Drastic changes of electronic, magnetic, mechanical and bonding properties in Zr2Co by hydrogenation

Hydrogen insertion into Zr2Co intermetallic leading to Zr2CoH5, is shown to bring large effects in the electronic and magnetic structure and chemical bonding properties besides the experimentally evidenced crystal symmetry changes due to hydrogen ordering. From energy–volume equation of state and elastic constants, Zr2CoH5 is identified more cohesive, harder and less ductile than Zr2Co due to the Zr/Co–H interaction. Hydrogen at two sites is contained into Zr4 and Zr3Co tetrahedra and binds with Zr and Co with dominant covalent Co–H. Within square pyramidal CoH4 motifs non bonding Co-dz2 polarize magnetically leading to ferromagnetic ground state contrary to non-magnetic binary intermetallic.

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► Zr2CoH5 structure derives from Zr2Co but shows original electronic structure.
► H binds within Zr/Co polyhedral but square pyramidal CoH4 have strongest Co–H bonds.
► Apical Co dz2 orbital responsible for small Co moment and ferromagnetic ground state.
► Zr2CoH5 is more cohesive, harder, and less ductile than Zr2Co.