High energy-storage density under low electric field in (Na0.5Bi0.5)TiO3-SrTiO3 ferroelectric thin films through multi-element B-site substitutions

Large discrepancy between maximum polarization and remanent polarization ΔP (P_max-P_r) and high breakdown strength (E_b) are the two decisive parameters to achieve outstanding energy storage performance in dielectric capacitors. However, high voltage (3–6 MV cm⁻¹) often generates heat generation and unexpected insulation failures, greatly deteriorating both device stability and service lifetime. Herein, we propose an approach on boosting up ΔP of (Na_0·5Bi_0.5)_0.65Sr_0·35Ti_0.99-xMn_0.01Nb_xO₃-SrTiO₃ (NBSTMn-xNb) films to realize high energy storage density (W_rec) at low electric field by introducing $\left[{\text{Mn}}_{\text{Ti}}^{″}-V_o^{··}\right]$ defect dipoles and Mn³⁺-Nb⁵⁺ ionic pairs. The synergistic effect of $\left[{\text{Mn}}_{\text{Ti}}^{″}-V_o^{··}\right]$ defect dipoles enabled reversible domain switching and Mn³⁺-Nb⁵⁺ ionic pairs caused chemical pressure and coupled the inherent ferroelectric instability, yielding a huge ΔP of 78.7 μC/cm² at 1790 kV/cm. Consequently, an energy density of 48.03 J/cm³ with an efficiency of 67.7 % at a low electric field of 1790 kV/cm was realized in NBSTMn-xNb (x = 1.0 %) film. Besides, the NBSTMn-1.0 %Nb film also exhibits excellent stability in frequency (0.2–10 kHz) and temperature (20–200 C) under 1000 kV/cm. These findings present an opportunity to develop high energy density thin film capacitors at low electric field strength though introducing composite dipoles.