Synthesis and characterisation of niobium doped TiO2 semiconducting materials
This thesis focuses on synthesis and characterisation of niobium doped TiO2 materials as thin films, nanorods and nanopowders and their applications as windows coatings, transparent conducting oxide (TCO) materials and anodes for lithium ion batteries. The first chapter gives an introduction to the TCO materials, TiO2 characterisation, application and doping methods. It also contains a brief description of the synthesis and analysis methods, used in the thesis. The second chapter describes the niobium doped anatase form of TiO2 thin films deposited via aerosol assisted chemical vapour deposition (AACVD) on silica coated glass. The as deposited films were blue, largely transparent in the visible region, reflective in the IR region and electrically conductive. The doping progress and phase segregation propagation were analysed using high resolution transmission electron spectroscopy (HR TEM) and X ray absorption spectroscopy (XAS) In the third chapter, AACVD deposition of TiO2 and niobium doped TiO2 over a fluorine doped tin oxide (FTO) substrate in order to achieve the rutile form of TiO2 by templating the lattice structure is described. Depending on the synthesis precursors and temperatures used, the obtained films consisted of one to four different parts, varying from a metallic continuous tin film, mixture of rutile TiO2, FTO and metallic tin to layered FTO anatase TiO2 thin films. In order to increase the photocatalytic properties of the anatase thin films described in the second chapter a silver layer was sputtered prior to the AACVD deposition of both pristine and niobium doped TiO2 thin films. While the Ag:TiO2 thin films remained electrically insulating, the Ag:NbTiO2 thin film displayed electrical conductivity. For both films the rate of photo degradation of Resazurin dye was lower than that of a Pilkington Activ(tm) standard. The fifth chapter describes the hydrothermal synthesis method of both rutile and anatase TiO2 powders, by changing the pH of the process. The successful substitutional doping of niobium into the TiO2 lattice was obtained at temperatures as low as 180 degC. The differences in phase segregation in rutile and anatase are described. Chapter six describes the hydrothermal synthesis of the Nb:TiO2 rutile free standing film, 10 um thick, with rutile rods creating a stable and merged structure, that maintains flexibility and can be shaped within a two minute exposure window to the air.