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The electronic structure of the promising Li-ion battery anode material Li 7 MnN 4 synthesized by a solid-state reaction is studied using ab initio calculations completed by Raman spectroscopy experiments. The structural optimization reliably reproduces the experimental one, hence validating the accuracy of the chosen Density Functional Theory method. The theoretical analysis of the electronic structure reveals the nature of the valence band as composed from band filled by electrons with spin-up states only, which allows refuting literature data about the claimed electronic character of Li 7 MnN 4. Actually, the calculated electronic band gap E g = 0.95 eV is found to be in good agreement with available experimental data. A careful experimental approach provides the first experimental Raman spectra of hygroscopic Li 7 MnN 4 at 293 K and 130 K. The analysis of the phonon states in the Γ-point of the Brillouin zone, completed by the computation of the Raman scattering intensities of the vibrational modes of the Li 7 MnN 4 structure give a remarkable agreement between simulated and experimental Raman spectra. With such a good matching, a reliable assignment of all the observed Raman peaks to the vibrations of specific structural units in the Li 7 MnN 4 lattices is proposed. In particular, the most intense band in the Raman spectrum is ascribed to a totally symmetric MnN 4 breathing mode. We also show that, using different wavelengths of exciting radiation, the transition from off-resonance to resonance Raman scattering process can be observed. Furthermore, Raman spectroscopy is revealed as an efficient in situ diagnostic tool to control the degradation of the Li 7 MnN 4 powder in open air through the observation of extra bands in the Raman spectra. Results of this study shed a light on the understanding of the fundamental properties of Li 7 MnN 4 and pave a way for the upcoming operando Raman spectroscopy investigation of the atomic-scale induced structural changes of this negative electrode material for Li-ion battery. • Raman spectra of hygroscopic Li 7 MnN 4 (LMN) in 293 K and 130 K are reported for the first time. • DFT calculations well reproduce LMN experimental structure and Raman spectra. • Calculated electronic structure characterizes LMN as indirect band gap semiconductor with a narrow gap. • The calculations provide a complete explanation of the vibrational dynamics of the compound. • The oxidation state of Mn in LMN and the reactivity of LMN in air can be monitored by Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Highlights: [•] Minor role of the electron lone pairs of Te atom on non-linear optic properties. [•] TeIVO4 →TeVIO6 evolution induces an augmentation of the χ 3 susceptibility. [•] The Te-O-Te chain -length influences on the lattice χ 3 susceptibility. [ABSTRACT FROM AUTHOR]

Abstract: The dielectric properties of the glassy telluria have been modeled and studied via the ab initio calculations of the linear- and hyper-polarizabilities of chain-like (TeO2) n clusters. By using the localized molecular orbitals approximation (GAMESS program), it is shown that their linear polarizability is mainly associated with the tellurium atom lone pairs and with the Te–O–Te bridges, whose contributions are comparable. On contrary, the bridge contributions unequivocally dominate the hyperpolarizability value (providing 75% of this) whereas the role of the lone pair on tellurium atoms is minimal (5%). The same estimations can be obtained for the relevant characteristics of TeO2 glass. [Copyright &y& Elsevier]