Effects of A-site nonstoichiometry on oxide ion conduction in 0.94Bi0.5Na0.5TiO3–0.06BaTiO3 ceramics

Abstract

Lead free 0.94(Bi[Formula: see text]Na[Formula: see text]TiO3–0.06BaTiO3 ceramics were prepared by conventional solid-state mixed oxide route with the A-site stoichiometry modified to incorporate donor-doping (through Bi-excess) and acceptor-doping (through Na-excess). Both stoichiometric and nonstoichiometric ceramics exhibited a single perovskite phase with pseudo-cubic symmetry. A significant improvement in the dielectric properties was observed in Bi-excess compositions and a deterioration in the dielectric properties was observed in Na-excess compositions. Impedance spectroscopy was utilized to analyze the effects of A-site nonstoichiometry on conduction mechanisms. Compositions with Bi-excess resulted in an electrically homogeneous microstructure with an increase in resistivity by [Formula: see text]3–4 orders of magnitude and an associated activation energy of 1.57[Formula: see text]eV which was close to half of the optical bandgap. In contrast, an electrically heterogeneous microstructure was observed in both the stoichiometric and Na-excess compositions. In addition, the Na-excess compositions exhibited low resistivities ([Formula: see text]-cm) with characteristic peaks in the impedance data comparable to the recent observations of oxide ion conduction in (Bi[Formula: see text]Na[Formula: see text]TiO3. Long term annealing studies were also conducted at 800[Formula: see text]C to identify changes in crystal structure and electrical properties. The results of this study demonstrates that the dielectric and electrical properties of 0.94(Bi[Formula: see text]Na[Formula: see text]TiO3–0.06BaTiO3 ceramics are very sensitive to Bi/Na stoichiometry.