Realizing ultrahigh recoverable energy density and superior charge–discharge performance in NaNbO3-based lead-free ceramics via a local random field strategy

Abstract

The development and use of high-performance and environmentally friendly energy storage capacitors are urgently demanded. Despite extensive research efforts, the performance of existing lead-free dielectric ceramics is barely satisfactory. In this work, a novel lead-free 0.78NaNbO₃–0.22Bi(Mg_2/3Ta_1/3)O₃ (0.22BMT) linear-like relaxor ferroelectric with ultrahigh energy storage capability and ultrahigh efficiency was designed and synthesized via a local random field strategy. To our satisfaction, an ultrahigh recoverable energy density (W_rec, 5.01 J cm⁻³) and an ultrahigh energy efficiency (η) of 86.1% were achieved simultaneously, which are superior to those of other reported lead-free systems. In addition, excellent temperature, frequency and fatigue stabilities (variation of W_rec < 8% over 20–200 °C, W_rec < 3% after 1–100 Hz and 10⁴ cycles) were observed. More importantly, the 0.22BMT ceramic exhibited a large current density (C_D ∼ 537.9 A cm⁻²), an extremely high power density (P_D ∼ 37.7 MW cm⁻³), and an ultrafast discharge time (t_0.9 ∼ 23 ns). The impedance analysis demonstrated that the introduction of BMT was beneficial for the improvement of the insulation ability and breakdown strength (E_b) of the 0.22BMT ceramic. Additionally, nonisovalent Mg²⁺ and Ta⁵⁺-filled Nb⁵⁺ on the B-site with low average electronegativity generated a random local field, which enhanced the ion bonding, destroyed the long-range order and led to decreased remnant polarization (P_r). These results indicate that this new strategy is a feasible and efficacious means to simultaneously achieve ultrahigh W_rec, superior η and excellent thermal stability in NN-based lead-free ceramics. Furthermore, this work has further broadened the scope of research and the application of the NN-based ceramics.