Low temperature sol-gel preparation of β-Al₂TiO₅ thin films: spectroscopic analysis of the precursors

Two sol-gel syntheses allowed the preparation of β-Al₂TiO₅ thin films on silicon substrates at 700°C, reacting aluminum and titanium alkoxides with and without acetylacetone as a chelating agent. Nuclear magnetic resonance (NMR) and mass spectra of the sols allowed identification of the intermediate species formed and to show the formation of an Al-Ti containing polymer establishing that the synthesis without acetylacetone leads to the most extensive polymerization. The formation of β-Al₂TiO₅ at low temperatures is attributed to diffusion-limited crystallization process, which takes place in the conditions of high homogeneity at molecular level reached in the sol-gel synthesis. The crystallization of the films was studied as a function of the firing time and temperature and confirmed that β-Al₂TiO₅ with better thermal stability was obtained with the synthesis without chelating agent.