Electrical conductivity of mullite-type Bi2Al4O9 ceramics in air

For the electrical conductivity of Bi2Al4O9 based dense polycrystalline materials controversial data have been published in the literature. In this work samples with a nominal excess of Bi2O3 or SrO of up to 3 wt.% have been investigated in air using impedance spectroscopy. Both the results of this work and the literature data can be consistently interpreted on the basis of a simple model of the microstructure as consisting of Bi2Al4O9 grains and a well conducting grain boundary film (Bi2O3 based in the case of a Bi2O3 excess) or a poorly conducting grain boundary film (SrO based in the case of a SrO excess), respectively. It turns out that the degree of SrO doping in Bi2Al4O9 is much lower than suggested before. Thus an effect of SrO doping on the electrical conductivity of Bi2Al4O9 can be ruled out.