Microstructure, crystalline phase and electrical properties of Li_0.06(Na_0.5K_0.5)_0.94Nb_(1-2x/5)Mg_xO₃ lead-free piezoelectric ceramics

MgO-modified Li_0.06(Na_0.5K_0.5)_0.94NbO₃ (L₆NKN) lead-free piezoelectric ceramics were synthesized by normal sintering at a relatively low temperature of 1000℃. The crystalline phase, microstructure, and electrical properties of the ceramics were investigated with a special emphasis on the influence of MgO content. The addition of MgO effectively improves the sinterability of the L₆NKN ceramics. X-ray diffraction analysis indicates that the morphotropic phase boundary (MPB) separating orthorhombic and tetragonal phases for the ceramics lies in the range of Mg doping content (x) from 0.3at% to 0.7at%. High electrical properties of the piezoelectric constant (d₃₃=238 pC/N), planar electromechanical coupling coefficient (k_p=41.5%), relative dielectric constant (ε_r=905), and remanent polarization (P_r=38.3 μC/cm²) are obtained from the specimen with x=0.5at%, which suggests that the Li_0.06(Na_0.5K_0.5)_0.94Nb_(1-2x/5)Mg_xO₃ (x=0.5at%) ceramic is a promising lead-free piezoelectric material.