Hydrothermal synthesis of (00l) epitaxial BiFeO3 films on SrTiO3 substrate

Epitaxial thin films of multiferroic BiFeO3 (BFO) are successfully grown on (100) SrTiO3 substrates using a hydrothermal synthesis method at 120–200 °C in a relatively short time of 2–8 h. It is found that the morphology evolution of the (001)PC-oriented BFO films over time and temperature involve unique dissolution–reprecipitation reactions, whereby initial large sparse islands dissolve, and re-precipitate into dense mosaic-like structures that further grow vertically, resembling those of terrace-like structures. High-resolution transmission electron microscopy (HRTEM) and ψ-ω-2θ high resolution thin film X-ray diffraction scans suggest that the BFO films have relaxed to a monoclinic structure—different from the rhombohedral bulk BFO powders. Peak fittings of the powders and films reveal that the lattice parameters contract when either reaction time or temperature is increased. Similar lattice contraction is also observed when the films/powder are annealed at 550 °C in N2 atmosphere for 10 min. Dielectric constant and loss, leakage current and ferroelectric properties of the BFO film improve with annealing, attributed to a reduced amount of defects.