The development of environmentally friendly energy storage dielectrics with high energy storage density has attracted increasing attention in power electronics. The combination of antiferroelectric ceramics with relaxor characteristics proves to be an efficient way to greatly improve energy storage properties. In this work, a novel (Na1-x/2Lax/2)(Nb1-xTix)O3 lead-free bulk ceramic exhibits excellent energy storage properties of a giant recoverable energy storage density Wrec ≈ 6.5 J/cm3, a relatively high efficiency η ≈ 66%, and an ultrafast discharge speed t0.9 ≈ 50 ns at x = 0.18, showing outstanding potential for pulsed power capacitors. The Rietveld structural refinement and Raman spectra suggest a relaxor antiferroelectric orthorhombic R phase at room temperature as x > 0.16. Obviously enhanced breakdown strength can be ascribed to ultrafine grains of ∼0.21 μm and largely improved resistivity after BaCu(B2O5) doping. The detailed analysis of high-resolution transmission electron microscopy and in situ field Raman spectra clearly discloses the existence and rapid response feature of antipolar nanoregions and the resulting high driving field (∼30 kV/mm) for the antiferroelectric-to-ferroelectric phase transition, laying a solid foundation for the achievement of desirable energy storage characteristics. These results would provide a reliable strategy and a good understanding for designing new energy storage capacitor dielectrics.
Keywords: NaNbO3; breakdown strength; energy storage; lead free; relaxor antiferroelectric.