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

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 0.78NaNbO(3)-0.22Bi(Mg2/3Ta1/3)O-3 (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 (eta) 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 degrees C, W-rec < 3% after 1-100 Hz and 10(4) cycles) were observed. More importantly, the 0.22BMT ceramic exhibited a large current density (C-D similar to 537.9 A cm(-2)), an extremely high power density (P-D similar to 37.7 MW cm(-3)), and an ultrafast discharge time (t(0.9) similar to 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 eta 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.