Structural, magnetic, optical, DFT, and temperature-dependent dielectric properties of Bi2Fe4O9 microcrystals

In the present work, we report mullite-type spin-frustrated multiferroic Bismuth Ferrite (Bi2Fe4O9) microcrystals synthesized using the solid-state reaction. The detailed structural, optical, magnetic, and temperature-dependent dielectric properties are reported. The XRD Rietveld refinement analysis confirms the formation of an Orthorhombic phase with space group of Pbam, lattice parameters a = 7.974(4) Å, b = 8.450(4) Å, and c = 6.008(4) Å. An optical bandgap of 1.98 eV is calculated by absorption spectroscopy. The SEM-EDS observations reveal the polycrystalline, cuboid-shaped micro particles of size 1.2 μm, and the EDS spectrum confirms the chemical stoichiometry composition. The photoluminescence shows the luminescence emission intensity of 750 nm when excited at 500 nm. The electrical properties in the temperature range of 30℃ to 300℃ confirm the existence of a non-Debye type of relaxation, and the dielectric constant is enhanced from 7.19 at 30⁰C to 69.89 at 300⁰C. The activation energy obtained from the DC conductivity suggests that oxygen vacancies play a major role in the conduction of Bi2Fe4O9 ceramic. Furthermore, the magnetic study confirms the soft magnetic nature of Bi2Fe4O9. From the VSM studies, magnetization and coercivity values are found to be 0.336 emu/g and 531.3 Oe, respectively. In addition, the periodic DFT studies were carried out to understand the band structure, density of states, and electronic properties of Bi2Fe4O9.