Flexoelectricity-driven giant polarization in (Bi, Na)TiO3-based ferroelectric thin films

This study demonstrates the use of oxygen vacancy-induced planar defects to significantly enhance electrical polarization through a local flexoelectric effect. By introducing an appropriate level of aliovalent dopants, numerous local planar defects are induced in (Bi _0.5 , Na _0.5 )TiO ₃ -based thin films. These defects, identified as oxygen-deficient structures through direct visualization of oxygen atoms and oxygen vacancies using integrated differential phase-contrast (iDPC) microscopy, result in the formation of head-to-head (H-H) domain structures. Geometric phase analysis (GPA) confirms that these structures exhibit a substantial local strain gradient of up to 10 ⁹ m ^− 1 , contributing significantly to the flexoelectric polarization. Consequently, a giant maximum polarization ( P _m ) of 161 µC cm ^− 2 under 750 kV cm ^− 1 and a remanent polarization P _r =115 µC cm ⁻² along with a coercive field of 250 kV cm ⁻¹ are achieved, allowing these BNT-based thin films to be used in low-power electronic applications. Crucially, the P _m and P _r of the thin films can be sustained at 133 and 98 µC cm ⁻² , respectively, at 230°C. Additionally, they exhibit exceptional high-temperature fatigue endurance, with P _m and P _r demonstrating a negligible reduction of less than 9% after 10 ⁷ cycles under 750 kV cm ⁻¹ at 230°C. To the best of our knowledge, these values establish a new record for oxide perovskite thin films at elevated temperatures, demonstrating potential applications of our thin films in high-temperature environments. Our findings offer promising avenues for advancing the application fields of ferroelectric thin films.