Deciphering the Origin of the Oxygen Defects in Single Phase CoNb₂O₆ Nanofibers Probed by Raman Scattering

In this study, we investigate the oxygen defects in cobalt niobate (CoNb₂O₆) by using Raman scattering and FTIR spectroscopy. Columbite niobate compounds, such as CoNb₂O₆, are known for their unique dielectric, magnetic, and photocatalytic properties, making them suitable for various applications, including microwave resonators and filters, Li-ion batteries, and white LED technologies. The CoNb₂O₆ structure comprises NbO₆ and CoO₆ octahedra with oxygen atoms classified into terminal, bridge, and chain positions based on their bonding environment. Our measurements reveal the activation of symmetry-forbidden oxygen-related phonon modes, specifically a Raman-forbidden mode (B_2u symmetry) at 782 cm^-1 in Raman spectra and an IR-forbidden mode (A_g symmetry) at ∼875 cm^-1 in FTIR spectra, indicating the presence of oxygen-related defects. Furthermore, Raman mapping shows a random distribution of intensities for the defect mode, particularly near sample cracks, suggesting an association with oxygen vacancies. These findings enhance our understanding of the impact of defects on the spectral features of CoNb₂O₆ and provide insight into the distribution of defects in this material.