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-xBi(0.5)Na(0.5)ZrO(3)-0.005BiScO(3) 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 (d(33) similar to 381 pC/N, P-r similar to 20.47 mu C/cm(2)) were obtained. The ceramic still holds a large d(33) (313 pC/N) after up to 300 degrees C of thermal annealing. A series of material constants was also calculated and compared to lead-based ones.