Probing Oxide Ion Conductivity in Na0.5Bi0.5TiO3–BiFeO3–BaTiO3-Based Ferroelectric Materials

Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free perovskite that exhibits ferroelectricity below 300 °C. NBT and certain other ferroelectrics, e.g., Bi4Ti3O12, show oxide ionic conductivity on the order of 10–2 S cm–1 at elevated temperatures of 650 °C. The origin of ionic conductivity in these ferroelectric oxides has been explained in terms of bismuth deficiency and oxygen vacancy in the perovskite. There is a quest for materials as electrolytes with higher ionic conductivity and at temperatures below 650 °C. NBT-based ferroelectrics have been proposed to be one such candidate for low-temperature ionic conductors as electrolytes in solid oxide fuel cells (SOFCs). In this work, we have explored Na0.5Bi0.5TiO3–BaTiO3–BiFeO3 and studied the effect of composition on the conductivity behavior using impedance and modulus spectroscopy. We explain the nature of conductivity using the dependence of impedance on the partial pressure of oxygen. At a low BaTiO3 content, the composition Na0.45Bi0.49Ba0.05Fe0.05Mg0.019Ti0.931O3-δ (NBBTF-C) forms with a rhombohedral structure and shows an ionic conductivity of ∼1.02 × 10–3 S cm–1 at 600 °C, which is similar to that of NBT.