Outstanding energy density and hardness in Ba_0.85 Ca_0.15 Zr_0.1 Ti_0.9 O₃ -based ceramics via weakly coupled relaxor design

Lead-free ceramic-based dielectric capacitors demonstrate significant potential for pulse power energy storage applications due to their high power density and rapid charge/discharge characteristics. In this study, highly dynamic polar nanoregions (PNRs) were constructed in (1 − x)[0.92Ba_0.85 Ca_0.15 Zr_0.1 Ti_0.9 O₃ –0.08Bi(Zn_2/3 Ta_1/3)O₃]-xBi_0.5 Na_0.5 TiO₃ (abbreviated as BNTx) dielectric ceramics by introducing the strongly polar relaxor end-member Bi_0.5 Na_0.5 TiO₃ (BNT). Meanwhile, the hybridization of Bi 6s and O 2p orbitals improves the polarization capability of the ceramics, resulting in a larger polarization difference (ΔP ∼47.8 μC cm⁻²). Furthermore, due to the high doping concentration of BNT and Ta donor doping, BNTx relaxor ferroelectrics exhibit high bulk resistivity, submicron grain size (∼0.57 μm), and wide bandgap characteristics, leading to a remarkable improvement in breakdown strength (E_b ∼710 kV cm⁻¹). Both the electroactive regions corresponding to the bulk and grain boundaries showed similar characteristics, indicating a homogeneous electrical microstructure and intrinsic resistance which significantly contributed to maintaining the high resistivity of the samples. Through compositional optimization, the 20% BNT-doped BCZT-based relaxor ferroelectric ceramic (BNT20) achieves a Vickers hardness of ∼8.608 GPa while demonstrating exceptional energy storage performance, including an outstanding recoverable energy density (W_rec) of ∼10.6 J cm⁻³ and ultrahigh energy efficiency (η) of ∼87%. Notably, the stable PNRs significantly improved the temperature and frequency stability of the dielectric constant and energy storage performance. Furthermore, the BNT20 ceramic exhibits a high current density (C_D ∼1108.3 A cm⁻²), power density (P_D ∼132.99 MW cm⁻³), and an ultrafast discharge speed (t_0.9 ∼79.9 ns), demonstrating its promising application prospects in pulse power systems.