speciation in the reported brannerites. It is considered that the U6+ concentration was limited by unfavourable electrostatic repulsion arising from substitution in the octahedral Th or Ti sites, which share two or three edges, respectively, with neighbouring polyhedra in the brannerite structure. [ABSTRACT FROM AUTHOR]

Published
2023
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29. An Investigation of Iodovanadinite Wasteforms for the Immobilisation of Radio-Iodine and Technetium.

Author

Bailey, Daniel J., Johnstone, Erik V., Stennett, Martin C., Corkhill, Claire L., and Hyatt, Neil C.

Subjects
ISOSTATIC pressing, TECHNETIUM, HOT pressing, IODINE, FISSION products, SCANNING electron microscopy
Abstract

99Tc and 129I are two long-lived, highly soluble and mobile fission products that pose a long-term hazard. A proposed wasteform for the disposal of radio-iodine is iodovanadinite (Pb5(VO4)3I), an apatite-structured vanadate. In this investigation, a suite of potential iodovanadinite wasteforms designed for the co-disposal of Tc and I or the sole disposal of I were synthesised via hot isostatic pressing (with Mo as a surrogate for Tc). It was found that direct synthesis from oxide and iodide precursors was possible using hot isostatic pressing (HIPing). Increasing overpressure during HIPing was found to improve the density of the final product. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses indicated that the use of AgI as the source of iodine affected the formation of the target iodovanadinite phase and produced unfavourable phase assemblages. Here, we report the direct synthesis of Pb5(VO4)3I in a single step by hot isostatic pressing. [ABSTRACT FROM AUTHOR]

Published
2023
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33. Underpinning the use of indium as a neutron absorbing additive in zirconolite by X-ray absorption spectroscopy.

Author

Blackburn, Lewis R., Townsend, Luke T., Dixon Wilkins, Malin C., Ina, Toshiaki, Kuman, Merve, Sun, Shi-Kuan, Mason, Amber R., Gardner, Laura J., Stennett, Martin C., Corkhill, Claire L., and Hyatt, Neil C.

Subjects
X-ray spectroscopy, INDIUM, NEUTRONS, SOLID solutions, OXIDATION states, X-ray absorption
Abstract

Indium (In) is a neutron absorbing additive that could feasibly be used to mitigate criticality in ceramic wasteforms containing Pu in the immobilised form, for which zirconolite (nominally CaZrTi2O7) is a candidate host phase. Herein, the solid solutions Ca1-xZr1-xIn2xTi2O7 (0.10 ≤ x ≤ 1.00; air synthesis) and Ca1-xUxZrTi2-2xIn2xO7 (x = 0.05, 0.10; air and argon synthesis) were investigated by conventional solid state sintering at a temperature of 1350 °C maintained for 20 h, with a view to characterise In3+ substitution behaviour in the zirconolite phase across the Ca2+, Zr4+ and Ti4+ sites. When targeting Ca1-xZr1-xIn2xTi2O7, single phase zirconolite-2M was formed at In concentrations of 0.10 ≤ x ≤ 0.20; beyond x ≥ 0.20, a number of secondary In-containing phases were stabilised. Zirconolite-2M remained a constituent of the phase assemblage up to a concentration of x = 0.80, albeit at relatively low concentration beyond x ≥ 0.40. It was not possible to synthesise the In2Ti2O7 end member compound using a solid state route. Analysis of the In K-edge XANES spectra in the single phase zirconolite-2M compounds confirmed that the In inventory was speciated as trivalent In3+, consistent with targeted oxidation state. However, fitting of the EXAFS region using the zirconolite-2M structural model was consistent with In3+ cations accommodated within the Ti4+ site, contrary to the targeted substitution scheme. When deploying U as a surrogate for immobilised Pu in the Ca1-xUxZrTi2-2xIn2xO7 solid solution, it was demonstrated that, for both x = 0.05 and 0.10, In3+ was successfully able to stabilise zirconolite-2M when U was distributed predominantly as both U4+ and average U5+, when synthesised under argon and air, respectively, determined by U L3-edge XANES analysis. [ABSTRACT FROM AUTHOR]

Published
2023
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46. Cr2+ solid solution in UO2 evidenced by advanced spectroscopy.

Author

Smith, Hannah, Townsend, Luke T., Mohun, Ritesh, Cordara, Théo, Stennett, Martin C., Mosselmans, J. Frederick W., Kvashnina, Kristina, and Corkhill, Claire L.

Subjects
RADIOACTIVE waste management, SOLID solutions, URANIUM as fuel, RADIOACTIVE substances, NUCLEAR fuels, X-ray absorption near edge structure
Abstract

Advanced Cr-doped UO2 fuels are essential for driving safe and efficient generation of nuclear energy. Although widely deployed, little is known about their fundamental chemistry, which is a critical gap for development of new fuel materials and radioactive waste management strategies. Utilising an original approach, we directly evidence the chemistry of Cr(3+)2O3–doped U(4+)O2. Advanced high-flux, high-spectral purity X-ray absorption spectroscopy (XAS), corroborated by diffraction, Raman spectroscopy and high energy resolved fluorescence detection-XAS, is used to establish that Cr2+ directly substitutes for U4+, accompanied by U5+ and oxygen vacancy charge compensation. Extension of the analysis to heat-treated simulant nuclear fuel reveals a mixed Cr2+/3+ oxidation state, with Cr in more than one physical form, explaining the substantial discrepancies that exist in the literature. Successful demonstration of this analytical advance, and the scientific underpinning it provides, opens opportunities for an expansion in the range of dopants utilised in advanced UO2 fuels. Chromia is an important additive used in uranium dioxide fuel fabrication, but its incorporation mechanism is still not fully understood. Here, the authors use X-ray absorption spectroscopy, including both near edge and extended fine structure regions, to resolve the local structure and valence state of chromium, as divalent, in uranium dioxide. [ABSTRACT FROM AUTHOR]

Published
2022
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48. Defect Chemistry of Mn-Doped UO 2­

Author

Smith, Hannah, primary, Townsend, Luke T., additional, Mohun, Ritesh, additional, Radford, Joshua, additional, Stennett, Martin C., additional, Mosselmans, J. Frederick W., additional, Kvashnina, Kristina, additional, and Corkhill, C. L., additional

Published
2022
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