Synergistic modulation of lattice distortion and defect dipoles toward high energy storage in Al3+-doped CaBi3LaTi4O15 films under low-to-moderate electric fields

Al 3+ doping realizes controllable lattice distortion and regulated defect dipole construction. • The synergistic effect greatly boosts polarization difference while maintaining excellent relaxor characteristics. • The x  = 0.4 film delivers a superior recoverable energy density of 56 J/cm 3 and a high efficiency of 80% at 1500 kV/cm. • The x  = 0.4 film exhibits excellent thermal stability, favorable frequency stability and ultrafast discharge performance. High-performance lead-free Aurivillius ferroelectric films with superior energy density and fast charge/discharge capability under low-to-moderate electric fields are highly demanded for pulsed power and electronic systems. Herein, CaBi 3 LaTi 4-3 x /4 Al x O 15 films were successfully grown on Pt/Ti/SiO 2 /Si (100) substrates via a sol-gel method. Al 3+ doping introduces controllable lattice distortion and defect dipoles, which synergistically optimize the polarization difference and maintain excellent relaxor behavior in the films. At 1500 kV/cm, the optimal film with x  = 0.4 achieves a prominent W rec $W_{\mathrm{rec}}$ of 56.0 J/cm 3 coupled with an η $\eta$ of 80%, owing to the balanced lattice distortion, an appropriate defect dipole density and suppressed leakage current. Meanwhile, the x  = 0.4 film possesses excellent thermal and frequency stability, as well as an ultrafast discharge response. It also exhibits comparable energy storage capabilities at low-to-medium electric fields relative to previously reported dielectric films. This study provides a reliable pathway to enhance the energy storage performance of bismuth layer-structured ferroelectrics through synergistic modulation of lattice distortion and defect dipoles, which facilitates their practical applications in complex-environment energy storage devices operated at low-to-moderate electric fields.