Microstructure and electrical properties of medium-entropy [Ca_xSr_(1−x)/2Ba_(1−x)/2]Bi₄Ti₄O₁₅ piezoelectric ceramics with a high Curie temperature

Bismuth-layered structure piezoelectric ceramics demonstrate significant potential for high-temperature piezoelectric devices due to their elevated Curie temperature. However, their practical application is constrained by the rapid decline in resistivity at elevated temperatures. In this work, a series of non-equimolar medium-entropy piezoelectric ceramics Ca_xSr_(1-x)/2Ba_(1-x)/2Bi₄Ti₄O₁₅ were synthesized via conventional solid-state methods, with systematic investigation of configurational entropy effects on microstructure and electrical properties. Results indicate the successful formation of pure Aurivillius phase across all compositions. Comprehensive characterization through X-ray diffraction and complementary techniques reveals the presence of disordered structures and diverse lattice distortions. Notably, the medium-entropy design-induced diffusion retardation effect significantly enhances grain boundary density, thus hindering electronic charge transport while beneficially enhancing resistivity. These structural modifications synergistically improve electrical characteristics. The Ca_0.2Sr_0.4Ba_0.4Bi₄Ti₄O₁₅ composition achieves remarkable performance metrics with enhanced resistivity (2.4 × 10⁷ Ω cm) at 500 °C and substantial piezoelectric coefficient (14 pC/N). This work establishes a strategic paradigm for developing high-performance piezoelectric ceramics.