Structure-property relationships of uranium and technetium-containing oxides.

Abstract

Metal oxides, such as perovskites, are flexible materials in which a large range of properties can be accessed and tuned. This flexibility results in ideal materials for the study of structure and properties. Understanding structure-property relationships underpins the understanding of functional materials - and provides the fundamental motivation for this work. The work described in the first part of this thesis focuses solely on the evaluation of the ambient structures of some uranium double perovskites, and their behaviour at elevated temperatures. The results nicely complement, as well as contribute to, the current literature. The bulk of this work, however, involves the study of Tc-containing oxides. Due to the challenges associated with the synthesis and characterisation of active materials, the perovskite systems described, although simple, have never before been studied. Therefore, this thesis describes the first known work on the tertiary systems Ba(x)Sr(1-x)TcO3 and SrTc(x)Ru(1-x)O3. Both systems exhibit an intimate relationship between the structure and magnetism. Finally, the unusual transition in a Ru-containing hexagonal perovskite Ba3BiRu2O9 is studied. Total scattering neutron data is analysed using the reverse Monte Carlo (RMC) modelling technique, providing information on the local structure otherwise inaccessible using traditional diffraction analysis.