Physical and Electrical Properties of Lead-Free (Bi_0.5Na_0.5)TiO₃-(Na_0.5K_0.5)NbO₃ Ceramics

Abstract

Lead-free (1- x )(Bi 0.5 Na 0.5 )TiO 3 – x (Na 0.5 K 0.5 )NbO 3 ( x <0.1) ceramics have been prepared by the conventional mixed oxide process. X-ray diffraction analysis revealed that, during sintering, all of the (Na 0.5 K 0.5 )NbO 3 diffuse into the lattice of (Bi 0.5 Na 0.5 )TiO 3 to form a solid solution and the hexagonal phase with a perovskite structure. The samples with a low content of (Na 0.5 K 0.5 ) NbO 3 exhibit relatively good physical and electrical properties. For 0.96(Bi 0.5 Na 0.5 ) TiO 3 –0.04 (Na 0.5 K 0.5 ) NbO 3 ceramics, the electromechanical coupling coefficients of the planar mode k p and the thickness mode k t reach 0.25 and 0.52, respectively, after sintering at 1100 °C for 5 h. The ratio of the thickness coupling coefficient to the planar coupling coefficient is 2.08. With suitable (Na 0.5 K 0.5 )NbO 3 concentration and sintering conditions, a dense microstructure and good electrical properties are obtained. Our results show that 0.96(Bi 0.5 Na 0.5 )TiO 3 –0.04(Na 0.5 K 0.5 )NbO 3 solid solution ceramics are promising lead-free ceramics for high-frequency electromechanical transducer applications.