Ultrahigh energy storage and electrocaloric performance achieved in SrTiO3 amorphous thin films via polar cluster engineering

Lead-free film dielectric capacitors with fast charge/discharge capability are very attractive for advanced pulsed power capacitors, but lag behind in energy storage density. Here, we present an effective method to achieve high energy storage performance, which is embedding crystalline polar clusters in amorphous thin films. A large energy density of 65.3 J cm(-3), together with a high efficiency of 70.8% as well as excellent thermal stability, can be obtained in lead-free Sr-0.995(Na0.5Bi0.5)(0.005)(Ti0.99Mn0.01)O-3 amorphous thin films. It is revealed that anisotropic polar nanometer-scale regions caused by the crystalline polar clusters can be freely switched with the electric field and are not bound by the periodic structure of the crystals, thereby leading to large polarization in the amorphous thin films. Simultaneously, the amorphous thin films also possess good insulation, resulting in improved energy storage performance. Furthermore, a reversible negative electrocaloric effect (the adiabatic temperature change is about -10.6 K at 393 K and about -4.1 K at 300 K) is also obtained. This work provides a feasible and propagable method to develop multifunctional materials for applications in energy harvesting and modern solid state cooling.