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 (E b ) and the difference between maximum polarization (P max ) and remnant polarization (P r ), making them comparable to those of lead-based capacitor materials. Here, a polymorphic polar nanoregions (PNRs) structural design by first introducing 0.06 mol BaTiO 3 into Bi 0.5 Na 0.5 TiO 3 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 P max ). Then Sr(Al 0.5 Ta 0.5 )O 3 (SAT)-doped 0.94 Bi 0.5 Na 0.5 TiO 3 -0.06BaTiO 3 (BNBT) energy storage ceramics with polymorphic PNRs structures are synthesized following the guidance of phase-field simulation and rational composition design (decrease P r ). Finally, a large recoverable energy density (W rec ) 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 E b ), superior to most practical lead-free competitors increased consideration of the stability of temperature (a variation <±6.2%) and frequency (W rec > 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.