Hydrogen induced site depopulation in the LaMgNi4-hydrogen system
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Jean-Noël Chotard
Abstract
The LaMgNi4-hydrogen system was investigated by in-situ neutron powder diffraction and pressure-composition 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 α-LaMgNi4H0.75 phase forms below 0.01 bar hydrogen pressure and H atoms fill one type of tetrahedral Ni4 interstices. The orthorhombic distorted β-LaMgNiH3.7 phase forms at about 3 bar hydrogen pressure and H atoms fill both tetrahedral LaNi3 and triangular bi-pyramidal La2MgNi2 interstices. Interestingly, tetrahedral Ni4 interstices are no longer occupied. Finally, the most hydrogen rich γ-LaMgNi4H4.85 phase forms above 20 bar. It has again cubic symmetry and H atoms continue to occupy triangular bi-pyramidal La2MgNi2 interstices while filling a new type of tetrahedral Ni4 interstices that are neither occupied in the α- nor in the β-phase. The tetrahedral LaNi3 interstices occupied in the β-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.
© by Oldenbourg Wissenschaftsverlag, Geneve, Germany
Articles in the same Issue
- Editorial: Hydrogen Storage Materials
- Solving crystal structures of metal and chemical hydrides
- Pair Distribution Functions and Reverse Monte Carlo modelling of disordered metal hydrides
- Coexistence of hydrogen and polyanions in multinary main group element hydrides
- Structures of aluminium-based light weight hydrides
- Light metal borohydrides: crystal structures and beyond
- The structural properties of amides and imides as hydrogen storage materials
- Structural transitions induced by hydrogen absorption in metallic hydrides
- Crystal chemistry and metal-hydrogen bonding in anisotropic and interstitial hydrides of intermetallics of rare earth (R) and transition metals (T), RT3 and R2T7
- Hydrogen induced site depopulation in the LaMgNi4-hydrogen system
- The nature of deuterium arrangements in YD3 and other rare-earth trideuterides
- The crystal structure of α-MgD2 under high pressure by neutron powder diffraction
Articles in the same Issue
- Editorial: Hydrogen Storage Materials
- Solving crystal structures of metal and chemical hydrides
- Pair Distribution Functions and Reverse Monte Carlo modelling of disordered metal hydrides
- Coexistence of hydrogen and polyanions in multinary main group element hydrides
- Structures of aluminium-based light weight hydrides
- Light metal borohydrides: crystal structures and beyond
- The structural properties of amides and imides as hydrogen storage materials
- Structural transitions induced by hydrogen absorption in metallic hydrides
- Crystal chemistry and metal-hydrogen bonding in anisotropic and interstitial hydrides of intermetallics of rare earth (R) and transition metals (T), RT3 and R2T7
- Hydrogen induced site depopulation in the LaMgNi4-hydrogen system
- The nature of deuterium arrangements in YD3 and other rare-earth trideuterides
- The crystal structure of α-MgD2 under high pressure by neutron powder diffraction
