Study of the relationships among the crystal structure, phase transition behavior and macroscopic properties of modified (K,Na)NbO3-based lead-free piezoceramics

Although phase boundary engineering has made notable progress in improving the electrical properties of (K,Na)NbO3-based piezoceramics, lattice distortion and spontaneous polarization of multiphase coexisting systems are a few of the remaining concerns. Here, new research employing XRD Rietveld refinement was performed to explore crystal structures, phase fractions and atomic parameters of Fe2O3-added (0.995-x)K0.48Na0.52NbO3-xBi0.5Na0.5ZrO3-0.005BiScO3 ceramics. The distortion of the oxygen octahedron and the spontaneous polarization were presented. Central cation displacement provides a much larger contribution to polarization and the electric dipole moment in orthorhombic phase is much larger than that in tetragonal phase. Benefiting from tetragonal-orthorhombic phase coexistence and lattice distortion, optimized ferroelectric and piezoelectric properties (d33 ∼ 381 pC/N, Pr ∼ 20.47 μC/cm2) were obtained. The ceramic still holds a large d33 (313 pC/N) after up to 300 ℃ of thermal annealing. A series of material constants was also calculated and compared to lead-based ones.