Boosting energy storage at moderate fields in Sr₀.₇Bi₀.₂TiO₃ weakly polar relaxor via BiNi2/3Ta1/3O₃-induced ferroelectric-paraelectric composite structure

The weakly polar relaxor Sr₀.₇Bi₀.₂TiO₃ is renowned for its exceptional energy efficiency but suffers from low maximum polarization. To overcome this trade-off, we introduce BiNi 2/3 Ta 1/3 O₃ to design a composite structure of coexisting ferroelectric A 4 B 3 O 12 and paraelectric ABO₃ phases. With increasing dopant, the A 4 B 3 O 12 phase is progressively replaced by paraelectric ABO₃ and pyrochlore Bi 2 Ti 2 O 7 , raising the phase-transition temperature. The optimal composition comprises 70.67% P 4/ mbm ABO₃, 28.49% Fmmm A 4 B 3 O 12 , 0.75% Fd 3 m Bi 2 Ti 2 O 7 , and 0.09% Pnna BiTaO 4 , forming polar clusters and a coherent boundary between the ABO₃ and A 4 B 3 O 12 phases. This yields a high energy storage density of 5.12 J cm -3 an ultrahigh efficiency of 97.13% at a high breakdown strength of 460 kV cm -1 , together with a figure of merit of 175.90 J cm -3 and environment-independent stability. These results establish the composite as a highly promising candidate for high-performance dielectric energy-storage devices.