Effect of Ag substitution on ferroelectricity in KNbSi₂O₇

Abstract

The ferroelectric properties of Ag_xK_1−xNbSi₂O₇ (x = 0–0.10) single crystals were evaluated to understand the effect of Ag substitution on ferroelectricity in KNbSi₂O₇. Millimeter-sized plate-like Ag_xK_1−xNbSi₂O₇ single crystals were fabricated by crystallization of the glass phase. The remanent polarization of Ag_xK_1−xNbSi₂O₇ decreased with increasing the amount of Ag, meaning that the ferroelectricity of KNbSi₂O₇ is reduced by Ag substitution. Such a tendency was also confirmed by first-principles calculations for KNbSi₂O₇ and AgNbSi₂O₇. The displacement of Nb from the center of gravity of the NbO₆ octahedron and the rotation of the NbO₆ octahedron around the c-axis were smaller in AgNbSi₂O₇ than in KNbSi₂O₇. These may be due to the larger electronegativity and smaller ionic radius of Ag. The similarities between the Ag_xK_1−xNbSi₂O₇ and Ag_xK_1−xNbO₃ were also discussed.