Structure-Property Relationships in Oxide-Ion Conductors

Literature review: Details the structure-property relationships of a selection of oxide-ion conductors and their potential use as solid electrolytes. Experimental methods: Describes the synthesis methods and analytical techniques used during this project. Structural characterisation and properties of the Bi1–xNbxO1.5+x materials (x = 0.0625, 0.11, and 0.12): The characterisation of tetragonal Bi0.9375Nb0.0625O1.5625 is reported for the first time. Thermal annealing of Bi0.89Nb0.11O1.61 and Bi0.88Nb0.12O1.62 resulted in decreases in oxide-ion conductivity due to partial cubic-to-tetragonal phase transitions. The structure-property relationships of Bi(III)-containing apatite-type oxide-ion conductors: The first Bi(III)-containing triclinic apatite, Bi2La8[(GeO4)6]O3, was characterised, with annular bright-field scanning-transmission electron microscopy directly imaging small concentrations of interstitial oxygen. Bond valence energy landscape modelling probed the potential pathways for interstitial oxide-ion migration in apatites. Understanding variable Re coordination environments in Bi28Re2O49: Reverse Monte Carlo analyses of Bi28Re2O49 using neutron total-scattering data found the local-scale structure to contain 4-, 5-, and 6-coordinate ReOx polyhedra. At 700 °C, migration of oxygen atoms between the Bi-O and Re-O sublattices occurs. Structure-property relationships of bismuth molybdate compositions, Bi38–xMo7+xO78+3x/2 (x = 0, 0.5): The fluorite-related superstructure of orthorhombic Bi38Mo7O78 was characterised using synchrotron X-ray and neutron diffraction data, with distortion-mode analysis undertaken to attempt to characterise the room-temperature monoclinic phase. Floating-zone-furnace crystal growth of fluorite- and apatite-type oxide-ion conductors: Crystals for a range of materials were grown using a floating-zone furnace, upon which single-crystal Laue neutron diffraction data were subsequently collected. Using this data, the complex rhombohedral superstructure of Bi0.913V0.087O1.587 was characterised. Synthesis, characterisation, and properties of the LaxSr10–xGa6O19+x/2 family (x = 0, 0.2, and 0.4): A range of lanthanum strontium gallates were synthesised to investigate the effect of interstitial oxygen content on the oxide-ion conductivity of these materials. Conclusions and future work: A summary of the project, including suggestions for future work.