Raman scattering study of α-MgH2 and γ-MgH2

Kuzovnikov, Mikhail A.; Efimchenko, Vadim S.; Filatov, E. V.; Максимов, А. А.; Tartakovskii, I. I.; Ramirez‐Cuesta, Anibal J.

doi:10.1016/j.ssc.2012.09.022

Cited by 13 publications

(8 citation statements)

References 13 publications

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“…Orthorhombic γ-MgH 2 belonging to the space group Pbcn has four Raman-active modes: 1A g , 3B 3g , 2A g , and 3B 1g at 186, 509, 660, and 706 cm −1 , respectively, being the most intense the third of them. 23,29 This finding confirms the high pressures involved in the process. Figure 3C shows a representative spectrum (iii) of Mg(OH) 2 found in the transition zone (III).…”

supporting

confidence: 63%

Tribochemical Decomposition of Light Ionic Hydrides at Room Temperature

Nevshupa

Ares

Fernández

et al. 2015

J. Phys. Chem. Lett.

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Tribochemical decomposition of magnesium hydride (MgH2) induced by deformation at room temperature was studied on a micrometric scale, in situ and in real time. During deformation, a near-full depletion of hydrogen in the micrometric affected zone is observed through an instantaneous (t < 1 s) and huge release of hydrogen (3-50 nmol/s). H release is related to a nonthermal decomposition process. After deformation, the remaining hydride is thermally decomposed at room temperature, exhibiting a much slower rate than during deformation. Confocal-microRaman spectroscopy of the mechanically affected zone was used to characterize the decomposition products. Decomposition was enhanced through the formation of the distorted structure of MgH2 with reduced crystal size by mechanical deformation.

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supporting

confidence: 63%

Tribochemical Decomposition of Light Ionic Hydrides at Room Temperature

Nevshupa

Ares

Fernández

et al. 2015

J. Phys. Chem. Lett.

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“…The alkaline-earth hydrides such as beryllium hydride (BeH 2 ), magnesium hydride (MgH 2 ), calcium hydride (CaH 2 ), strontium hydride (SrH 2 ), and barium hydride (BaH 2 ) are the interesting class of compounds for hydrogen storage applications. , It is experimentally well-known that MgH 2 is less stable compared with other ionic hydrides such as CaH 2 , SrH 2 , and BaH 2 . Among all the alkaline-earth hydrides, MgH 2 has been much studied both experimentally − and theoretically − for energy storage applications due to its low manufacturing cost and high gravimetric hydrogen density (7.6 wt %), as well as high volumetric hydrogen density (110 kg/m 3 ). But, the dehydrogenation of MgH 2 requires higher temperature, that is, 552 K (300 °C) at 1 atm. − The high enthalpy of formation (Δ H = −75 kJ/mol) and very slow hydrogenation/dehydrogenation kinetics led MgH 2 as a challenging energy storage material.…”

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confidence: 99%

Phase Stability, Phase Mixing, and Phase Separation in Fluorinated Alkaline Earth Hydrides

Varunaa¹,

Ravindran

2017

J. Phys. Chem. C

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Alkaline-earth hydrides (AH2) are considered as potential hydrogen storage material. Due to high decomposition temperature and slow sorption kinetics, these hydrides cannot be used for energy storage applications. As fluorine is more electronegative than hydrogen, substitution of hydrogen by fluorine will bring anisotropic bonding interaction, and hence, it may improve the hydrogen storage properties. Hence, the structural stability, electronic structure, and chemical bonding of AH2 and fluorinated AH2 (AH2–x F x ) are delineated using ab initio calculations. From the calculated enthalpy of formation we have predicted that AH2–x F x are relatively more stable than the corresponding pure hydrides. The positive and very low value of enthalpy of mixing for AH2–x F x imply that single-phase of AH2–x F x may form at reasonable temperatures. The band structure and density of states (DOS) calculations reveal that AH2–x F x are insulators. Partial DOS, charge density, electron localization function, and crystal orbital Hamiltonian population analyses conclude that these compounds are governed mainly by ionic bonding. The calculated H site energy increases as the fluorination increases and thus fluorination bring extra stability in the lattice. The present results suggest that hydrogen closer to fluorine can be removed more easily than that far away from fluorine. Hence, the fluorination brings disproportionation in the bonding between the constituents.

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“…Raman-active ones are B 1g , E g , A 1g , and B 2g . The lattice vibration of MgH 2 at room temperature (RT) has been studied in experiment by means of inelastic neutron and Raman scattering. − In Raman spectra, peaks in the vicinity of 310, 940, and 1270 cm –1 are assigned to the B 1g , E g , and A 1g modes, respectively. The temperature dependence of lattice vibration in MgH 2 is, however, rarely reported.…”

Section: Introductionmentioning

confidence: 99%

Temperature-Dependent Lattice Vibration of Magnesium Hydride

Cai

Zhou

et al. 2018

J. Phys. Chem. C

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The thermodynamic stability of magnesium hydride hinders its application as a hydrogen storage medium. Efforts to destabilize MgH2 demonstrate the undesired reduction of entropy concomitant with the decrement of enthalpy. Lattice vibration contributes to entropy as well as thermal properties, whereas its temperature dependence is rarely reported for MgH2. Here, vibrational spectra of MgH2 are detected by means of Raman scattering between room temperature and the critical temperature of significant dehydrogenation. The laser power is changed, and the localized sample temperature in the irradiated region is evaluated according to the bandshift of the incorporated carbon with MgH2. With increasing temperature, the frequency for the B1g mode increases, while phonon softening is exhibited for both Eg and A1g modes. It is found that quasiharmonicity decides the thermal frequency shifts for Raman-active vibrations. Phonon–phonon interactions result in significant phonon broadenings for B1g and Eg modes. By contrast, a decreasing line width of the A1g phonon as a function of temperature is observed, possibly arising from the electron–phonon coupling for the A1g mode in MgH2.

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Raman scattering study of α-MgH2 and γ-MgH2

Cited by 13 publications

References 13 publications

Tribochemical Decomposition of Light Ionic Hydrides at Room Temperature

Tribochemical Decomposition of Light Ionic Hydrides at Room Temperature

Phase Stability, Phase Mixing, and Phase Separation in Fluorinated Alkaline Earth Hydrides

Temperature-Dependent Lattice Vibration of Magnesium Hydride

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