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Dense ( Na 0. 5 K 0. 5) NbO3 lead-free ceramics with the simple composition were prepared via sintering in low oxygen partial pressure (pO2, ∼ 10 − 1 2 atm) atmosphere and adding LiF. All the ceramics have pure orthorhombic structure. Compared to the LiF-added ( Na 0. 5 K 0. 5) NbO3 ceramics sintered in air and the low pO2-sintered pure ( Na 0. 5 K 0. 5) NbO3 ceramics without LiF addition, the present ceramics exhibit improved piezoelectric and ferroelectric properties. The piezoelectric constant d 3 3 is 125 pC/N, and the converse piezoelectric constant d 3 3 * 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 μ C/cm2 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 pO2 atmosphere, the base metals cannot be oxidized, suggesting possibility of using base metals as electrodes. [ABSTRACT FROM AUTHOR]