Non-equimolar bismuth-layered [Ca_xSr_(1–x)/3Ba_(1–x)/3Pb_(1–x)/3]Bi₄Ti₄O₁₅ high-entropy ceramics with high curie temperature

Aurivillius phase ceramics exhibit significant potential in high-temperature piezoelectric devices due to their high Curie temperature. However, the rapid decrease in electrical resistivity at high temperatures limits their application. In this work, a series of non-equimolar high-entropy piezoelectric ceramics [Ca_xSr_(1–x)/3Ba_(1–x)/3Pb_(1–x)/3]Bi₄Ti₄O₁₅ were designed and prepared via a conventional solid-state method, and the influence of configurational entropy on the microstructure and electrical properties was investigated. The results show that the pure Aurivillius phase was obtained for all compositions. Due to the hysteretic diffusion effect caused by high entropy design, the grain boundary density is effectively increased, leading to a degradation of electrical transport properties. The results of Raman and TEM indicate that disordered structure and various lattice distortions such as edge dislocations, twists, and tilts of oxygen octahedra coexist in high-entropy ceramics, which synergistically contribute to the increase in ceramic electrical resistivity. Consequently, the electrical resistivity at 500 °C increased by 1–2 orders of magnitude, the sample with x = 0.4 exhibits high electrical resistivity (1.18 × 10⁸ Ω·cm), and also boasts a high piezoelectric coefficient (14 pC/N) and an optimal operating temperature (>550 °C). This work highlights a way to obtain high-performance piezoelectric ceramics with high Curie temperature through the non-equimolar high-entropy composition design.