Lead-Free Relaxor Ferroelectric Ceramics with Ultrahigh Energy Storage Densities via Polymorphic Polar Nanoregions Design

One of the long-standing challenges of current lead-free energy storage ceramics for capacitors is how to improve their comprehensive energy storage properties effectively, that is, to achieve a synergistic improvement in the breakdown strength (Eb) and the difference between maximum polarization (Pmax) and remnant polarization (Pr), making them comparable to those of lead-based capacitor materials. Here, a polymorphic polar nanoregions (PNRs) structural design by first introducing 0.06 mol BaTiO3 into Bi0.5Na0.5TiO3 is proposed to construct the morphotropic phase boundary with coexisting structures of micrometer-size domains and polymorphic nanodomains, enhance the electric field-induced polarization response (increase Pmax). Then Sr(Al0.5Ta0.5)O3 (SAT)-doped 0.94 Bi0.5Na0.5TiO3-0.06BaTiO3 (BNBT) energy storage ceramics with polymorphic PNRs structures are synthesized following the guidance of phase-field simulation and rational composition design (decrease Pr). Finally, a large recoverable energy density (Wrec) of 8.33 J cm−3 and a high energy efficiency (η) of 90.8% under 555 kV cm−1 are obtained in the 0.85BNBT-0.15SAT ceramic prepared by repeated rolling process method (enhance Eb), superior to most practical lead-free competitors increased consideration of the stability of temperature (a variation <±6.2%) and frequency (Wrec > 5.0 cm−3, η > 90%) at 400 kV cm−1. This strategy provides a new conception for the design of other-based multifunctional energy storage dielectrics. © 2022 Wiley-VCH GmbH.