Dielectric, piezoelectric, and pyroelectric anisotropy in KCl-modified grain-oriented bismuth vanadate ceramics

The effect of the additive KCl, on the structural, microstructural, and polar properties of bismuth vanadate (BiV) ceramics is investigated. The scanning electron microscopic (SEM) studies reveal a remarkable modification in the microstructure and the occurrence of high grain-orientation (75%) on KCl addition. The energy dispersive x-ray (EDX) analyses indicate the presence of chemically inhomogeneous distribution of KCl, with core-shell-like grain structure. The KCl-modified BiV samples exhibit a broad and depressed phase transition, with no frequency dispersion, as a result of the increased internal stress and the formation of core-shell-like grain structure. Significant anisotropies are observed in the dielectric, piezoelectric, and pyroelectric responses of these grain-oriented ceramic samples. These samples are characterized by near rectangular ferroelectric hysteresis loops, with a significant anisotropy in the P_r (P_r┴/P_r∥ = 2.43, at 300 K) and E_c (E_c∥/E_c┴= 2.22, at 300 K) values between the directions parallel and perpendicular to the cold-pressing axis.