Achieving ultrastable piezoelectric response over a wide temperature range in BF–BT ceramics via phase-domain-defect regulation

Developing lead-free piezoelectric materials with high thermal stability is essential for sensing and actuation applications in harsh environments. In this work, trace amounts of lithium niobate (LiNbO3) were introduced into the 0.75BiFeO3–0.25BaTiO3 system to tailor the phase structure, lattice distortion, and defect chemistry. The substitution of Li+/Nb5+ for A-/B-site elements promotes partial rhombohedral (R) to tetragonal (T) phase transition, enhances tetragonal distortion, reduces oxygen vacancy formation, and simultaneously strengthens phase separation. This slightly weakens long-range ferroelectric order and facilitates the formation of a suitable amount of nanodomains. The optimized composition (x = 0.001) exhibits highly stable piezoelectric constant (d33) around 107 pC/N (at room temperature) over a broad temperature range of 30–322 °C, with fluctuations below 10%, and retains a high piezoelectric response (d33 ∼ 103 pC/N) even after aging at 300 °C for 12 h. This enhanced stability stems from the balanced interplay among the thermal disturbance de-pinning effect, thermally driven dipole-moment attenuation effect, and thermally induced ferroelectric domain disorder effect. This study offers an effective defect-phase-domain design strategy for realizing lead-free piezoelectric ceramics with high thermal reliability.