Defect Structure and Electrical Property of Na_0.5K_0.5NbO₃ Lead-Free Piezoceramics

Na0.5K0.5NbO3 (NKN) lead-free piezoceramics was synthesized by a solid state reaction method. The d.c. conductivitydc and a.c. impedance of the ceramics were measured at the temperature range from 550 oC to room temperature on cooling process. Thedc decreased linearly with decreasing temperature on Arrhenius plot, and the activation energy at the temperature range from 450 to 390 oC and from 390 to 160 oC were 0.65 and 0.90 eV, respectively. The slope change at 390 oC corresponded to Curie temperature of NKN ceramics so that the carriers of these thermally active conductions were alkali metal or oxygen ions in the NKN crystal structure. The impedance of NKN ceramics at high temperature showed two relaxation processes at high and low frequencies, and the leak current was mainly attributed by the conduction through the grain boundary with low impedance value on lower frequency relaxation.