Outstanding Energy Storage Performance in High‐Hardness (Bi0.5K0.5)TiO3‐Based Lead‐Free Relaxors via Multi‐Scale Synergistic Design

Abstract

AbstractLead‐free dielectric ceramics with ultrahigh energy storage performance are the best potential stocks used in next‐generation advanced pulse power capacitors. Here, an ultrahigh recoverable energy storage density Wrec of ≈7.57 J cm−3 and a large efficiency η of ≈81.4% are first realized in (Bi0.5K0.5)TiO3 (BKT)‐based relaxor ferroelectric ceramics with an ultrahigh Vickers hardness Hv ≈ 8.63 Gpa by adding BaTiO3 and NaNbO3 in order to synergistically design the domain and microstructure in multiscale, leading to the existence of ultrasmall polar nanoregions, ultrafine grain size, compact grain boundaries, dense microstructure, and large band gap Eg simultaneously. Encouragingly, an excellent energy storage temperature stability (Wrec ≈ 4.31 ± 0.25 J cm−3, η ≈ 86 ± 5%, 20–200 °C), frequency stability (Wrec ≈ 5.14 ± 0.12 J cm−3, η ≈ 81.3 ± 1.2%, 5–100 Hz), and excellent charge/discharge performance (power density PD ≈ 103.2 MW cm−3, discharge energy density WD ≈ 2.4 J cm−3, discharge rate t0.9 ≈ 130 ns) are also achieved in BKT‐based ceramics. The results demonstrate that BKT‐based ceramics can be very competitive lead‐free relaxors for energy storage capacitors in pulsed power devices.