Influence of ligand groups in Ti precursors on phase transformation and microstructural evolution of TiO2 thin films prepared by the wet chemical process

TiO2 thin films prepared by metalorganic decomposition (MOD-TIO,) and sol-g el processes (SG-TiO2) were investigated in terms of the anatase-to-rutile phase transformation and microstructural evolution. It was found that the c hemical reactivity of the ligand groups initially coordinated on the titani um precursor plays a decisive role in the structure development of as-depos ited SG- and MOD-TiO2 films. MOD-TiO2 films consist of small aggregated par ticles and therefore, tend to coalesce together to form an inhomogeneous mi crostructure during the anatase-to-rutile phase transformation. On the othe r hand, SG-TiO2 films consist of uniform large particles that tend to grow homogeneously. MOD-TiO2 films showed a higher crystallization temperature t han the SG-TiO2 films but the temperature of the anatase-to-rutile phase tr ansformation is much lower in MOD- (approximately 775 degreesC) as compared to SG-TIO, films (approximately 930 degreesC). The activation energy (Q) w as estimated as 524 and 882 kJ/mol for the MOD- and SG-TIO, films, respecti vely, The lower transformation temperature and activation energy in MOD-TiO 2 films were due to smaller grain size and more potential nucleation sites existing in the un-transformed MOD-TiO2 film structure, which can accelerat e the rate of anatase-to-rutile transformation.