An analysis of derivative absorption spectroscopy of multiferroic bismuth ferrite in bulk, nanostructured, and film forms to inspect its Urbach energy and electronic structure
摘要
The study analyzed the probability density function (PDF) and cumulative density function (CDF) of bulk BiFeO3, nanostructured BiFeO3, and a thick film of BiFeO2.85 using their experimental absorption data. It identified charge transfer transitions in the energy range of 2.5 eV–5.5 eV, as well as two doubly degenerate d-d transitions of Fe3+ ions in the FeO6 octahedra within the range of 1.5 eV–2.5 eV for these BiFeO3-based materials. Additionally, the BiFeO3-based materials displayed strong direct and weak indirect transitions near the band edge, confirming a complex band structure of BiFeO3. Particularly, it was determined that the direct band gap energy (Eg) is about 2.46 eV, 2.47 eV, and 2.32 eV for bulk BiFeO3, nanostructured BiFeO3, and the BiFeO2.85 thick film, respectively. Lastly, the energy of the defect-induced Urbach tail band was calculated by analyzing the CDF function of the materials, resulting in the Urbach energy (EU) values of approximately 0.40 eV, 0.31 eV, and 0.33 eV for the bulk, nanostructured, and film samples, respectively. These findings are in line with the results obtained using conventional methods like the Tauc plot and Urbach analysis.