High oxide-ion conductivity in acceptor-doped Bi-based perovskites at modest doping levels

A combination of impedance spectroscopy, time-of-flight secondary ion mass spectrometry and literature data are used to show that, (i) the bulk oxide ion conductivity of A-site, alkaline earth-doped BiFeO 3 (BF) is independent of the ionic radius of the alkaline earth ion (Ca, Sr, Ba) and, (ii) despite very different A-site environments in (Na 1/2 Bi 1/2 )TiO 3 and BF, similar high levels and optimisation of bulk oxide ion conductivity in these Bi-based tilted perovskites is achieved at modest acceptor doping levels of ∼1-10%. These results clearly demonstrate that optimisation of oxide ion conductivity in these materials requires concepts beyond a simple crystallochemical approach based on matching the ionic radii of acceptor dopant and host lattice ions. High oxide ion conductivity is achieved in A-site alkaline earth doped BiFeO 3 at modest levels. The similar levels of conductivity suggest oxide-ion conduction in Bi-based tilted perovskites is beyond a simple radius-based crystallochemical approach.