2 days of beamtime is requested on Polaris to study the defect structure of an oxide-ion conductor Bi1-xBaxFeO3-x/2. RT total neutron scattering studies on samples heat treated in air, contain Fe3+/Fe4+ and are dominated by electronic conduction and contrast with samples annealed in N2 where oxidation is suppressed and oxide-ion conductivity is appreciable. The oxide-ion conductivity does not show a strong dependence across a wide range of x and is not in agreement with the enhanced conductivity maximum associated with the cross over from weak- to strong-electrolyte behaviour commonly reported for acceptor-doped oxide-ion conductors. Total neutron scattering data are required to investigate possible changes in local structure via clustering of oxygen vacancies and/or ordering of metal ions. This could lead to new strategies to develop new electrolytes for fuel cells.