The feasibility of doping Ga3+ into the Aurivillius family of layered perovskites was re-assessed in the light of the previously reported high oxide ion conductivity in these phases. Careful X-ray powder diffraction studies revealed that the Ga3+ solubility in both Bi2Sr2Nb2TiO12 and BaBi4Ti4O15 was very limited, and that the previously reported so-called O-deficient phases, Bi2Sr2Nb2GaO11.5 and BaBi4Ti3GaO14.5, were in fact mixtures; both containing a significant amount of a β-Bi2O3-related phase. Since this phase was known to transform to the highly conducting δ-Bi2O3 phase at high temperatures, reports of oxide ion conductivity in these O-deficient Aurivillius phases had to be treated with caution. This highlighted the importance of carefully characterizing complex materials in polycrystalline form, using a reliable structural model and quantitative profile-fitting, rather than simply indexing on the basis of peak position data alone.

Oxide Ion Conductivity in Ga-Doped Aurivillius Phases - a Reappraisal. A.Snedden, S.M.Blake, P.Lightfoot: Solid State Ionics, 2003, 156[3-4], 439-45