Phase structures and electrical properties of new lead-free (Na0.5K0.5)NbO3-(Bi0.5Na0.5)TiO3 ceramics

Highly dense (1-x)(Na0.5K0.5)NbO3-x(Bi0.5Na0.5)TiO3 (NKN-BST) solid solution piezoelectric ceramics have been fabricated by ordinary sintering. All compositions show pure perovskite structures, showing room-temperature symmetries of orthorhombic at x <= 0.02, of tetragonal at 0.03 <= x <= 0.09, of cubic at 0.09 < x <= 0.20, and of rhombohedral at x > 0.20. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal ferroelectric phases was identified in the composition range of 0.02 < x < 0.03. The materials near the MPB exhibit a strong compositional dependence, owning peak values of the planar electromechanical coupling factor k(p)similar to 43%, the piezoelectric constant d(33)similar to 195 pC/N, and the Curie temperature of 375 degrees C comparable to that of commercial lead zinconate titanate ceramics. The results indicate that NKN-BST ceramic is a promising lead-free piezoelectric candidate material. (c) 2007 American Institute of Physics.