High-Entropy Strategy for Improved Mechanical and Energy Storage Properties in BaTiO₃-BiFeO₃-Based Ceramics

Dielectric capacitors are employed extensively due to their exceptional performance, including a rapid charge-discharge speed and superior power density. However, their practical implementation is hindered by constraints in energy-storage density (ESD), efficiency (ESE), and thermal stability. To achieve domain engineering and improved relaxor behavior in 0.67BiFeO₃-0.33BaTiO₃-based Pb-free ceramics, the concerns have been addressed here by employing a synergistic high-entropy strategy involving the design of the composition of Sr(Mg_1/6Zn_1/6Ta_1/3Nb_1/3)O₃ with B-site multielement coexistence and high configuration entropy. Remarkably, in (0.67-x)BiFeO₃-0.33BaTiO₃-xSr(Mg_1/6Zn_1/6Ta_1/3Nb_1/3)O₃ ceramics with x = 0.08, a good ESE (η) of 75% and a recoverable ESD (W_rec) of 2.4 J/cm³ at 190 kV/cm were attained together with an ultrahigh hardness of ∼7.2 GPa. The high-entropy strategy, which is tailored by an increase in configuration entropy, can be attributed to the superior mechanical and ES properties. It also explains the enhanced random field and relaxation behavior, the structural coexistence of ferroelectric rhombohedral (R3c) and nonpolar pseudocubic (Pm-3m) symmetries, the decreased domain size, and evenly distributed polar nanoregions (PNRs). Moreover, improved thermal stability and outstanding frequency stability are also obtained. By boosting the configuration entropy, BiFeO₃-BaTiO₃ materials dramatically improved their complete energy storage performance. This suggests that designing high-performance dielectrics with high entropy can be a convenient yet effective technique, leading to the development of advanced capacitors.