A Sol-Gel Technology for Creating Thin-Film Oxide Materials for a Variety of Uses: A Brief Review

The sol-gel process for making thin-film oxide materials is a low-cost and versatile way of creating nanostructures. This method provides a uniform distribution of elements of multicomponent systems over the surface of various solids. The thickness and morphology of the surface of oxide films are largely determined by the composition, structure, and processes occurring in the sols from which the films are obtained. The selection of precursors is essential in this method to acquire the desired composite oxide materials. In this paper, we present an overview of the results of studies on the sol-gel production of thin-film oxide materials based on SiO2–ExOy (E = a rare earth element (REE), Sn, Mn, Co, Ni, Ca, P), TiO2–ExOy (E = Si, Sn, Co, Ni), SnO2–ExOy (E = In, Sb, Ce), and ZrO2. In the main part of the work, we consider sol-gel processes (hydrolysis, polycondensation, complex formation) involving tetraethoxysilane, tetrabutoxytitanium, antimony(III), and tin(II, IV) acetylacetonate complexes, as well as polynuclear zirconium(IV) clusters. We explore the processes of obtaining a sol, leading to its film-forming ability, the composition of micelles, the size of colloidal particles, and the change in the composition of micelles when an additive is introduced to the tetraethoxysilane-based sol. We discuss the effect of adding salts of various natures, organic ligands, and solvents on the time stability of sols. We then consider the effect of the hydrolyzing ability of doubly charged nickel, manganese, and cobalt cations on the rate of hydrolysis and polycondensation of tetraethoxysilane. Based on the studies mentioned above, we propose a general technological approach for creating sols that are resistant to film formation, using the example of tetraethoxysilane and tetrabutoxytitanium sols. We consider the relationship between the network structure of a tetraethoxysilane sol and the network structure of oxide films by the example of SiO2–CeO2, SiO2–NiO, SiO2–Mn2O3, and SiO2–Co3O4. The effect of the rate of thermal treatment of gels on the morphology of oxide films is also studied.