High entropy engineering has emerged as a new strategy to improve the energy storage density and efficiency of dielectric capacitors due to its unique design concept. However, the recyclable energy storage density (W_rec) reported so far has never exceeded 2 J/cm³ for the type of high-entropy ceramics with equimolar elements occupying A or B site. In order to improve this type high-entropy ceramics. Na_0.5Bi_0.5TiO₃ (NBT) was used as the matrix, equimolar Sr²⁺, La³⁺, K⁺ and Ba²⁺ were gradually introduced into at the A-site of the matrix lattice to increase configurational entropy. The results show that the relaxor degree, band gap width, interfacial polarization, and breakdown field strength are effectively improved with increasing entropy. Among them, suppressing interfacial polarization is an important factor to increase the breakdown field strength and thus enhance the energy storage performance. The (Na_1/6Bi_1/6Sr_1/6La_1/6K_1/6Ba_1/6)TiO₃ (NBSLKBT) sample with the highest configurational entropy shows an ultra-high W_rec of 9.8 J/cm³ and the energy storage efficiency (η = 86.5%). This work demonstrates that entropy strategy for superior energy-storage performance still works on the above type high-entropy ceramics and opens up a new way of modulating interface polarization by entropy increase strategy.

Bismuth ferrite–based ferroelectric ceramics are considered strong competitors in high–temperature piezoelectric applications that benefits from their high depolarization temperature (T_d), but problems of large conductivity and low piezoelectric coefficient (d₃₃) should be tackled. BiFeO₃–PbTiO₃–x(Sr_0.7Bi_0.2□_0.1)TiO₃ (BF–PT–xSBT) ternary system are designed in this work that successfully resolves this tough paradox. Rietveld refinements show that this system exhibits multiphase coexistence with complex structural transition among rhombohedral, tetragonal and pseudocubic phase. Interestingly, a high T_d ~320 ℃ and d₃₃ ~ 236 pC/N are synergistically optimized in x=0.20 composition near pseudo–phase boundary, which are indicated by multi–scale techniques (phase structure, dielectric analysis etc.). What's more, dual electrostrain peaks appear at separate phase boundaries for x=0.20 and 0.66 compositions with distinct piezo/ferroelectric properties. Rayleigh law and piezoelectric force microscopy analysis clarify that the optimal electrostrain performance for both critical compositions are dominated by intrinsic (x=0.20) and extrinsic (x=0.66) contributions, respectively. This work not only provides a new BF–PT–xSBT system with a high T_d and superior d₃₃ that are promising candidates in high–temperature actuator and sensor applications, but also presents a possibility of multiphase–coexistence established exotic macroscopic performances.