Perovskite Sr1-x(Na0.5Bi0.5)xTi0.99Mn0.01O3 Thin Films with Defect Dipoles for High Energy-Storage and Electrocaloric Performance.

Abstract

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)xTi0.99Mn0.01O3 (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 BiSr3+ 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.