Vibrational and electron paramagnetic resonance spectroscopic studies of beta-MnO2 and alpha-KxMnO(2) nanorods

Abstract

Raman scattering (RS), Fourier transform infrared (FTIR) and electron paramagnetic resonance (EPR) spectroscopic measurements on beta-MnO2 and alpha-KxMnO2 nanorods were performed. The infrared spectrum of beta-MnO2 is sensitive towards the particle sizes, while the Raman spectrum is sensitive towards the presence of nonstoichiometric and disordered MnO2-delta 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-delta. Observed bands in vibrational spectra of tetragonal hollanditetype alpha-KxMnO(2) are considered to be mainly due to the vibration modes of Mn-O frameworks. The EPR spectra of alpha-KxMnO(2) 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. (C) 2017 Elsevier B.V. All rights reserved.