The construction of relaxor perovskite Na0.5Bi0.5(Fe0.03Ti0.97)O3/Ba(Ti1-xSrx)O3 multilayer thin film and explorations on origin of the enhanced energy storage performance

Lead–free thin films with excellent high recoverable energy density (Wrec) and efficiency (η) are promising for application in miniature power devices. In this work, Na0.5Bi0.5(Ti,Fe)TiO3 (NBFT) and Ba(Ti,Sr)O3 (BST) systems are chosen for fabricating a series of 7NBFT/nBSxT (where 7, n and x mark the spin–coating cycles of NBFT, BSxT, and Sr2+ doping content, respectively) (n = 0, 2, 3, 4, and x = 0, 5, 10, 15, 20 mol. %) multilayer structures on Pt/Ti/SiO2/Si substrates via sol–gel process to explore the effects from key parameters of BSxT buffer layer on 7NBFT/nBSxT, including thickness (by modulating number of spin–coating cycles) and Sr2+ doping content. The highest Wrec ~ 56.5 J cm−3 and η ~ 66.6% are achieved for the relaxor 7NBFT/3BS0.15T multilayer, which are highly relevant to the enhanced homogeneous breakdown strength (EBD) of 2814 kV cm−1, large gap between the maximum and remnant polarization (Pmax–Pr) of 61.8 μC cm−2, originated from the highest αe and αeE0/einit values as interpreted according to the Rayleigh Law. Besides, the existence of polar nano–regions (PNRs) contributes by lowering the energy for domain back–switching. These provide evidence that NBT–based multilayer thin film is of considerable potential for lead–free energy storage application.