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.