Synergically improved energy storage performance and stability in sol–gel processed BaTiO3/(Pb,La,Ca)TiO3/BaTiO3 tri-layer films with a crystalline engineered sandwich structure

Abstract

Achieving an excellent energy storage performance, together with high cycling reliability, is desirable for expanding technological applications of ferroelectric dielectrics. However, in well-crystallized ferroelectric materials, 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 (Wrec) and efficiency (η). Nanocrystalline ferroelectric films with a macroscopically amorphous structure have shown an improved Wrec and η, but their much lower polarizability demands an extremely high electric field to achieve such performances, which is undesirable from an economic viewpoint. Here, we propose a strategy to boost the energy storage performances and stability 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 BaTiO3/(Pb,La,Ca)TiO3/BaTiO3 (BTO/PLCT/BTO) tri-layer films, we show that the above design is realized via 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 large Wrec ≈ 80 J/cm3 and high η ≈ 86%. Furthermore, the film showed an outstanding cycling stability: its Wrec and η remain essentially unchanged after 109 electric cycles (ΔW/W < 4%, Δη/η < 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.

Keywords

• energy storage
• sandwich film
• amorphous structure
• nanocrystal cluster
• stability