Time-dependent polarization behavior and energy storage performance of (1−x)Na0.5Bi0.5(Fe0.03Ti0.97)O3-xSrTiO3 thin films via aging control

The aging process is intrinsically linked to the polarization dynamics of relaxor ferroelectrics, by which their energy storage performance can be modulated. In this work, (1x)Na_0.5Bi_0.5(Fe_0.03Ti_0.97)O₃-xSrTiO₃ ((1−x)NBFT-xSTO, x = 0, 0.0025, 0.05, 0.1) thin films are fabricated on Ni–Cr foil via sol–gel method. To investigate the mechanisms of polarization dynamics of (1−x)NBFT-xSTO during aging, we analyze the effects of crystallinity, polarization, and related energy storage properties at different aging durations for revealing time-dependent characteristics. The 0.9NBFT-0.1STO thin film exhibits superior anti-aging stability, with negligible variation in both polarization–electric field hysteresis (P-E) loops and energy storage performance after aged ~ 60 d. The 0.95NBFT-0.05STO thin film exhibits a ~ 34% reduction in recoverable energy density (W_rec) after ~ 60 days of aging, while it still maintains a higher W_rec compared to other thin films. The energy storage efficiency (η) is increased by ~ 36%, achieving W_rec ~ 44.3 J/cm³ and η ~ 45% at 20 kHz. Moreover, 0.95NBFT-0.05STO and 0.9NBFT-0.1STO exhibit low-frequency dependence in their fresh state, which disappears after aging. This is attributed to the increased inhibition electric field (E_d) generated by defect dipoles during aging, which reduces the overall polarization response. Simultaneously, the elevated E_d suppresses the polarization switching, thereby yielding a lower remnant polarization (P_r). This phenomenon further demonstrates that aging is not entirely a detrimental effect for relaxor ferroelectrics, but can be utilized as a tool for modulating energy storage performance.