Structural, optical and magnetic tunability in KBiFe2O5 multiferroics

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 degrees 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.