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Title: Structural and compositional studies of novel ribbon structures
Author: Bennett, J. E.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2002
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This thesis documents the results of a structural and compositional study of selected mixed metal oxides possessing novel structures based upon 'ribbons' of corner sharing metal-oxygen octahedra. The techniques employed to characterise the specimens of interest have included Powder X-ray Diffraction (PXRD). High Resolution Transmission Electron Microscopy (HRTEM) and Energy Dispersive X-ray Spectroscopy (EDS). Compositional analysis of specimens containing strontium, lanthanum and titanium has been achieved to a high degree of accuracy using EDS analysis in the electron microscope. A mathematical technique based upon the intensity ratios of the X-ray emission lines has been developed to overcome the problem of overlapping lanthanum L and titanium K peaks in the X-ray emission specimen. The viability of the new technique has been proven using well characterised test specimens containing all three elements. An in-depth study of two compounds in the SrO-La2O3-TiO2 system, Sr3La2Ti2O10 and Sr8La4Ti5O24 has been performed. Evidence from high resolution imaging and electron diffraction has confirmed that threes phases possess composite layer structures based upon corner sharing ribbons of TiO6 octahedra. Their status as the n=4 and n=5 members of a homologous series Sr2n-2La4TinO4n+4, where the parameter n represents the number of TiO6 octahedra in the ribbons, has also been established using EDS. However, results also suggest that these compounds may be metastable. The effect of niobium substitution on the structure of the n=1 Aurivillius phase, Bi2WO6, has also been investigated. Results from HRTEM have shown up to 25% of the tungsten can be substituted by niobium without any observable effect on the Aurivillius structure. Upon 50% niobium substitution, it appears that a structural modification takes place, as high resolution imaging and electron diffraction reveal a superstructure on the (012) or (013) planes of a Bi2WO6 sub-cell, which can be attributed to the presence of steps in the Aurivillius matrix at regular intervals.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available