Microstructure development of BiFeO3-PbTiO3 films deposited by pulsed laser deposition on platinum substrates

摘要

BiFeO3-PbTiO3 films around the morphotropic phase boundary were deposited by pulsed laser deposition on polycrystalline Pt/TiOx/SiO2/Si substrates. X-ray analysis confirms that 0.6BiFeO3-0.4PbTiO3 films are (0 0 1) tetragonal preferentially orientated due to lattice matching with the underlying substrate. The misfit strain at the substrate-film interface is relieved by a ∼19% orientation transformation from (0 0 1) to (1 0 0) due to the lattice mismatch at the substrate-film interface and the difference in thermal expansion coefficients of the substrate and deposited film. 0.7BiFeO3-0. 3PbTiO3 films are mixed-phase rhombohedral-tetragonal with (0 0 1)/(1 1 1) preferential orientation due to the lattice match to the (1 1 1) and (1 0 0) of the underlying platinum as well as to being close to the morphotropic phase boundary. Inconsistent structural and electrical properties in reported BiFeO3-PbTiO3 films are explained in terms of film morphology and diffusion of bismuth into platinum. Films below ∼220 nm thickness produce short circuits due to a Volmer-Weber growth mechanism which results in physical defects within the films. Films above this critical thickness also produce variable electrical properties due to diffusion of bismuth into the underlying platinum electrode which has been confirmed by energy dispersive X-ray spectroscopy.