Effects of Silver on Barium Titanate as a Function of Stoichiometry

This work examines the effects of Ag on stoichiometric and nonstoichiometric BaTiO₃ in terms of the unit cell dimensions, the polycrystalline microstructure, and the dielectric properties. Stoichiometric BaTiO₃ and compositions with 0.5 mol% TiO₂ excess and 0.5 mol% BaO excess were prepared via solid-state synthesis with varying amounts of Ag up to 0.3 mol%. Experimental results indicate that stoichiometry plays a significant role in the solubility of Ag and its effects on the physical properties. Overall, the solubility of Ag was negligible in stoichiometric BaTiO₃. However, compositions with excess TiO₂ stabilized the solubility of Ag as evidenced from changes in the unit cell dimensions and dielectric properties. Based on these data, it is proposed that Ag occupies the A-site in the perovskite structure with an upper limit of Ag solubility of 0.06 mol% Ag in BaTiO₃ with 0.5 mol% excess TiO₂. Dielectric measurements showed that Ag concentrations approaching 0.3 mol% gave rise to an increase in the space charge effect, especially at temperatures above T _C. In both nonstoichiometric compositions, the presence of a liquid Ag phase during thermal processing was found to affect microstructural development and sintering.