Review on performance optimization strategies and their mechanisms of bismuth layered-structured piezoelectric ceramics

Bismuth layered-structured ferroelectrics (BLSFs) possess an exceptionally ultra-high intrinsic Curie temperature (generally above 600 ^\circC) and excellent thermal stability, making them indispensable in high-temperature applications such as aerospace and nuclear power generation. However, the commonly prepared BLSF ceramics have low piezoelectric activity (d_33 < 10 pC/N) and a high coercive field. This performance limitation originates from the spatial confinement of spontaneous polarization imposed by the two-dimensional layered structure as well as the oxygen vacancy defects introduced by bismuth volatilization during high-temperature sintering. This paper systematically reviews the recent research progress on the optimization method for the piezoelectric performance of BLSFs: 1) multi-element doping (A-site, B-site, A/B-site doping), which achieves a synergistic enhancement of piezoelectric response and intrinsic thermal stability by regulating the degree of lattice distortion, inhibiting oxygen vacancy migration, and inducing the formation of pseudo-tetragonal phase boundaries; 2) texturing processes including templated grain growth and hot pressing sintering achieve the statistical average limits of polycrystals by inducing oriented grain arrangement, resulting in anisotropic piezoelectric properties approaching those of single crystals; 3) high-entropy material design, which breaks the traditional constraint of polarization being confined to the a-b plane by introducing multi-principal elements to form two-dimensional amorphous defect layers, leading to additional out-of-plane polarization components and achieving a breakthrough in polarization flexibility and comprehensive performance. By analyzing the structural modification mechanisms of different systems, this paper reveals the synergistic enhancement effects of lattice distortion regulation, oxygen vacancy suppression, domain engineering, and high-entropy design on piezoelectric performance. This paper aims to provide strategic references for the rational design of high-performance high-temperature piezoelectric materials. Finally, it presents prospects for the piezoelectric performance and future applications of bismuth layer-structured piezoelectric ceramics.