IMPROVED ELECTROMECHANICAL RESPONSE AND RELAXOR FERROELECTRIC BEHAVIOR IN (76–x)Bi₁/₂Na₁/₂TiO₃–24SrTiO₃ CERAMICS MODIFIED WITH BiFeO₃ AND BiAlO₃

Piezoelectric ceramics are smart functional materials capable of converting mechanical energy into electrical energy and vice versa, making them indispensable for modern sensors, transducers, and precision actuators. Historically dominated by lead-containing materials like Pb(Zr,Ti)O₃ (PZT), strict environmental regulations and health concerns have driven an urgent global shift toward eco-friendly alternatives. Currently, bismuth sodium titanate (Bi₁/₂Na₁/₂TiO₃–BNT)-based solid solutions are at the forefront of lead-free piezoceramic trends due to their excellent polarization and electromechanical coupling properties. In this study, lead-free piezoelectric ceramics based on the (76–x)Bi₁/₂Na₁/₂TiO₃–24SrTiO₃ (BNST24) system were synthesized, and their structural, dielectric, and electromechanical properties were systematically investigated. This study compares two modified systems — BiFeO₃ (BFO) and BiAlO₃ (BAO) — focusing on their effects on phase transitions and strain behavior. X-ray diffraction (XRD) confirms a stable perovskite structure with a gradual shift toward pseudocubic symmetry upon doping. Dielectric measurements reveal typical relaxor behavior with clear frequency dispersion. Consequently, the composition-driven ferroelectric-to-relaxor transition leads to a large strain response. At dopant concentrations of 1 mol% for both BFO and BAO, normalized strain coefficients () exceeding 600 pm/V were obtained, indicating strong potential for lead-free actuator applications.