Synergically improved energy storage performance and stability in sol–gel processed BaTiO <sub>3</sub>/(Pb,La,Ca)TiO <sub>3</sub>/BaTiO <sub>3</sub> tri-layer films with a crystalline engineered sandwich structure
Jinpeng Liu, Ying Wang, Hanfei Zhu, Hong Luo, Xiao Zhai, Yu Huan, Jing Yan, Kun Wang, C. H. Liu, Hongbo Cheng, Jun Ouyang
Abstract
Achieving an excellent energy storage performance, together with a high cycling reliability, is desirable for expanding the technological applications of ferroelectric dielectrics. However, in a well-crystallized ferroelectric material, the concomitant high polarizability and low polarization-saturation field have led to a square-shaped polarization-electric field loop, fatally impairing both recoverable energy density (<em>W</em><sub>rec</sub>) and efficiency (<em>η</em>). Nanocrystalline ferroelectric films with a macroscopically amorphous structure have shown an improved <em>W</em><sub>rec</sub> and <em>η</em>, but their much-lower polarizability demands an extremely high electric field to achieve such performances, which is undesirable from economical viewpoints. Here, we propose a strategy to boost the energy storage performances and stabilities of ferroelectric capacitors simultaneously by constructing a tri-layer film in which a well-crystallized ferroelectric layer was sandwiched by two pseudo-linear dielectric layers with a dominant amorphous structure. In sol-gel-derived BaTiO<sub>3</sub>/(Pb,La,Ca)TiO<sub>3</sub>/BaTiO<sub>3</sub> (BTO/PLCT/BTO) tri-layer films, we show that the above design is realized via a rapid thermal annealing which fully crystallized the middle PLCT layer while left the top/bottom BTO cap layers in a poor crystallization status. This sandwiched structure is endowed with an enhanced maximum polarization while a small remnant one, and a much-delayed polarization saturation, which corresponds to a large <em>W</em><sub>rec</sub>~80 J/cm<sup>3</sup> and a high <em>η~</em>86%. Furthermore, the film showed an outstanding cycling-stability: its <em>W</em><sub>rec</sub> and <em>η </em>remain essentially unchanged after 10<sup>9</sup> electric cycles (D<em>W</em>/<em>W<</em>4%, D<em>η</em>/<em>η<</em>2%). These good energy storage characteristics have proved the effectiveness of our proposed strategy, paving a way for the utilization of sandwiched films in applications of electric power systems and advanced pulsed-discharge devices.