Phase transitional behavior and piezoelectric properties of (Na0.5K0.5)NbO3–LiNbO3 ceramics

Lead-free piezoelectric ceramics (1−x) (Na0. 5K0. 5) NbO3–xLiNbO3 Lix (Na0. 5K0. 5) 1−xNbO3 (x=0. 04–0. 20) have been synthesized by an ordinary sintering technique. The materials with perovskite structure is orthorhombic phase at x⩽0. 05 and becomes tetragonal phase at x⩾0. 07, a phase K3Li2Nb5O15 with tetragonal tungsten bronze structure begins to appear at x=0. 08 and becomes dominant with increasing the content of LiNbO3. A morphotropic phase boundary between orthorhombic and tetragonal phases is found in the composition range 0. 05x0. 07. 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 200–235pC∕N. Electromechanical coefficients of the planar mode and the thickness mode reach 38%–44% and 44%–48%, respectively. The Curie temperatures (TC) of Lix (Na0. 5K0. 5) 1−xNbO3 (x=0. 04–0. 20) are in the range of 452–510°C, at least 100°C higher than that of conventional Pb (Zr, Ti) O3. Our results show that Lix (Na0. 5K0. 5) 1−xNbO3 is a good lead-free high-temperature piezoelectric ceramic.