Ultrahigh energy density in short-range tilted NBT-based lead-free multilayer ceramic capacitors by nanodomain percolation

Dense pseudocubic 0.62Na_0.5Bi_0.5TiO₃-0.3Sr_0.7Bi_0.2TiO₃-0.08BiMg_2/3Nb_1/3O₃ (NBT-SBT-0.08BMN) ceramics with excellent recoverable energy density, W_rec = 7.5 J/cm³, and conversion efficiency, η = 92%, were synthesized. Large electric breakdown strength was facilitated by electrical homogeneity, high resistivity and large activation energy (1.86 eV). Transmission electron microscopy identified the presence of polar nano-regions (PNRs) in a matrix of short coherence in-phase and antiphase octahedral tilting. Combining polar and tilt order restricted the crystal classes of PNRs to tetragonal, orthorhombic and monoclinic. Using these symmetries, the enhancement of polarization was explained using Landau-Devonshire phenomenology and percolation theory. Octahedral tilting and introduction of larger B-site ions (Mg²⁺, Nb⁵⁺) inhibited long range polar coupling, minimizing strain and maximizing η. W_rec was further improved to 18 J/cm³ (>1000 kV/cm) in multilayers whose properties were stable from 0.01–100 Hz, from 20°C–160°C and up to 10⁶ cycles, attractive for pulsed power applications and power electronics.