Proved phase fraction effect within MPB composition for high electromechanical properties in lead-free BF-BT ceramics

Finding alternative to lead-based piezoelectric materials is crucial due to environmental concerns. To optimize the morphotropic phase boundary (MPB) effect in BiFeO₃-based lead-free piezoelectric materials, eco-friendly lead-free (BiFeO₃)_1-x(BaTiO₃)_x (BF-BT) ceramics were synthesized using the conventional solid-state reaction method followed by an air-quenching process. Their structural, ferroelectric, piezoelectric and dielectric behaviors were investigated. X-ray diffraction patterns revealed a single-phase perovskite structure with an MPB between rhombohedral and tetragonal phases. BF-35BT ceramics exhibited high maximum polarization (P_max = 30.16 µC/cm²) and remnant polarization (P_r = 21.29 µC/cm²) with a minimum coercive field at room temperature, which further improved to 48.55 µC/cm² and 44.14 µC/cm² at high temperature (125 °C). A maximum unipolar strain of 0.20% with corresponding dynamic piezoelectric coefficients (d33∗= 406 pm/V) was achieved at x = 0.35, while x = 0.33 composition exhibited a high static piezoelectric coefficient (d₃₃ = 218pC/N). This study identifies MPB, high relative density, optimum average grain size, and maximum lattice distortion as key factors enhancing electromechanical properties. Among these parameters, the role of phase fraction (which maximizes configurational entropy) in the MPB composition significantly improves electromechanical properties. These results clearly demonstrate the mechanism behind the domain configuration changes related to the MPB effect, offering a pathway for the commercial use of BF-BT-based lead-free ceramics.