Structure and electrical properties of lead-free (Na0.5K0.5)Nbo3-BaTiO3 ceramics

(Na0.5K0.5)NbO3 with 0-20mol% BaTiO3 has been prepared following the conventional mixed oxide process. High-density samples were obtained through the addition of BaTiO3 into (Na0.5K0.5)NbO3 because of an increase in grain size. X-ray diffraction analysis revealed that, during sintering, all of the BaTiO3 diffuses into. the lattice of (Na0.5K0.5)NbO3 to form a solid solution, in which orthorhombic symmetry changes to tetragonal symmetry at x approximate to 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 BaTiO3 exhibit relatively good ferroelectric and piezoelectric properties. For 0.98(Na0.5K0.5)NbO3-0.02 BaTiO3 ceramics, the remanent polarization (P-r) is 7.5 muC/cm(2) with a coercive field (E-c) of 12 kV/cm. The piezoelectric constant d(33) reaches 10(4) pC/N. The electromechanical coupling coefficients of the planar mode k(p) and the thickness mode k(t) reach similar to29% and similar to38%, respectively. Our results show that (Na0.5K0.5)NbO3-BaTiO3 is a good lead-free piezoelectric ceramic.