Tunable nanoscale structural disorder in Aurivillius phase, n = 3 Bi4Ti3O12 thin films and their role in the transformation to n = 4, Bi5Ti3FeO15 phase

Naturally super-latticed Aurivillius phase ferroelectrics can accommodate various magnetic ions, opening up the possibility of making new room temperature multiferroics. Here, we studied the growth of single-phase Aurivillius phase Bi5Ti3FeO15 (BTFO) thin films, grown onto single crystalline SrTiO3 (STO) substrates, by doping Bi4Ti3O12 (BTO) with iron by liquid injection metal-organic chemical vapour deposition. The crystalline properties of the resulting films were characterized by X-ray diffraction and transmission electron microscopy. It has been found that the structural properties of the films depend strongly on the relative iron and titanium precursor injection volumes. Nanoscale structural disorder starts to occur in BTO films on the onset of iron precursor flow. A small iron precursor flow causes the formation of half-unit cells of BTFO inside BTO lattice, which in turns causes disorder in BTO films. This disorder can be tuned by varying iron content in the film. Atomic force microscopy shows how the growth mode switches from island growth to layer-by-layer growth mode as the composition changes from BTO to BTFO