# Structural study of Y0.88Ni3-xMnx: an approach combining diffraction and computation

Ghofrane Fedlouk, Judith Monnier, L. Laversenne, Lei Lei, Sanliang Ling, Junxian Zhang

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Ghofrane Fedlouk, Judith Monnier, L. Laversenne, Lei Lei, Sanliang Ling, et al. Structural study of Y0.88Ni3-xMnx: an approach combining diffraction and computation. 4ème réunion plénière de la Fédération Hydrogène (FRH2) du CNRS, Fédération Hydrogène (FRH2) du CNRS, Oct 2024, La Grande Motte, France. hal-05004773

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Submitted on 28 Mar 2025

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# Structural study of Y<sub>0.88</sub>Ni<sub>3-x</sub>Mn<sub>x</sub>: an approach combining diffraction and computation

G. Fedlouk<fnref n="1" />, J. Monnier<fnref n="1" />, L. Laversenne<fnref n="2" />, L. Lei<fnref n="3" />, S. L. Ling<fnref n="3" /> and J. Zhang<fnref n="1" />

Metal hydrides, especially those derived from intermetallic compounds, prove to be safe and efficient for hydrogen storage. Among these alloys, AB₃ (A = rare earth and Mg, B = transition metals) compounds are noteworthy for exhibiting interesting characteristics since they have inter-growth structures. These structures correspond to the stacking of two basic units [AB₅] and [A₂B₄] along the crystallographic c-axis. Rare earth based binary AB₃ alloys provide high storage capacities because they contain [A₂B₄] units. For the same reason, they aren't completely reversible [1]. Optimizing and enhancing their hydrogenation properties can be achieved through adjusting the composition via element substitution, which induces structural modifications.

Beside R₂MgNi₉ compounds, which are largely studied (R = rare earth) [1], the YNi₃-xMnₓ alloys have attracted interest due to their Mg-free nature and to their potential applications in various fields, including hydrogen storage. To our knowledge, the structural study on these compounds is unknown.

For the present work, we opted to investigate Y<sub>0.88</sub>Ni<sub>3-x</sub>Mn<sub>x</sub> (x = 0.1; 0.2; 0.3; 0.4; 0.8 and 1) system. The lattice parameters of the AB₃ phase determined by X-ray diffraction do not vary linearly with Mn content which may indicate a non-random occupation of Mn atoms in the structure (Figure 1.a). Due to the limited scattering contrast between Mn and Ni in X-ray diffraction, neutron diffraction is indispensable for accurately determining the precise location of Mn within the structure. By combining the synchrotron and neutron diffractions, the joint refinement demonstrates that at low concentrations, Mn exclusively occupies the Y-site within the [A₂B₄] units and the Ni-site within the [AB₅] units. As the concentration increases, Mn also occupies Ni-sites on the boundary between [A₂B₄] and [AB₅] units (Figure 1.b). The evolution of the lattice parameters is tightly correlated to these variations in Mn-occupancy. To better understand this phenomenon, DFT calculations have been coupled to this advanced structural characterization.

<figure><img src="image_2.png" /><figcaption>Figure 1. a) Evolution of lattice parameters of AB₃ (R) phase in Y<sub>0.88</sub>Ni<sub>3-x</sub>Mn<sub>x</sub> (0.1 ≤ x ≤ 1) alloys as a function of Mn content. b) Mn's occupancy percentage in the main phase AB₃ (R) for all the studied alloys.</figcaption></figure>

**Reference:**

[1] W. Liu, C. J. Webb, et E. Mac A. Gray, « Review of hydrogen storage in AB₃ alloys targeting stationary fuel cell applications », *Int. J. Hydrog. Energy*, **(2016)** vol. 41, no 5, p. 3485-3507.

<footnote n="1">¹ Univ Paris Est Créteil, CNRS, ICMPE, UMR 7182, 2 rue Henri Dunant, 94320 Thiais, France</footnote>

<footnote n="2">² Institut Néel, CNRS, 25 Av. des Martyrs, 38042 Grenoble, France</footnote>

<footnote n="3">³ University of Nottingham Energy Institute, Nottingham, United Kingdom
ghofrane.fedlouk@cnrs.fr</footnote>