Structural and electronic investigation of Li2O-TiO2 system
Yıldızhan, Melike Mercan (2016) Structural and electronic investigation of Li2O-TiO2 system. [Thesis]
TiO2-anatase is a material of importance for energy applications, such as DSSC. It was observed that the efficiency of DSSC increases with Li-doping. However, incorporation mechanism of Li into/onto TiO2 and the extent of Li-uptake still remain unclear, mostly due to the difficulty of detecting Li. Previous studies utilized techniques, which do not allow analysis on individual particles. The scope of this study is to elucidate the interaction of TiO2 crystal structure with Li by investigating the Li2O-TiO2 system. Doping experiments were performed to find the solubility limit of Li in anatase by solid-state and sol-gel techniques. TiO2 was also doped with two different model cations, K and Nb to see the effect of size and charge of dopant, respectively. A successive-surface-etching technique was coupled to ICP-OES to determine the solubility limits of Li and K or EDX for that of Nb in TiO2. The effects of dopants on the crystal-structure and crystal-symmetry were followed by XRD and Raman Spectroscopy, respectively. Electronic structure modifications upon doping were followed by UV-Visible spectroscopy and EELS. The low solubility of Li compelled to use the compounds in the phase diagram as signature signals for EELS investigations. Li-K, Ti-L2,3 and O-K edges of compounds with different Li:Ti ratios/crystal structures were determined as fingerprints. It was observed that O-K edge is the most sensitive to the alterations in the crystal/electronic structure. Our experimental results showed that Li is mostly accommodated at the surfaces of nanoparticles. The Li-uptake of crystal structure is limited to 0.7cation%.
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