Wide Bandgap and Structural Homogeneity in Spray-Pyrolyzed CuNiFeO Spinel Ferrite Thin Films for Multifunctional Optoelectronics

Abstract

This study presents the synthesis of quaternary (Cu6Ni0.4Fe2O4 ) CuNiFeO thin films via spray pyrolysis, exhibiting high phase purity and structural uniformity. XRD confirmed a polycrystalline cubic spinel structure (Fd-3m) with a lattice parameter of 8.242 Å. Crystallite sizes (96.065–597.477 nm) and minimal lattice strain (0.250×10-3 to 2.294×10-3), derived from Debye-Scherrer and W-H analyses, respectively, indicate highlight low crystallographic defects. SEM revealed dense, homogeneous nanoscale grains (11.45-17.48 nm), consistent with aligning with the fine-grained microstructure. FTIR identified metal-oxygen bonds (464 cm-1), confirming Ni-O, Cu-O, and Fe-O vibrations in the spinel framework. UV-Vis-NIR spectra showed absorption peaks at 217 nm (Cu2+ charge transfer), 344 nm (Ni3+ transitions), and additional peaks corresponding to Fe3+ d-d excitations. A direct bandgap of 5.26 eV (via Tauc’s plot) underpins strong UV-C/UV-B absorption (>90% below 300 nm) and high visible transparency (>80% at 500-800 nm). These optical traits, coupled with structural coherence, position the films for UV-filtering and transparent conductive technologies, leveraging their dual functionality.