Preparation of LiNbO₃ thin films by Pechini method

Lithium niobate thin films have been deposited on Pt/Ti/SiO₂/Si (100) substrates by using Pechini method. The metal cations are chelated in an aqueous solution with citric acid as chelating agent. The chemistry of the metal-citric acid solutions has been characterized by carbon nuclear magnetic resonance spectroscopy (13C NMR), Raman spectroscopy and Fourier transform infrared (FTIR). A possible molecular structure of Nb-citric acid complex is proposed, i.e. citric acid coordinates to Nb⁵⁺ ion through one terminal carboxyl group, the hydroxyl group, and the central carboxyl group as a tridentate ligand. The thermal decomposition of Li-Nb precursors gels has been studied by TG/DTA and films annealed at different temperatures have been characterized by XRD and Roman spectroscopy. The results show that by heat-treatment at 600 °C for 2 h, polycrystalline LiNbO₃ thin films with smooth and crack-free surface could be achieved. The average grain size of the films is about 50 nm.