Machine learning potentials for hydrogen absorption in TiCr2 Laves phases

P Kumar and F Körmann and B Grabowski and Y Ikeda, ACTA MATERIALIA, 297, 121319 (2025).

DOI: 10.1016/j.actamat.2025.121319

The energetics of hydrogen absorption in C15 cubic and C14 hexagonal TiCr2Hx Laves phases is investigated for < x <= 6 with density functional theory (DFT) and machine learning interatomic potentials (MLIPs). The MLIPs are trained with configurations generated through a series of active-learning schemes. Basin-hopping Monte Carlo (BHMC) simulations based on the MLIPs predict minimum-energy hydrogen configurations, along with enthalpies of formation and hydrogen orderings. The obtained phase transformations at 0 K agree well with the experiments at low temperatures. The hydrogen solubility limits in the low-concentration alpha phases at 0 K are predicted to be x = 1.0 and x = 1.5 for the C15 and the C14 phases, respectively. At these concentrations, C15 TiCr2H shows the Cc monoclinic symmetry, while C14 TiCr2H1.5 shows the Ama2 orthorhombic symmetry, both of which have not been reported for this system. The first and the second hydride phases, i.e., beta and beta ', at 0 K are found around x = 3 and x = 4, respectively, for both the C15 and the C14 phases. In the second-hydride beta ' phases, C15 TiCr2H4 shows the I4(1)/a tetragonal symmetry, while C14 TiCr2H4 shows the R<(3)over bar>c rhombohedral symmetry. Hydrogen repulsions are found to extend to edge-sharing interstices, affecting the hydrogen ordering. Furthermore, the 6h(2) A(2)B(2) interstices are found to be energetically substantially more preferable for C14 TiCr2Hx than the other A(2)B(2) interstices at low hydrogen concentrations, influencing the hydrogen-occupation trend.

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