Identification of Cobalt Oxides with Raman Scattering and Fourier Transform Infrared Spectroscopy

Although Raman spectral fingerprints of Co3O4 have been well established, the infrared spectrum of Co3O4 is less understood due to its dependence on sample morphologies and experimental configurations. The same is true for both Raman and infrared spectra of CoO. In this study, we present a comprehensive optical characterization of Co3O4 and CoO with Raman scattering and Fourier transform infrared spectroscopy (FTIR). Two of the transverse optical (TO) phonons and their corresponding longitudinal optical (LO) phonons of Co3O4 above 500 cm–1 are observed in both transmission and diffuse reflectance with LO/TO intensity ratios depending on particle size and the incident angle of FTIR beam. CoO is featured by a broad infrared band around 510 cm–1. In contrast to many previous reports, no Raman-active phonon line is observed, which is in agreement with the selection rule for rock-salt CoO. Nevertheless, CoO can still be characterized by Raman scattering from magnetic excitations in its antiferromagnetic phase at low temperature and a two-phonon Raman band at ∼1060 cm–1.