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 (Ag1-xKx)NbO3 ceramics was upgraded. In details, (Ag1-xKx)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, (Ag1-xKx)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.