Phase transition and electrical properties of (1-x)(K_1/2Na_1/2)NbO_3-xBi(Sc_3/4Co_1/4)O₃ lead-free ceramics

Lead-free ceramics (1 - x)(K_1/2Na_1/2)NbO_3-xBi(Sc_3/4Co_1/4)O₃ [(1 - x)KNN-xBSC] were prepared by the conventional solid-state sintering method. X-ray diffraction patterns show that the introduction of BSC into KNN system caused insignificant change in crystal structure. The composition with x = 0.015 has diphasic tetragonal and orthorhombic phases. Moreover, the grain size significantly dependent on the composition. The phase transition temperatures of orthorhombic-tetragonal (T_O-T) and tetragonal-cubic (T_C) decreased with increasing x from 0 to 0.025. The T_O-T value of KNN-0.015BSC ceramic is close to room temperature, resulting in good electrical properties (d₃₃ = 190 pC/N, k_p = 40.3%, ε_r = 1494, tgδ = 0.026), with the Curie temperature T_C = 321 °C. The combination of good piezoelectric properties and high T_C makes these KNN-BSC ceramics suitable for elevated temperature piezoelectric devices.