Effects of silver doping on ferroelectric SrBi ₂Ta ₂O ₉

Silver-doped SrBi ₂Ta ₂O ₉ (Ag:SBT) ceramics were synthesized by solid state reactions. The reaction mechanism has been deduced based on the crystal defect chemistry. It involves the diffusion of Ag ⁺ and O ^2- ions into the (Bi ₂O ₂) ²⁺ layers between the perovskite-like units to recover the bismuth and oxygen vacancies, respectively, which were inherently present in SBT ceramics due to the volatilization of Bi ₂O ₃ at high temperatures. The Ag:SBT samples have been characterized by a variety of techniques: x-ray diffraction, dielectric and ferroelectric measurements, and impedance spectroscopy. Ag doping is found to significantly affect the structural and physical properties of SBT, including lattice parameters, Curie temperature, bulk conductivity, activation energy, and ferroelectricity. These effects have been interpreted based on the model of the recovery of oxygen and bismuth vacancies upon Ag doping. The effects of Ag diffusion should be taken into account when using Ag as electrode materials for the characterization of the electric properties of SBT and related materials.