A preliminary study of some “pseudo-AB2AB2” compounds: RENi4MgRENi4Mg with RE=LaRE=La, Ce and Gd. Structural and hydrogen sorption properties

Bobet, Jean-Louis; Lesportes, Pierre; Roquefere, Jean‐Gabriel; Chevalier, Bernard; Asano, Keisuke; Sakaki, Kouji; Akiba, Etsuo

doi:10.1016/j.ijhydene.2006.11.031

Cited by 59 publications

(32 citation statements)

References 11 publications

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“…X-ray powder diffraction (XPD) on a laboratory instrument (Bruker D8 Advance) revealed the presence of quasi single-phase samples that consisted mainly of the known cubic LaMgNi 4 phase [9] and small quantities (<1 wt%) of the hexagonal LaNi 5 phase, but no oxide was identified. Rietveld refinements from X-ray powder diffraction yielded structure parameters for the LaMgNi 4 phase similar to those reported previously [9], except for the cubic cell parameter that was intermediate between those reported (a ¼ 7.17027(1) A, as compared to a ¼ 7.1794(2) A reported in [9] and 7.165(1) A in [11]) and the positional parameter of Ni that was refined rather than fixed (x ¼ 0.6240(1), as compared to x ¼ 0.625(À) in [9]). Before performing in-situ neutron powder diffraction (NPD) and pressure-composition isotherm (PCI) measurements, the samples were activated under dynamic vacuum (3 Á 10 À2 mbar) at 120 C overnight and then charged at 100 C with hydrogen (for the PCI measurement) or deuterium (for the NPD measurement) at pressures of up to 50 bar.…”

Section: Experimental Synthesissupporting

confidence: 80%

Hydrogen induced site depopulation in the LaMgNi₄-hydrogen system

Chotard¹,

Sheptyakov²,

Yvon³

2008

Zeitschrift Für Kristallographie

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Metal hydride structures / In-situ neutron powder diffraction / Pressure-composition-isotherms / Structure-property relation Abstract. The LaMgNi 4 -hydrogen system was investigated by in-situ neutron powder diffraction and pressurecomposition isotherm measurements at 100 C and hydrogen (deuterium) pressures of up 50 bar. The system displays three hydride phases that have distinctly different hydrogen plateau pressures and H atom distributions. The cubic a-LaMgNi 4 H 0:75 phase forms below 0.01 bar hydrogen pressure and H atoms fill one type of tetrahedral Ni 4 interstices. The orthorhombic distorted b-LaMgNiH 3:7 phase forms at $3 bar hydrogen pressure and H atoms fill both tetrahedral LaNi 3 and triangular bi-pyramidal La 2 MgNi 2 interstices. Interestingly, tetrahedral Ni 4 interstices are no longer occupied. Finally, the most hydrogen rich gLaMgNi 4 H 4:85 phase forms above 20 bar. It has again cubic symmetry and H atoms continue to occupy triangular bipyramidal La 2 MgNi 2 interstices while filling a new type of tetrahedral Ni 4 interstices that are neither occupied in the a-nor in the b-phase. The tetrahedral LaNi 3 interstices occupied in the b-phase are empty. Hydrogen induced depopulations of interstitial sites in metal hydrides are relatively rare and consistent with, but not entirely due to, the onset of repulsive H--H interactions at increasing hydrogen concentrations.

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Section: Experimental Synthesissupporting

confidence: 80%

Hydrogen induced site depopulation in the LaMgNi₄-hydrogen system

Chotard¹,

Sheptyakov²,

Yvon³

2008

Zeitschrift Für Kristallographie

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“…Nevertheless, the presence of LaH 3 , which could affect the reaction, is not considered in this thermodynamic calculation. So, the first experimental plateau pressure corresponds to the reaction (4) and the second to the reaction (5). According to reactions (4) and (5), the hysteresis on the first plateau is unexpected.…”

Section: 2mentioning

confidence: 85%

Study of the hydrogenation mechanism of LaCuMg8 ternary phase: The decomposition induces kinetics improvement

Couillaud

Gaudin

Andrieux

et al. 2012

International Journal of Hydrogen Energy

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Kinetic and thermodynamic studyMorphologic effects a b s t r a c tThe hydrogen sorption properties of LaCuMg 8 are investigated. LaCuMg 8 crystallizes in the La 2 Mg 17 structure type with the lattice parameters a ¼ 10.1254(2) Å and c ¼ 10.0751(2) Å .An absorption mechanism in 2 steps was reported earlier: (i) the first step, which is irreversible, induces the decomposition of LaCuMg 8 into an intimate mixture of 3 phases of sub-micronic size (i.e. LaH 3 , MgCu 2 and MgH 2 ); (ii) the second step consists in the reversible absorption of the "LaCuMg 8 activated powder" with kinetics better than for pure magnesium. In order to get a better understanding of the absorption process, it was investigated from thermodynamic, kinetic and morphology points of view. From thermodynamic point of view, the "LaCuMg 8 activated powder" behaves like a mixture. Concerning the kinetics, the activation energy was evaluated at about 65 kJ/mol H 2, using AvramieErofeev model and Arrhenius law. To explain the enhancement of the kinetics, both effects of (i) Mg 2 Cu/ MgCu 2 transformation and (ii) morphology induced by the decomposition have been considered.

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“…In such a case, R A =R B would be equal to 1.34 and the amorphisation should occur according to the Aoki criteria. As no amorphisation is observed, it is demonstrated that the 4a and 4c sites are not randomly occupied by Mg and Y as reported in [22,29]. The criteria defined by Aoki et al are easily applicable for AB 2 compounds but not for pseudo-AB 2 compounds.…”

Section: Article In Pressmentioning

confidence: 79%

In situ X-ray diffraction under H2 of the pseudo-AB2 compounds: YNi3.5Al0.5Mg

Stan

Andronescu

Asano

et al. 2008

International Journal of Hydrogen Energy

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In situ XRD a b s t r a c tThe hydrogenation and dehydrogenation behaviours of the YNi 3.5 Al 0.5 Mg compound were studied by in situ X-ray diffraction under hydrogen pressure and at room temperature. The changes of (i) the lattice parameters, (ii) the crystallite size and (iii) the lattice strain during the sorption process (i.e. along the PC isotherms) were studied. These results indicate that the crystallite size decreases by a factor of 2. The micro deformations increase at first and then tend to almost zero at the end of the sorption cycle. This behaviour is explained in terms of co-existence of the metal (i.e. a phase) and metal hydride (i.e. b phase) phases. The change in crystallinity is consistent with the hydrogen induced amorphisation process existing in a lot of AB 2 compounds. No anisotropic effects can be highlighted on this pseudo-AB 2 compounds in contrary with what could be observed in AB 5 compounds.

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A preliminary study of some “pseudo-AB2AB2” compounds: RENi4MgRENi4Mg with RE=LaRE=La, Ce and Gd. Structural and hydrogen sorption properties

Cited by 59 publications

References 11 publications

Hydrogen induced site depopulation in the LaMgNi₄-hydrogen system

Hydrogen induced site depopulation in the LaMgNi₄-hydrogen system

Study of the hydrogenation mechanism of LaCuMg8 ternary phase: The decomposition induces kinetics improvement

In situ X-ray diffraction under H2 of the pseudo-AB2 compounds: YNi3.5Al0.5Mg

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A preliminary study of some “pseudo-AB2AB2” compounds: RENi4MgRENi4Mg with RE=LaRE=La, Ce and Gd. Structural and hydrogen sorption properties

Cited by 59 publications

References 11 publications

Hydrogen induced site depopulation in the LaMgNi4-hydrogen system

Hydrogen induced site depopulation in the LaMgNi4-hydrogen system

Study of the hydrogenation mechanism of LaCuMg8 ternary phase: The decomposition induces kinetics improvement

In situ X-ray diffraction under H2 of the pseudo-AB2 compounds: YNi3.5Al0.5Mg

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Hydrogen induced site depopulation in the LaMgNi₄-hydrogen system

Hydrogen induced site depopulation in the LaMgNi₄-hydrogen system