Raman single crystal studies of spinel type MCr2S4(M  Mn, Fe, Co, Zn, Cd), MIn2S4(M  Mn, Fe, Co, Ni), MnCr2–2xIn2xS4 and Co1‐xCdxCr2S4

Lutz, H. D.; Becker, Wilfried; Müller, Beate; Jung, M.

doi:10.1002/jrs.1250200207

Cited by 56 publications

(26 citation statements)

References 22 publications

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“…At ~11 GPa we noticed an abrupt frequency downshift of the most intense E g mode, which corresponds to a Se bending motion 59 , as well as an overall Raman intensity reduction in our spectra (Fig. 2).…”

Section: Resultsmentioning

confidence: 52%

Pressure-induced phase transitions in the CdCr2Se4 spinel

et al. 2016

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We have conducted high-pressure x-ray diffraction and Raman spectroscopic studies on the CdCr 2 Se 4 spinel at room temperature up to 42 GPa. We have resolved three structural transitions up to 42 GPa, i.e. the starting Fd3 m phase transforms at ~11 GPa into a tetragonal I4 1 /amd structure, an orthorhombic distortion was observed at ~15 GPa, whereas structural disorder initiates beyond 25 GPa. Our ab initio DFT studies successfully reproduced the observed crystalline-to-crystalline structural transitions. In addition, our calculations propose an anti-ferromagnetic ordering as a potential magnetic ground state for the high-pressure tetragonal and orthorhombic modifications, as compared to the starting ferromagnetic phase. Furthermore, the computational results indicate that all phases remain insulating in their stability pressure range, with a direct-to-indirect band gap transition for the Fd3 m phase taking place at 5 GPa.We attempted also to offer an explanation behind the peculiar first-order character of the Fd3 m (cubic)→I4 1 /amd (tetragonal) transition observed for several relevant Cr-spinels, i.e. the sizeable volume change at the transition point, which is not expected from space group symmetry considerations. We detected a clear correlation between the cubic-tetragonal transition pressures and the next-nearest-neighbor magnetic exchange interactions for the Crbearing sulphide and selenide members, a strong indication that the cubic-tetragonal transitions in these systems are principally governed by magnetic effects.

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Section: Resultsmentioning

confidence: 52%

Pressure-induced phase transitions in the CdCr2Se4 spinel

et al. 2016

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“…Wavenumber (era-t) When Li + ions are inserted into the LiMn204 spinel framework, it transforms to the LizMn204 rock-salt phase that has a tetragonal structure with I4Jamd ( 19 D4h) space group [23]. In this structure Mn 3+ ions occupy the 8d contributing to the infrared spectra of spinel phases vary from compound to compound, depending on the masses, charges, and chemical properties of ions [26]. The vibrational stretching frequency of the LiO4 tetrahedron has appeared out at 472 cm -~ in Li3PO 4 [24], whereas the frequency 435 cm -~ is pointed in the spinel LiFeCr4Os [25].…”

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confidence: 99%

Local structure of manganese oxides and lithium intercalates

Julien

Massot

2005

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The aim of this work is to determine the vibrational properties of manganese oxide frameworks and their lithium intercalates used as positive electrode material in Li-ion batteries. Raman and FTIR spectroscopies yield reliable description of material structure in which distortion of the basal MnO6 octahedra may be expected. Lattice dynamics are studied using either a classical group theoretical analysis or a local environment model. The local arrangement in MnO2 structures is investigated for pyrolusite, ramsdellite and the Li0.33MnO2 phase. The phase evolution as a function of the degree of lithium intercalation or deintercalation is reported and analysed in series of manganospinels Li1–x+δMn2–δO4 with 0≤x≤1 and 0≤δ≤0.33. The trigonal distortion of MnO6 octahedra is evidenced by insertion of lithium ions into the [B2]O4 spinel framework. A comparison with tetragonal Li2Mn2O4 and Li6.5Mn5O12 spinels shows the influence of the Jahn-Teller effect on the Raman features for this class of materials. The local structure was characterized as a function of the mean oxidation state of manganese cations

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“…The value of X is close to 0 (w0.057) which implies a slight deviation from the absolute inverse spinel structure. A low concentration of Fe in tetrahedral position, which is suggested by the appearance of the second A 1g mode (344 cm À1 ) in the Raman spectra of FeIn 2 S 4 crystals, was also previously observed by Lutz et al [35].…”

Section: Resultsmentioning

confidence: 53%