Improved ferroelectric and piezoelectric properties of (Na0.5K0.5)NbO3 ceramics via sintering in low oxygen partial pressure atmosphere and adding LiF

Dense (Na0.5K0.5)NbO3 lead-free ceramics with the simple composition were prepared via sintering in low oxygen partial pressure (pO(2), similar to 10-12 atm) atmosphere and adding LiF. All the ceramics have pure orthorhombic structure. Compared to the LiF-added (Na0.5K0.5)NbO3 ceramics sintered in air and the low pO(2)-sintered pure (Na0.5K0.5)NbO3 ceramics without LiF addition, the present ceramics exhibit improved piezoelectric and ferroelectric properties. The piezoelectric constant d(33) is 125 pC/N, and the converse piezoelectric constant d(33)* is 186 pm/V. The dielectric constant and dielectric loss of the ceramics at room temperature and 1 kHz are 451 and 0.03, respectively. Under the measured electric field of 70 kV/cm, the remanent polarization is 25.9 mu C/cm(2) and the coercive field is 13.9 kV/cm. Furthermore, if the base metals such as Cu and Ni powders were mixed into the green pellets and sintered in the low pO(2) atmosphere, the base metals cannot be oxidized, suggesting possibility of using base metals as electrodes.