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Browsing College of Arts and Science by Author "Aluri, Esther Rani"
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Item Assessing the oxidation states and structural stability of the Ce analogue of brannerite(Wiley, 2017) Aluri, Esther Rani; Bachiu, Lisa; Grosvenor, Andrew; Forbes, Scott; Greedan, JohnThe Ce‐containing analogue of brannerite (ie, UTi2O6) was previously considered to be stoichio- metric (ie, CeTi2O6); however, it has recently been determined that the material is O deficient. This oxygen‐deficient material has been suggested to be charged balanced by the presence of a minor concentration of Ce3+ or by the A‐site being cation deficient with the Ce oxidation state being 4+. A variety of Ti‐containing oxides (including brannerite) have been investigated as potential nuclear wasteforms, and it is necessary to understand the electronic structure of a proposed nuclear wasteform material as well as how the structure responds to radiation from incorporated waste elements. The radiation resistance of a material can be simulated by ion implantation. The objective of this study was to confirm the Ce oxidation state in the cation‐ and oxygen‐deficient material (ie, Ce0.94Ti2O6 − δ) and to determine how radiation damage affects this material. X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption near‐edge spectros- copy were used to study Ce0.94Ti2O6 − δ before and after being implanted with 2 MeV Au− ions. Analysis of the Ce 3d XPS spectra from the as‐synthesized samples by using a previously developed fitting method has unequivocally shown that Ce adopts both 4+ (major) and 3+ (minor) oxidation states, which was confirmed by examination of magnetic susceptibility data. Analysis of XPS and X‐ray absorption near‐edge spectroscopy spectra from ion‐implanted materials showed that both Ce and Ti were reduced because of radiation damage and that the local coordination environments of the cations are greatly affected by radiation damage.Item A study of the electronic structure and structural stability of Gd2Ti2O7 based glass-ceramic composites(the Royal Society of Chemistry, 2015) Aluri, Esther Rani; Grosvenor, AndrewGlass-ceramic composite materials have been investigated for nuclear waste sequestration applications due to their ability to incorporate large amounts of radioactive waste elements. Borosilicate- and Fe–Al–borosilicate glass-ceramic composites containing pyrochlore-type Gd2Ti2O7 crystallites were synthesized at different annealing temperatures and investigated by multiple techniques. Backscattered electron (BSE) images were collected to investigate the interaction of the pyrochlore crystallites with the glass matrix. Examination of the X-ray absorption near edge spectroscopy (XANES) spectra from the composite materials has shown how the glass composition, pyrochlore loading, and annealing temperature affects the chemical environment around the metal centers. These investigations have shown that the Gd2Ti2O7 crystallites can dissolve in the glass matrix depending on the glass composition and annealing temperature. The borosilicate glass composite materials were implanted with high-energy Au ions to mimic radiation induced structural damage. Surface sensitive glancing angle XANES spectra collected from the implanted composite materials have shown that structural damage of Gd2Ti2O7 occurs as a result of implantation, and that these materials show a similar response to ion implantation as Gd2Ti2O7 alone.