Dielectric and piezoelectric properties of lead free Na0.5K0.5NbO3-BiScO3 ceramics

A well-known Bi-containing perovskite ferroelectric, BiScO3 (BS), was successfully utilized to develop Na0.5K0.5NbO3 (NKN)-based lead-free piezoelectric ceramics, in which there is a morphotropic phase boundary (MPB) between ferroelectric orthorhombic and rhombohedral phases. The addition of a small amount of BS tends to promote the sinterability of NKN ceramics, and simultaneously, to retard the grain growth, and change the crystalline structures, resulting in a dense (I - x)NKN-xBS solid-solution ceramic upon conventional sintering. Enhanced piezoelectric and electromechanical properties appear near the MPB composition with x = 0.02, the piezoelectric constant being 210 pC/N and the planar electromechanical coupling factor being 45%. This material also has a comparable Curie temperature (340 degrees C to that of commercial Pb(Zr,Ti)O-3 as well. All these results reveal that BS-substituted NKN ceramics may become promising candidates for lead-free piezoelectric materials.