Effects of sintering temperature and alkaline elements excess on the structure and electrical properties of (K_0.462Na _0.48Li_0.058)_1+xNbO₃ lead-free piezoelectric ceramics

Lead-free (K_0.462Na_0.48Li_0.058) _1+xNbO₃(0 ≤ x ≤ 0.03) ceramics with excessive alkaline elements were synthesized by conventional ceramics processes as functions of sintering temperatures and quantities of excess alkaline elements. X-ray diffraction results reveal a transformation from tetragonal phase to orthorhombic phase with increasing the contents of excessive alkaline elements. The grain size and the piezoelectric properties were enhanced when a certain amount of excessive alkaline elements were added. Further elevation in the amount of alkaline elements added resulted in excessive liquid phase in the ceramics and deteriorated the piezoelectric properties. With x = 0.01, the ceramics sintered at 1050 °C show better properties of planar electromechanical coupling factor k_p = 43.4%, piezoelectric constant d₃₃ = 204 pC/N, dielectric constant ε33T/^ε0=704. 4, and loss tangent tan δ = 2.8%.