Phase Structures of (K_0.48Na_0.52)_0.945 Li_0.055Sb_0.05Nb_0.95O₃ Piezoceramics

The phase structures of lead-free (K_0.48Na_0.52)_0.945 Li_0.055Sb_0.05Nb_0.95O₃ piezoceramics are studied based on the measurements of ferroelectric and dielectric properties as well as the analyses of x-ray diffraction pattern and energy dispersive spectroscopy. The poled samples exhibit orthorhombic structure whereas the surface and interior for unpoled samples exhibit tetragonal and tetragonal-orthorhombic coexistent structures, respectively. These results are in agreement with the relative permittivity-temperature curves and demonstrate that phase transitions can be induced by Na volatilization and poling process. The remnant polarization P_r measured at 20°C increases continuously with the increase of electric held in the range of 2000–4000 V/mm. This indicates that the polymorphic structure is more beneficial to the rotation or reorientation of dipoles than either the orthorhombic or the tetragonal structure. The randomly oriented domains may be the essential reason for the continuous rotation or reorientation and not good thermal stability.