Modulation of capacitive energy storage performance in 0.9(Na0.5Bi0.5)(Fe0.02Ti0.98)O3-0.1SrTiO3 relaxor ferroelectric thin film via sol-gel optimizing strategy

0.9(Na0.5Bi0.5)(Fe0.02Ti0.98)O3-0.1SrTiO3 (NBSFT) precursor solutions with varying ratios (1:0, 2:1, 1:1 and 1:2) of C2H6O2 to C3H8O2 are modulated and phase-pure thin films (marked as NBSFT10, NBSFT21, NBSFT11 and NBSFT12) are deposited onto Pt(111)/Ti/SiO2/Si substrate. The hydrolysis of titanate is enhanced with the addition of C3H8O2, which is beneficial for the formation of three-dimension network structure in the sol-gel. The wettability of sol-gel onto the substrate is improved and both the critical radius of new phase and phase transition energy barrier from liquid to solid phases are decreased. All these contribute to fine grain size, even and dense microstructure, and smooth surface for thin films. Besides, the low phase transition energy barrier causes the ion migration with high-efficiency and the increased degree of ion disorder, which is highly relevant to the relaxation behavior of the thin films. Note that the NBSFT11 thin film possesses higher recoverable energy storage density (Wrec) and efficiency (η) of 41.0 J/cm3 and 71.6%, respectively under 3207.6 kV/cm. Excellent thermal stability within the temperature range of 20–220 °C, frequency stability in the range of 1–20 kHz, and fatigue resistance up to 1 × 108 cycles are obtained. These findings provide a novel approach and valuable guidance for designing ferroelectric thin films for energy storage applications.