Drastic changes in the electronic and magnetic structures of hydrogenated U2Ti intermetallic from first principles

• U–U pairs in U2Ti provide it the largest cohesive energy versus UTi2 and UT.
• H insertion destabilizes U2Ti with anisotropic expansion and weakens Ti–U bonding.
• Iono-covalent character brought by hydrogen from (Ti,U)→H charge transfer.
• Strong localization DOS(U2TiH3) of out-of-plane f orbitals with magnetic instability.
• Resulting ferromagnetic U2TiH3 versus non-magnetic U2Ti.

Based on DFT calculations, hydrogen insertion in U2Ti intermetallic with AlB2-type structure leading to U2TiH3 with sites identified from energy discrimination between different hypotheses is found to decrease the cohesive energy through weakening of the Ti–U bonds, to expand the lattice along c hexagonal axis due to strong U–U in-plane bonding and to induce iono-covalent character with H−0.65. The anisotropic volume expansion involves a strong localization of out-of-plane uranium fz3–3zr2 orbitals leading to developing a magnetic moment on uranium in a predicted ferromagnetic ground state, opposite to non-magnetic intermetallic.

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