(50% Ti at B-site) composition, resembling characteristics of a lossy dielectric. For the Fecontaining Bi4Bim-3Fem-3Ti3O3m+3 phases, it was previously shown that the leakage current increased as m increased from 4 to 6. The presence of non-ferroelectric secondary-phase impurities within the Bi6Ti2.50Fe1.77Mn0.73O18 sample, constituting a volume fraction of 2.7 vol.% (See Supplementary Information section SI4.3), could also be a factor influencing domain wall pinning, the reduced polarization value, the increased coercive field and an altered hysteresis loop shape. Furthermore, the presence of trace levels of secondary phase impurities would complicate attempts to measure a magnetic signal intrinsic to the main Aurivillius phase, therefore magnetic measurements of the new compositions could not be reliably performed in this work.