Thompson, Maria
(2010).
Synthesis and characterisation of d-Bi2O3 related materials stabilised by substitutions of Ca, Ga, Nb and Re.
University of Birmingham.
Ph.D.
Abstract
The work reported in this thesis is based around substitutions into bismuth oxide, which has proven to be highly adaptable chemically as it can accommodate a wide variety of substituents. The synthesis and characterisation of stabilised \(\delta\)-Bi\(_2\)O\(_3\) related materials containing small amounts of Ca, Ga, Nb and Re are described. A body of work is presented exploring the structural and physical properties of such materials, characterised by neutron powder diffraction, X-ray powder diffraction, electron diffraction, extended X-ray absorption of fine structure measurements, differential thermal analysis and impedance spectroscopy. The structure of two new fluorite-related materials, Bi\(_6\)Ca\(_3\)ReO\(_{15.5}\) and Bi\(_{10}\)Ca\(_5\)ReO\(_{23.5}\), were studied. Bi\(_6\)Ca\(_3\)ReO\(_{15.5}\) formed a face-centred cubic fluorite-related structure and Bi\(_{10}\)Ca\(_5\)ReO\(_{23.5}\) a body-centred cubic material that is a 4 x 4 x 4 superstructure of the Bi\(_6\)Ca\(_3\)ReO\(_{15.5}\) phase. The structure of novel isostructural materials Bi\(_{20}\)Ca\(_7\)NbO\(_{39.5}\) and Bi\(_{10.75}\)Ca\(_{4.375}\)GaO\(_{22}\) were also investigated. Both materials formed distorted \(\delta\)-Bi\(_2\)O\(_3\) related superstructures, derived as a monoclinic supercell based on a fluorite-related hexagonal subcell. Detailed structural analysis and local environments of cations in the ordered monoclinic fluorite-related superstructure of Bi\(_9\)ReO\(_{17}\) are also explored. All materials synthesised in this thesis have structures related to that of \(\delta\)-Bi\(_2\)O\(_3\), which is known to have high oxide ion conducting properties at elevated temperatures. Oxide ion conducting properties are therefore also described.
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