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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]

Highlights: [•] The detailed P–T phase diagram of BiMnO3 was established. [•] We found three monoclinic modifications of BiMnO3 at pressure and temperature. [•] A suppression of monoclinic C2/c phase have been observed under pressure. [•] We found a new orthorhombic Imma phase of BiMnO3 at P >20GPa. [Copyright &y& Elsevier]

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]

Edingtonite is a ferroelectric material of the Rochelle salt (RS) class and shows large anomalies of different properties in the temperature range of −53 to −133 °C. Classical RS exhibits the low-temperature phase transition P21212–P2111, whereas ammonium RS shows the phase transition P21212–P11211. According to our data, edingtonite blocks this possible symmetry lowering by the phase transition P21212–P112. Edingtonite, similarly to RS crystals, has two sub-lattices of water molecules and exhibits a complex low-temperature behavior. There are at least three anomalies in the low-temperature dependence of the generation of the second optical 0.53-micron harmonics, excited by the 1.06-micron line of a Nd pulse laser.Edingtonite also exhibits significant anomalies in the low-frequency range of its IR spectrum at low temperatures. The maximum IR anomaly is observed in natural edingtonite at −124 °C, whereas in the deuterated sample the same anomaly occurs at −113 °C. The most intense anomalous broad band at 220 cm−1 did not shift due to deuteration. According to the presented lattice-dynamical calculations, this vibration corresponds to a strong deformation of the cavity around the water molecules during the phase transition.Raman study of edingtonite under high pressure in a diamond anvil cell (DAC) at room temperature shows that there is no pressure-induced phase transition up to 6.4 GPa. No amorphization was observed at this pressure range. [Copyright &y& Elsevier]