Defect and texture engineering of relaxor thin films for High-Power energy storage applications

Relaxors are a family of polar-oxides with a high degree of chemical disorder and nanosized domains. A characteristic feature of relaxors is their slim polarization–electric field hysteresis loop, which makes them effective in high-power energy storage applications requiring fast (dis)charging, such as electric vehicles, smart grids, RFID technologies, and pulsed-power devices. Interest in relaxor thin films is also driven by a push to reduce overall device size and enhance energy efficiency. Improved long-term reliability is essential for using oxide thin films in devices. However, ionic vacancies and defect complexes formed during fabrication invariably affect oxide thin-film electrical properties. Such defects affect the long-term polarization properties of ferroelectric-oxides with micron-sized domains via mechanisms such as domain-wall pinning. However, the relaxor's nanoscale domains are highly dynamic, making domain-boundaries pinning negligible. Although it is generally accepted that defects significantly affect relaxor thin-film properties, the specific roles of defects in relaxor thin films are still obscure. This review deliberates the fundamentals and recent advances in engineering relaxor thin-film defects to improve their electrostatic energy storage properties (ESP) over broad operating conditions. In addition, we explore the possibility of tuning other degrees of freedom, such as the preferred crystallographic orientation of grains that may augment the ESP of relaxor thin films. The study concludes with a perspective on how the issues facing the adoption of relaxor thin films in energy storage devices can be overcome by a better understanding of their microscopic charge compensation mechanisms and intelligent exploitation of their anisotropic dielectric properties.