High-entropy designed filled tungsten bronze structure ferroelectrics with high Curie temperature and enhanced piezoelectricity

High-entropy design has emerged as a powerful strategy to induce configurational disorder and relaxor behaviour in ferroelectrics; however, its effectiveness in crystallographically constrained systems remains unclear. Here, we address this gap by investigating the filled tungsten bronze ferroelectrics derived from Sr₂KNb₅O₁₅ with multiple cations (Ca²⁺, Sr²⁺, Ba²⁺, Pb²⁺, K⁺ and Na⁺) introduced at A-sites. Single-phase high-entropy ceramics with tetragonal P4bm symmetry are successfully stabilised, exhibiting the increased Curie temperature and improved piezoelectric performance, if compared to the parent compound. Despite the high configurational entropy, the materials display diffuse ferroelectric phase transitions rather than relaxor behaviour. Structural and dielectric analyses reveal that intrinsic A1/A2 site-selective occupation persists, leading to partially ordered local structures and the coexistence of multiple polar states. Ferroelectric measurements further confirm the presence of dual polar states and field-induced transitions, while strain responses indicate the absence of non-180° domain contributions. The enhanced piezoelectric performance associated with high-entropy induced multi-polar configurations exhibits great potential in the applications of ultrasonic detetors. This work provides new insight into the interplay between entropy-driven disorder and site-selective ordering, offering guidance for the design of high-performance ferroelectric materials.