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.
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