Dielectric, ferroelectric, and piezoelectric behaviors of AgNbO3–KNbO3 solid solution

Phase evolution in the (Ag1−xKx)NbO3 (AKN) solid solution was investigated by x-ray diffraction, dielectric, and ferroelectric measurements. At room temperature, there are three phase boundaries at xc1≈0.07, xc2≈0.20, and xc3≈0.8. When xc1<x, AKN transforms from the AgNbO3-type orthorhombic phase with a weak ferroelectricity into a new orthorhombic phase with a strong ferroelectricity. This ferroelectric phase is stable for xc1<x<xc2, and shows a nearly composition-independent Curie point of 525 K and a very large polarization (Pr=20.5 μC/cm2 for a ceramics sample of x=0.1). When xc2<x<xc3, single-phase AKN was not available. When xc3<x, AKN adopts the KNbO3-type orthorhombic structure and shows similar successive phase transitions to pure KNbO3. Its Curie point increases linearly with x from 633 K for x=0.80 to 696 K for x=1.00. We obtained a strain level of ≈0.05% and a d33 value of 46–64 pC/N for the AKN ceramics samples. The relationship between the structural change and ferroelectric phase evolution is also discussed briefly.