Electrical conductivity of SrBi2Ta2O9 ceramics

Aurivillius SrBi2Ta2O9 (SBT) ceramics were prepared by applying the conventional solid state reaction method. The grain structure and stoichiometry were investigated with the use of a scanning electron microscope with an energy dispersion X-ray spectrometer (EDS). The X-ray diffraction studies revealed an orthorhombic structure with lattice parameters a=5.486 Å, b=5.497 Å and c=24.91 Å in the SBT. Dielectric properties were determined by impedance spectroscopy measurements. It was found that a strong low-frequency dielectric dispersion was present in this material. Its occurrence was ascribed to the presence of ionized space charge carriers such as oxygen vacancies. Dielectric relaxation was defined on the basis of an equivalent circuit. The temperature dependence of various electrical properties is described and discussed. The thermal activation energy for the grain electric conductivity was lower in the high temperature region (T>328.5 °C, Ea−ht=0.23 eV) and higher in the low-temperature region (T<328.5 °C, Ea−lt=0.78 eV). Moreover local conductivity measurements were performed with the use of the local conductive atomic force microscope method.