Titanium Oxide Nanoparticles Precipitated from Low‐Temperature Aqueous Solutions: III. Thin Film Properties

Abstract

In our previous reports (Part I and II), we have identified precursor “supersaturation” as a key parameter to control the precipitation behavior of titania nanoparticles in a temperature‐driven hydrolysis process from the chemical bath of soluble titanium salt. Through this protocol, a methodology was developed to grow titania films with controlled microstructures and phases. In this study, we deposited titania films containing anatase or rutile as a dominant phase along with microstructures of various film densities, which were characterized for their dielectric, optical, photoelectrochemical, and mechanical properties. Specific microstructures and the constituting phases were responsible for a wide variation of such properties of titania thin films. This study aims to provide the systematic explanation for evolution of the phases as a function of the degree of supersaturation, along with the discussion of their effects on the aforementioned engineering properties.

Precipitation Mechanisms of Mesoporous Nanoparticle Aggregates: Off-Lattice, Coarse-Grained, Kinetic Simulations

“…3 Being able to tailor this mesostructure would help improving the strength, functionality, and durability of important engineering materials, such as mesoporous metal oxides, zeolites, and cement paste. 4,5 The current approaches to mesostructural optimization are mostly empirical [6][7][8] . What is missing is a theoretical understanding of the relationship between mechanisms of nanoparticle precipitation/aggregation and experimental synthesis variables, such as solution chemistry and temperature.…”

Grain size reduction on nanostructured TiO2 thin films due to annealing

“…In other words, chemical potential, and the number of moles, or equivalently the chemical activities of the reactants, and products can play a signicant role in the phase, and shape of the deposited TiO 2 lms. Roy et al 25 have studied not only the deposition conditions but also the properties of TiO 2 thin lms produced by solution bath deposition method. This can be translated as another term in eqn (1).…”

Hierarchical Organization of TiO2 Nanostructures in Low‐Temperature Solution Processes

“…After hydrolysis reaction of TiCl 4 in aqueous solution, Ti ion can exist in a basic monomeric [Ti(O)(H 2 O) 5 ] 2+ form and this sixfold coordinated structure becomes octahedrons after the condensation reactions. The formation of crystalline phase would then be governed by pH . At lower supersaturation (i.e., lower pH) during the solution process, the condensation reaction would be hindered by a repulsion force from the adsorbed H + ions so the precipitation should occur slowly and the rutile structure can be attained.…”

“…There are three common types of crystalline phases (rutile, anatase, and brookite), each of which shows unique properties. Especially rutile is thermodynamically the most stable phase compared to the other two polymorphs, often being considered for electrical and optical ceramic materials . On the other hand, the anatase phase is thermodynamically metastable at ambient conditions and has been reported that it exerts higher performance as a photocatalytic material and gets even better when mixed with a rutile structure .…”

“…Specific phases (rutile, anatase, and amorphous) and nanostructures (tree, leaf, and particle shape) of TiO 2 thin films were derived by adjusting the degrees of supersaturation of precursor solutions from 70 to 200 . Those nanostructured TiO 2 thin films showed promising performance suitable for high‐k dielectric and photovoltaic applications . In this work, we have employed the CBD and the hydrothermal process to generate even lower degrees of supersaturation ( s ≤ 70) to trigger the anisotropic growth of nanostructures.…”