Synthesis, Structure and Properties of Mixed Metal Oxides: From Pyrochlores to Fluorites

Abstract

Introduction and Literature Review: Different families of oxide ion conductors and their applications are discussed. Experimental and Characterisation Methods: The synthetic methods and characterisation techniques used throughout this thesis are described. Synthesis, Structure and Transport Properties of Bi2Zr2-xTixO7 Phases: The characterisation of Bi2Zr2-xTixO7 compounds is reported for the first time. An increase in conductivity of 3 orders of magnitude is found for the Zr- rich end member. Bi2Ti2O7, which adopts centrosymmetric space group Fd-3m has been found to be SHG active. Structure Solution of beta-Bi2Sn2O7 and Properties of Bi2Sn2O7 Based Materials: Analysis of synchrotron powder X-ray and powder neutron diffraction data has shown for the first time that beta-Bi2Sn2O7 is not cubic and has a monoclinic structure, most likely in space group Pc. The effect of doping in both Bi2Sn2O7 and Bi2ScNbO7 on their respective conductivities has been explored. Synthesis and Characterisation of Nd2Zr2O7: A range of average and local structural techniques have been used to demonstrate that Nd2Zr2O7 prepared by wet-chemistry routes adopts the fluorite-type structure, as opposed to the pyrochlore structure adopted by samples synthesised by solid state methods. Synthesis, Characterisation, Simulations and Properties of Bi6WO12 and Related Oxide Ion Conductors: We report for the first time details of DFT molecular dynamics simulations to probe the oxide ion conduction pathways in the oxide ion conductor Bi6WO12. Appropriate doping has led to enhancements in oxide ion conductivity. Simulations, Characterisation and Properties of New Bismuth Vanadate Oxide Ion Conductors: DFT molecular dynamics simulations carried out on Bi19V2O33.5 have revealed the O2- migration pathways in this material with exceptional ionic conductivity. The synthesis and characterisation of new doped bismuth vanadates with formula Bi19-xMxV2O33.5-x/2 (M = Ca2+ or Sr2+), also excellent oxide ion conductors, is reported. Overall Conclusions and Suggestions for Future Work: This briefly reviews the conclusions and makes suggestions for further work