Doctoral Dissertations

Date of Award

12-2023

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Nuclear Engineering

Major Professor

Maik Lang

Committee Members

Gianguido Baldinozzi, Kurt Sickafus, Steven Zinkle, Christina Trautmann, Matthew Tucker

Abstract

Weberite-type A3BO7 oxides, where A is a trivalent rare earth and B is a pentavalent element like Ta, have been a focus of research due to the discovery of the weberite-type local atomic arrangement in ceramics with a defect-fluorite structure. Earlier studies primarily examined their long-range structures, leaving gaps in understanding their short-range atomic behavior. This thesis investigates various weberite-type tantalates across all structural scales. There has been debate over the long-range structure of Y3TaO7, a medium-sized rare earth tantalate oxide, particularly regarding its spacegroup symmetry. This work identifies Y3TaO7 as an outlier, with neutron total scattering and DFT calculations indicating the C2221 spacegroup as the most fitting for its structure at both local and long-range levels.

The thesis extends this structural analysis to a series of Ln3TaO7 weberite-type oxides. Neutron- and X-ray total scattering experiments reveal these materials' complexity and establish a link between short- and long-range order. It is found that local distortions and the averaging of local atomic domains lead to distinct structural families in weberite-type oxides. A new experimental framework is developed to systematically explore local symmetries and derive accurate local atomic models, using a novel correlated differences approach.

Additionally, the thesis explores the behavior of weberite-type oxides under swift heavy ion radiation, a previously unexamined area. It shows that while the long-range structures of weberite-type and pyrochlore oxides respond similarly to radiation, their short-range local atomic configurations differ post-irradiation, with weberite-type oxides maintaining configurations similar to their non-irradiated state.

In summary, this comprehensive study of weberite-type oxides' structures and radiation resistance emphasizes the importance of local atomic arrangements in understanding complex oxides. It demonstrates that these arrangements significantly affect amorphization resistance. The methodologies and insights gained are applicable to other materials, opening avenues for further research.

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