Control of Crystal Structure of BiFeO3 Epitaxial Thin Films by Adjusting Growth Conditions and Piezoelectric Properties

The effects of epitaxial strain on the crystal structure and piezoelectric properties of (100) BiFeO3 thin films were investigated. The epitaxial strain of BiFeO3 thin films grown by pulsed laser deposition was controlled by adjusting film thickness and growth temperature. From the results of X-ray diffraction reciprocal space mapping and in-plane piezoelectric force microscopy, it is found that the crystal structure of BiFeO3 thin films is a rhombohedral structure with tetragonal distortion, and that the extent of tetragonal distortion increases with decreasing film thickness and growth temperature. From the voltage-strain curves of the films, electric field strain is dominated by the piezoelectric effect in the low-voltage region, while the electrostrictive effect appears in the high-voltage region. It was found that piezoelectric strain increases with increasing extent of tetragonal distortion, which suggests that the piezoelectric properties of BiFeO3 thin films can be improved using a mixture of two types of structural distortion. (C) 2012 The Japan Society of Applied Physics