Transmission Electron Microscopic Studies of LiNb_0.5Ta_0.5O₃ Films Deposited on Sapphire Substrates by Thermal Plasma Spray CVD (Microstructure of LiNb_0.5Ta_0.5O₃ Films Deposited by Thermal Plasma Spray CVD)

Abstract

Cross sections and plan views of LiNb_0.5Ta_0.5O₃ films were investigated mainly by high-resolution transmission electron microscopy. These films were deposited on (0001) sapphire substrates by thermal plasma spray chemical vapor deposition method at various feeding rates of liquid raw materials. It was found that the crystallinity and the preferential orientation of the LNT films depend on the feeding rate. The LNT film formed at the feeding rate of 7 mL/min was epitaxially grown on the substrate, and the orientation relationship between the film and the substrate was (0001)_LNT⁄ ⁄(0001)_sapphire, [11\\bar20]_LNT⁄ ⁄[11\\bar20]_sapphire. The LNT films fabricated at the higher and the lower feeding rate were polycrystalline. These films included twin crystals and other phases such as Li(Nb, Ta)₃O₈. The calculations based on the coincidence of reciprocal lattice points revealed that the epitaxial orientation relationships observed by transmission electron microscopy satisfied the geometrically optimal coherency across the interface.