Ultrahigh energy storage performance via defect engineering in Sr_0.7Bi_0.2TiO₃ lead-free relaxor ferroelectrics

With the development of advanced electronic memory and the advocacy of environmental friendliness, lead-free relaxor ferroelectric capacitors with slim hysteresis loops have received great attention in high power energy storage applications. However, various emerging defects in Sr_0.7Bi_0.2TiO₃ based relaxor ferroelectric films can result in inferior energy storage performance. In this work, Mn doping is utilized to modify the defects caused by the excessive Bi compensation in the Sr_0.7Bi_0.2TiO₃ relaxor ferroelectric thin films. Those Mn doped Sr_0.7Bi_0.2TiO₃ thin films exhibits significantly improved recoverable energy storage density by more than one order of magnitude with an ultrahigh energy storage density (126 J/cm³). By analyzing the change of the chemical environment and using the scanning transmission electron microscopy, we reveal these improved energy storage performances arises from the formation of defect dipoles of Mn²⁺ at B site with oxygen vacancies, suppressing the volume of oxygen vacancies and titanium vacancies simultaneously, and the slush-like “single domain” structure with fluctuated B-site cation displacements stabilized and confined in a single nano-sized crystal grain. This chemical modification strategy in this work can serve as a regular approach to suppress the defects and improve the energy storage performance in ferroelectric thin films with volatile elements.