Structural, optical and magnetic tunability in KBiFe2O5 multiferroics

Abstract

KBiFe₂O₅, a highly promising multiferroic for perovskite solar cells, has been fabricated using a one-step thermal treatment method. The resulting products were characterized by X-ray diffraction, scanning electron microscopy and ultraviolet-visible-near-infrared spectroscopy. The effect of temperature on the formation of KBiFe₂O₅ polycrystallites was assessed, and we found that the reaction temperature is the key factor in determining the optical properties of the final products. Pure multiferroic KBiFe₂O₅ forms at a temperature of 850 °C with a narrow band gap of 1.65 eV, which is due to the stronger covalent character of Fe–O in FeO₄ than that in FeO₆ accompanying the inverted t_2g/e_g orbitals of tetrahedra. The magnetic transition from paramagnetism to ferromagnetism corresponds to the site of Fe³⁺, and the magnetic moment modification in the ferromagnetic phase in KBiFe₂O₅ could be correlated with the temperature and distortion of the unit cell. These results are helpful in the deeper understanding of the relationship between the crystal structure and the physical properties in perovskite-like oxides and show the potential role such materials can play in perovskite solar cells and multiferroic applications.