Electrical conductivity of mullite-type Bi2Al4O9 ceramics in air

► Electrical conductivity of Bi2Al4O9 ceramics in air was investigated. ► Samples with a nominal excess of Bi2O3 or SrO of up to 3 wt.% were used. ► The degree of SrO doping in Bi2Al4O9 is much lower than suggested before. ► Conductivity is dominated by well conducting Bi2O3-based grain boundary films.