Structure and Electrical Properties of Lead-Free (Na_0.5K_0.5)NbO₃-BaTiO₃ Ceramics

Abstract

(Na 0.5 K 0.5 )NbO 3 with 0–20 mol% BaTiO 3 has been prepared following the conventional mixed oxide process. High-density samples were obtained through the addition of BaTiO 3 into (Na 0.5 K 0.5 )NbO 3 because of an increase in grain size. X-ray diffraction analysis revealed that, during sintering, all of the BaTiO 3 diffuses into the lattice of (Na 0.5 K 0.5 )NbO 3 to form a solid solution, in which orthorhombic symmetry changes to tetragonal symmetry at x ≈0.06, and tetragonal symmetry changes to cubic symmetry at x =0.20 or higher. It was found that the samples with a low content of BaTiO 3 exhibit relatively good ferroelectric and piezoelectric properties. For 0.98(Na 0.5 K 0.5 )NbO 3 -0.02 BaTiO 3 ceramics, the remanent polarization ( P r ) is 7.5 µC/cm 2 with a coercive field ( E c ) of 12 kV/cm. The piezoelectric constant d 33 reaches 104 pC/N. The electromechanical coupling coefficients of the planar mode k p and the thickness mode k t reach ∼29% and ∼38%, respectively. Our results show that (Na 0.5 K 0.5 )NbO 3 -BaTiO 3 is a good lead-free piezoelectric ceramic.