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

Highlights: • nBS_xT is prepared for modifying the NBFT–based multilayer thin film by bringing in new interface. • The highest W_rec ~ 56.5 J cm⁻³ and η ~ 66.6% are achieved for the relaxor 7NBFT/3BS_0.15T multilayer structure. • Rayleigh Law is taken to interpret the increased (P_max–P_r) value. • HRTEM is used to confirm the existence of polar nano–regions (PNRs). • The improved homogeneous E_BD and existence of PNRs contribute to the enhanced energy storage performance. Lead–free thin films with excellent high recoverable energy density (W_rec) and efficiency (η) are promising for application in miniature power devices. In this work, Na_0.5Bi_0.5(Ti,Fe)TiO₃ (NBFT) and Ba(Ti,Sr)O₃ (BST) systems are chosen for fabricating a series of 7NBFT/nBS_xT (where 7, n and x mark the spin–coating cycles of NBFT, BS_xT, 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 BS_xT buffer layer on 7NBFT/nBS_xT, including thickness (by modulating number of spin–coating cycles) and Sr²⁺ doping content. The highest W_rec ~ 56.5 J cm⁻³ and η ~ 66.6% are achieved for the relaxor 7NBFT/3BS_0.15T multilayer, which are highly relevant to the enhanced homogeneous breakdown strength (E_BD) of 2814 kV cm⁻¹, large gap between the maximum and remnant polarization (P_max–P_r) of 61.8 μC cm⁻², originated from the highest α_ε and α_εE₀/ε_init 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.