However, the Aurivillius phase structure is expected to have a limit on the concentration of Fe and Mn it can accommodate. One constraint stems from differences in cation radii: when coordinated octahedrally by oxygen, Ti⁴⁺ has a radius of 0.605 Å, whereas both Fe³⁺ and Mn³⁺ (in their high-spin states) have a radii of 0.645 Å. (NB: The high-spin state is favored for transition metals in Aurivillius phase structures due to structural and electronic factors. These include the large size of bismuth resulting in weakened ligand fields, distortion in the coordination environment due to neighboring layers, and incomplete hybridization between metal d orbitals and ligand orbitals. ) Another limitation arises because these cations have a nominal valence of 3+, and they replace Ti⁴⁺, which has a valence of 4+. Substituting Ti 4+ by Mn 3+ /Fe 3+ requires charge compensation, for which several mechanisms can be postulated. One possibility for charge compensation is through changes in the oxidation states (o.s.) of the Mn or Fe cations. Alternatively, exceeding the solubility limit may lead to the segregation of impurity species or the formation of secondary phases at grain boundaries or surfaces. Another potential mechanism is ionic compensation through the introduction of ionic defects such as oxygen vacancies. However, in Aurivillius phase materials, the [Bi2O2] 2+ layers are recognized for their important role in space charge compensation and prevention of oxygen vacancies, which in turn reduces leakage currents and enhances fatigue resistance. Given these considerations, it is important to understand how increasing the concentration of magnetic ions in m = 5 Aurivillius phases affects the crystal structure. To investigate this, we systematically varied the concentrations of the three B-site atoms (Ti, Fe and Mn) in the B6TFMO system, Bi6TixFeyMnzO18 (x = 2.3 to 3.2, y = 1.2 to 2.0, z = 0.3 to 0.9). This approach enabled us to determine the solubility limit of magnetic ion inclusion in the m = 5 Aurivillius phase structure and assess its impact on the superlattice layering. We consider the above size and charge compensation mechanisms and demonstrate that structural reorganization into higher m phases is a further option available to the versatile Aurivillius phase structures to accommodate a greater magnetic ion fraction while preserving in-plane ferroelectric properties. Furthermore, we show that aliovalent substitution using transition metal cations, through simple chemical solution deposition processes, can overcome thermodynamic challenges of synthesizing higher-layered Aurivillius homologues without requiring epitaxial substrates or kinetically limited growth processes.