Structures and piezoelectric properties of (NaKLi)1−x(BiNaBa)xNb1−xTixO3 lead-free ceramics

Lead-free solid solution piezoelectric ceramics (1−x)(Na0.475K0.475Li0.05)NbO3–x(Bi0.48Na0.48Ba0.04)TiO3 (x=0–0.15) have been fabricated by traditional solid state sintering. All compositions studied have pure perovskite structures, showing an orthorhombic-tetragonal phase transition with increasing x. The tetragonality, however, declined with further increasing x. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal ferroelectric phases was identified approximately at x=0.02, leading to enhanced electrical properties of the dielectric constant εr∕εo∼702, the piezoelectric constant d33∼328pC∕N, and the planar electromechanical coupling factor kp ∼48%. The MPB composition has a higher Curie temperature (415°C) than most Pb(Zr,Ti)O3 compositions. These solid solution ceramics look promising as potential lead-free candidate materials.