IMF2017

Recently, lead-free ferroelectric materials have attracted much attention from a view point of environmental protection. A BiFeO₃ (BFO) is one of the lead-free ferroelectrics, which shows an excellent ferroelectricity, and has been expected as a material for lead-free piezoelectric sensors, actuators, and vibration energy harvester. However, piezoelectric properties of BFO still remains unclear because growth of high-quality bulk ceramics is difficult. We have already demonstrated growth of single-crystal BFO thin films by sputtering. In this study, electric-field induced lattice distortion of BFO thin film was investigated by time-resolved X-ray diffraction under electric fields using a synchrotron radiation at BL13XU in SPring-8, Japan. The 1-μm-thick single-crystal BFO thin film was grown on SrRuO₃-buffered vicinal SrTiO₃ (STO) (001) substrate by rf sputtering. Pt top electrodes with a diameter of 200 μm were prepared by sputtering and lift-off process. The time–resolved X-ray diffraction measurement of the Pt/BFO/SRO/STO capacitor structure was performed under application of voltage pulses with an amplitude and width of 150 kV/cm and 300 ns, respectively. The synchrotron X-ray with an energy of 12.4 keV was focused within Pt top electrode in which electric field pulses are applied. Reciprocal space maps of BFO 003, 114, and 1-14 diffraction spots were observed by the time-resolved X-ray diffraction. Modulations of the BFO 003 and 114 diffraction spots were observed under the electric-field application. The lattice constants of the BFO with/without electric field indicates that the BFO lattice was expanded along vertical direction, and compressed along in-plane direction owing to the electric-field induced strain.