Influence of Mg2+ doping on the oxide ion conductivity of layered ferroelectric SrBi2Ta2O9

Layered perovskites structures are an interesting candidate to explore as a potential electrolyte materials for Solid oxide fuel cell (SOFC) applications. However, achieving a high ionic conductivity (-0.01 S cm-1 below 650 degrees C) remains a significant challenge to lowering the SOFC operating temperatures. SrBi2Ta2O9 (SBT), an Aurivillius-based layered perovskite, is a well-known ferroelectric material with TC of 320 degrees C. Site exchange and Bi volatility related defects lead to ionic conductivity in SBT above 700 degrees C. Here, we aim to control the defect chemistry by doping to promote the oxygen vacancies. We show that Mg doping at the Ta-site in the perovskite block results in 4-fold increase in the bulk conductivity of SBT 3.65 x 10-4 S cm-1 and improvement in the ionic transport number from 0.26 to 0.71. The study provides an opportunity to design new oxide ion conductors in layered ferroelectric oxides.