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

Abstract

TiO2 thin films prepared by metalorganic decomposition (MOD-TiO2) and sol-gel processes (SG-TiO2) were investigated in terms of the anatase-to-rutile phase transformation and microstructural evolution. It was found that the chemical reactivity of the ligand groups initially coordinated on the titanium precursor plays a decisive role in the structure development of as-deposited SG- and MOD-TiO2 films. MOD-TiO2 films consist of small aggregated particles and therefore, tend to coalesce together to form an inhomogeneous microstructure during the anatase-to-rutile phase transformation. On the other hand, SG-TiO2 films consist of uniform large particles that tend to grow homogeneously. MOD-TiO2 films showed a higher crystallization temperature than the SG-TiO2 films but the temperature of the anatase-to-rutile phase transformation is much lower in MOD- (approximately 775 °C) as compared to SG-TiO2 films (approximately 930 °C). The activation energy (Q) was estimated as 524 and 882 kJ/mol for the MOD- and SG-TiO2 films, respectively. The lower transformation temperature and activation energy in MOD-TiO2 films were due to smaller grain size and more potential nucleation sites existing in the un-transformed MOD-TiO2 film structure, which can accelerate the rate of anatase-to-rutile transformation.

Formation of nanoporous and nanocrystalline anatase films by pyrolysis of PEO–TiO2 hybrid films

“…The fraction values of anatase-to-rutile phase transformation were determined using following equation [11,16,17]:…”

“…Three different crystalline forms, brookite (orthorhombic, C21), anatase (tetragonal, C5), and rutile (tetragonal, C4), have been reported in TiO 2 , among which anatase shows the highest photocatalytic performances that is, high efficiency in photo-decomposition of harmful organic components. However, anatase in a powder form is not only apt to transform to rutile phase, but also easy to agglomerate at an elevated temperature [11][12][13][14][15][16][17]. Sintering of anatase powder into a bulk form can cause the significant deterioration in photocatalytic properties not only due to the phase transformation of anatase to rutile, but also due to the reduction in the surface to bulk ratio [18].…”

Hydrothermal growth of ferromagnetic Fe-doped TiO2 films

“…Normally, anatase films grown on fused silica substrates using metalorganic decomposition and sol-gel processes transform to the thermodynamically stable rutile phase at 760-850°C [16]. This indicates that epitaxy between the film and SrTiO 3 substrate stabilizes the metastable anatase phase even after annealing at 900°C for 10 h. The anatase phase is preferred to the rutile phase for epitaxy on the perovskite SrTiO 3 substrate as the lattice mismatch between the (001) oriented rutile structure and SrTiO 3 substrate is a much larger at 17.6%.…”

New TiO2 precursor for TiO2:poly(N-vinylcarbazole) (PVK) thin film: Synthesis and reactivity to hydrolysis of titanium tetrakis (9H-carbazole-9-yl-ethyl-oxy)

“…Ting and Chen [20] showed this influence in the structure development of as deposited sol-gel TiO 2 films. Bistan and Gomory [21] studied the reactions of hydrolysis of many titanium alkoxides and concluded that aryloxide titanium derivatives were less sensitive to hydrolysis than corresponding aliphatic alcohols.…”