Low temperature sol-gel preparation of beta-Al2TiO5 thin films: Spectroscopic analysis of the precursors

Two sol-gel syntheses allowed the preparation of beta -Al2TiO5 thin films o n silicon substrates at 700 degreesC, reacting aluminum and titanium alkoxi des with and without acetylacetone as a chelating agent. Nuclear magnetic r esonance (NMR) and mass spectra of the sols allowed identification of the i ntermediate 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 beta -Al2TiO5 at low tempe ratures is attributed to diffusion-limited crystallization process, which t akes 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 beta -Al2T iO5 with better thermal stability was obtained with the synthesis without c helating agent.