Amorphous/Crystalline Engineering of BaTiO3-Based Thin Films for Energy-Storage Capacitors

The trade-off relationship of the polarization and the breakdown strength severely limits the enhancement of energy-storage properties of dielectric materials. In this work, Pb-free 0.92BaTiO3–0.08Bi(Mg1/2Zr1/2)O3 (0.92BT-0.08BMZ) thin films are synthesized via a sol–gel method, in which the coexisting state of an amorphous phase and a crystalline phase is achieved and regulated through changing the annealing temperature. First, Pt/Ti/SiO2/Si is selected as a substrate due to the favorable phase composition and the optimized energy-storage properties, compared to LaNiO3-buffered Si and Nb:SrTiO3 substrates. Second, the evolution from the single amorphous phase to the amorphous/crystalline coexisting phase driven by increasing the annealing temperature is proved by grazing incident X-ray diffraction (GIXRD), high-resolution TEM (HRTEM), and an enhanced dielectric constant for 0.92BT-0.08BMZ thin films. Additionally, the local electric field and the polarization with 0.92BT-0.08BMZ thin films at different annealing temperatures are analyzed based on finite element simulation, revealing that the regulation of the ratio of the nanocrystal phase in the amorphous phase matrix would be effective in enhancing the energy-storage density. Finally, the optimized energy-storage performance is achieved in 0.92BT-0.08BMZ thin films annealed at 600 °C, with a large energy density of 55.2 J/cm3 and a high energy efficiency of 83.6%, demonstrating the great application potential of 0.92BT-0.08BMZ thin films for portable pulse capacitors.