Phase transition and piezoelectric property of (Ag, K)NbO₃ ceramics

AgNbO₃ is an antiferroelectric (AFE) material with double hysteresis loop. Both the antiferroelectricity and ferroelectricity can be enhanced by doping. Herein, the ferroelectricity of AgNbO₃ ceramics was enhanced via K-doping and the phase diagram of the (Ag_1-xK_x)NbO₃ ceramics was upgraded. In details, (Ag_1-xK_x)NbO₃ ceramics are ferrielectric (FIE) M₁ phase as x = 5.00–5.50 mol% and ferroelectric (FE) O phase as x = 5.75–6.00 mol% before poling, and FE O phase as x = 5.00–6.00 mol% after poling at room temperature. With increasing temperature, (Ag_1-xK_x)NbO₃ ceramics show the phase evolutions from FIE M₁, AFE M₂ to paraelectric (PE) T phase at x = 5.00–5.50 mol% and from FE O, FE T to PE T phase at x = 5.75–6.00 mol% before poling, and from FE O, FE T to PE T phase at x = 5.00–6.00 mol% after poling. High d₃₃ values of 180 pC/N and 285 pC/N are obtained at the FE O-FE T and FE T-PE T phase boundaries. This work sheds light on a novel and promising lead-free piezoelectric system.