Determination of the optical band gap and electronic transition type of powdered Ca2Fe2O5 brownmillerite

In this study, powdered Ca 2 Fe 2 O 5 was synthesized via a sol-gel method and characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and ultraviolet–visible–near infrared diffuse reflectance spectroscopy (UV–Vis–NIR DRS). The morphology of the particles was analyzed with SEM, the elemental composition was studied with EDX and XRD; the latter, along with ATR-FTIR, confirmed both the crystal phase and sample purity. The novelty of this study lies in the application of two recently developed methods for analyzing UV–Vis/NIR data, which allow the determination of the Tauc exponent when calculating the optical band gap from Tauc plots. Both methods indicated an indirect electronic transition in Ca 2 Fe 2 O 5 , with the resulting optical band gap value being 1.62 eV. This indirect transition aligns with the results from theoretical works on the electronic band structure of the material. However, the obtained band gap is substantially lower than those reported in previous theoretical and experimental reports. • Ca 2 Fe 2 O 5 brownmillerite was synthesized via a sol-gel method. • XRD and FTIR confirmed a brownmillerite crystal structure described by Pnma symmetry. • The band gap estimated with DASF matched very well with the obtained using LOGF . • Both LOGF and DASF methods yielded γ values indicative of an indirect transition. • Therefore, we report an E g opt of 1.62 eV for the Ca 2 Fe 2 O 5 sample prepared herein.