Perovskite Sr_1–<i>x</i>(Na_0.5Bi_0.5)_<i>x</i>Ti_0.99Mn_0.01O₃ 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 Sr_1-<i>x</i>(Na_0.5Bi_0.5)_<i>x</i>Ti_0.99Mn_0.01O₃ (<i>x</i> = 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 Na_Sr⁺ and Bi_Sr³⁺ 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 Sr_0.99(Na_0.5Bi_0.5)_0.01(Ti_0.99Mn_0.01)O₃ thin film with excellent energy-storage performance and the negative electrocaloric effect is a promising multifunctional material.