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Ferroelectric thin film capacitors with outstanding energy storage performances and fast charge/discharge speed have aroused the attention of researchers due to the development towards the minimization and integration of advanced electronic devices. Herein, environmentally friendly Bi0.2Sr0.7TiO3/BiFeO3 multilayer thin films with different BFO layers have been designed and constructed on Pt(111)/Ti/SiO2/Si substrates by sol–gel/spin coating method. An enhanced polarization and large breakdown strength are simultaneously achieved in the 2BFO multilayer thin film caused by the synergistic effect of multiple polar structures, electric field amplifying effect and interfacial effect, which leads to an ultrahigh energy storage density of ∼50.9 J cm−3 accompanying an efficiency of ∼52.84%. Moreover, the P–E loops of the 2BFO sample are ultra-stable, and no obvious deterioration of the energy storage performances is observed in the wide operating temperature ranges (35–140 °C). The 2BFO capacitor possesses a fast charge/discharge speed of ∼1.5 μs and a giant power density of ∼45.195 MW cm−3, which are superior to that of the commercial BOPP capacitor. The excellent energy storage characteristics make the 2BFO multilayer thin film a promising candidate for energy storage applications. [ABSTRACT FROM AUTHOR]

From the perspectives of environmental protection and health, new lead-free piezoelectric materials have become a research hotspot in the field of materials science. In domain structure engineering, a higher domain wall density stores a higher density of mechanical energy, which is beneficial for the enhancement of piezoelectric properties. Based on this multi-domain structure strategy to improve piezoelectric performance, we introduced BNiT with a multi-domain structure into BNT-based thin films, and constructed (1 − x)(0.94Bi0.5Na0.5TiO3–0.06BaTiO3)–xBi(Ni0.50Ti0.5)O3 (BNT–BT–xBNiT) ternary composite lead-free piezoelectric thin films on Pt(111)/Ti/SiO2/Si(100) substrates via a sol–gel method. Through structural analysis, such as XRD, SEM, Raman and XPS analysis, it was proven that the introduction of BNiT is accompanied by lattice expansion and relaxation characteristics, and the resulting defect dipoles can reduce oxygen vacancies. In particular, the domain structure and phase changes in local regions under different electric fields were characterized by PFM, which proved that the multi-domain structure plays an important role in improving the piezoelectric properties of the thin films. Under the same conditions, the converse piezoelectric coefficient of the BNT–BT–0.02BNiT thin film is about 3.2 times that of the BNT–BT thin film. It is expected that this research can provide a theoretical and experimental basis for the domain structure modification of high-performance lead-free piezoelectric thin films for potential micro-electromechanical system (MEMS) applications. [ABSTRACT FROM AUTHOR]