Synergistic Regulation of Piezoelectric-Pyroelectric Multifunctionality in Bi _0.5 Na _0.5 TiO ₃ (BNT) Ceramics via High-Entropy Engineering

As a representative lead-free perovskite compound, Bi_0.5Na_0.5TiO₃ (BNT) is widely recognized as a promising candidate for advanced piezoelectric and pyroelectric ceramics, which is primarily attributed to its relatively high Curie temperature, substantial spontaneous polarization and the intrinsic environmental compatibility. However, further improvement in piezoelectric and pyroelectric properties is critically hindered by its low depolarization temperature (<i>T</i>_d), which limits the reliable operation under high-temperature conditions. In this study, the high-entropy engineering was adopted to construct a (1-<i>x</i>)Bi_0.5Na_0.5TiO₃-<i>x</i>(Bi_1/6Na_1/6Ba_1/6Sr_1/6Mg_1/6Zn_1/6TiO₃) ceramic system. By introducing A-site multicomponent configurations, lattice distortion and local disorder were effectively modulated, accompanied by a synergistic enhancement of polarization thermal stability and pyroelectric response. Particularly, the sample of <i>x</i> = 0.15 presented an enhanced polarization stability, with maintaining the piezoelectric coefficient d₃₃ of ∼80 pC/N, increasing <i>T</i>_d to 182 °C and obtaining the high mechanical quality factor Q_m of 1036. Meanwhile, the sample of <i>x</i> = 0.05 exhibited the optimal pyroelectric performance, with <i>T</i>_d = 176 °C, <i>F</i>_<i>v</i> = 3.24 × 10^-2 m²/C and the piezoelectric activity quality factor of 1658 × 10^-15 m²/N. These results demonstrate that high-entropy engineering can effectively overcome the trade-offs in conventional doping, to synergistically improve the piezoelectric and pyroelectric responses. These results also provide an effective strategy for the development of lead-free multifunctional ceramics applied under high-temperature condition.