High energy storage density and a reversible electrocaloric effect are simultaneously achieved in Sr0.995(Na0.5Bi0.5)0.005(Ti0.99Mn0.01)O3 amorphous thin films via polar cluster engineering.

Srx(Na0.5Bi0.5)1−xTi0.99Mn0.01O3 (x = 0.2, 0.4, 0.6, and 0.8) relaxor ferroelectric thin films were grown on Pt/Ti/SiO2/Si substrates by the Sol-Gel method. The influence of the Sr content on the microstructures, ferroelectric properties, and energy-storage performances of the thin films were investigated in detail. The Sr0.6(Na0.5Bi0.5)0.4Ti0.99Mn0.01O3 thin film exhibits very slim hysteresis loops with the highest electric breakdown field strength due to reduced oxygen vacancies. Owing to the high breakdown field strength of 3134.3 kV/cm, the Sr0.6(Na0.5Bi0.5)0.4Ti0.99Mn0.01O3 thin film shows a giant recoverable energy-storage density of 33.58 J/cm3. These results indicate that the Sr0.6(Na0.5Bi0.5)0.4Ti0.99Mn0.01O3 thin film is promising for applications of advanced capacitors with high energy-storage density.

Dielectric capacitors have received more and more attention because of fast charge/discharge capability. However, the energy-storage performance still cannot meet the demand. In this work, lead-free perovskite Sr1–x (Na0.5Bi0.5) x Ti0.99Mn0.01O3 (x = 0, 0.005, 0.01, and 0.02) thin films prepared by the sol–gel method were carefully studied. Defect dipoles and local lattice distortion were created by doping Mn at the B-site, enabling ferroelectric polarization behavior. To further enhance polarization, co-substitution at the A-site was adopted. Na+ and Bi3+ can make up Na+–Bi3+ ion pairs. Meanwhile, off-center NaSr + and BiSr 3+ ions with a small radius can lead to the distortion of the octahedral [TiO6] in the lattice to induce local polarization regions. Under the combined action of A-site and B-site doping, polarization and breakdown strength were greatly improved. Finally, a high energy density (53 J cm–3) and good thermal stability were achieved. Furthermore, the negative electrocaloric effect was also achieved. The adiabatic temperature change is about −8.5 at 300 K. This work demonstrates that the Sr0.99(Na0.5Bi0.5)0.01(Ti0.99Mn0.01)­O3 thin film with excellent energy-storage performance and the negative electrocaloric effect is a promising multifunctional material.

No abstract