Effects of Ni substitution on multiferroic properties in Bi₅FeTi₃O₁₅ ceramics

The single-phase multiferroic Bi₅Fe_1-xNi_xTi₃O₁₅ (BFNT-x, x=0, 0.1, 0.2, 0.3, 0.4, and 0.5) ceramics were synthesized by a sol-gel auto-combustion method, and their microstructures, ferroelectric, magnetic, and dielectric properties were investigated in detail. All samples belong to layer-perovskited Aurivillius phase containing four perovskite units sandwiched between two Bi-O layers. Ni substitution can not only improve ferroelectricity but also enhance the magnetic properties. The BFNT-0.2 sample shows the largest remnant polarization (2P_r ～ 11.6 μC/cm²) and the highest remnant magnetization (2M_r ～ 0.244 emu/g). The enhancement of the magnetic properties may mainly originate from the spin canting of Fe/Ni-O octahedra via Dzyaloshinskii-Moriya (DM) interaction. In order to explore the influence of valance state of magnetic ions on the properties, the x-ray photoelectron spectroscopy was carried out. Furthermore, structural, ferroelectric, and magnetic transitions were also investigated.