Vibrational and electron paramagnetic resonance spectroscopic studies of β-MnO2 and α-KxMnO2 nanorods

Raman scattering (RS), Fourier transform infrared (FTIR) and electron paramagnetic resonance (EPR) spectroscopic measurements on β-MnO2 and α-KxMnO2 nanorods were performed. The infrared spectrum of β-MnO2 is sensitive towards the particle sizes, while the Raman spectrum is sensitive towards the presence of nonstoichiometric and disordered MnO2-δ on the surface of nanorods. EPR measurements show the appearance of two types of Mn4+ ions having different local environment: (i) Mn4+ ions in Mn4+-rich environment and (ii) Mn4+ ions in mixed-valence Mn4+/Mn3+ environment that match up with region of nonstoichiometric MnO2-δ. Observed bands in vibrational spectra of tetragonal hollandite-type α-KxMnO2 are considered to be mainly due to the vibration modes of MnO frameworks. The EPR spectra of α-KxMnO2 nanorods contain two signals that can be attributed to Mn4+ ions in Mn4+-rich environment and Mn4+ ions in mixed-valence Mn4+/Mn3+ environment close to K+ ions.