Computer modelling techniques have been used to investigate the defect and oxygen transport properties of the Aurivillius phase Bi4Ti3O12. A range of cation dopant substitutions has been considered including the incorporation of trivalent ions (M3+ = Al, Ga and In). The substitution of In3+ onto the Bi site in the [Bi2O2] layer is predicted to be the most favourable. The calculations suggest that lanthanide (Ln(3+)) doping at the dilute limit preferentially occurs in the [Bi2O2] layer, with probable distribution over both the [Bi2O2] and the perovskite A-site at higher dopant levels. It is predicted that the reduction process involving Ti3+ and oxygen vacancy formation is energetically favourable. The energetics of oxide vacancy migration between various oxygen sites in the structure have been investigated. (C) 2004 Elsevier Inc. All rights reserved.