(Na0.5K0.5)NbO3-LiTaO3 lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics were prepared in the system (1−x)(Na0.5K0.5)NbO3-xLiTaO3 following the conventional mixed oxide route. The effect of cationic substitution of lithium for sodium and potassium in the A sites and tantalum for niobite in the B sites in (Na0.5K0.5)NbO3 (NKN) perovskite lattice on symmetry and physical properties were investigated. The materials with perovskite structure are in orthorhombic phase when x<5 mol.% and transform to tetragonal phase when x>6 mol.%; when x≥8 mol.%, a K3Li2Nb5O15 phase with tetragonal tungsten bronze structure begins to appear and becomes dominant with increasing content of LiTaO3. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal phases appears at x=5-6 mol.%. Analogous to Pb(Zr,Ti)O3, the piezoelectric and electromechanical properties are enhanced for compositions near the morphotropic phase boundary. Piezoelectric constant d33 values reach ∼200 pC/N. Electromechanical coefficients of planar mode reach ∼36%, respectively. Our results show that (Na0.5K0.5)NbO3 with small amount of LiTaO3 (x=7 mol.%) is a good lead-free piezoelectric ceramic.