Structural and Mössbauer spectroscopy characterization of bulk and nanostructured TiFe_0.5 Ni_0.5/graphite compounds and their hydrides

The structural and hyperfine properties of bulk TiFe_0.5Ni_0.5 intermetallic and ball-milled TiFe_0.5Ni_0.5/graphite compounds and their hydrides have been studied. The bulk and nanostructured TiFe_0.5Ni_0.5 compounds crystallize in the cubic crystal structure of CsCl (B2). After hydrogenation, the formation of hydrogen-poor phase (∝-phase) and hydride phase (β-phase) have been determined for the bulk compound. However, the formation of the ∝-phase and the hydrogen-richest phase (γ-phase) and other secondary phases have been determined for the ball-milled TiFe_0.5Ni_0.5/graphite sample. It has been determined that the ball-milled TiFe_0.5Ni_0.5/graphite sample presents a large amount of the γ-phase which indicates that the presence of graphite nearby nanostructured intermetallic grains enhances the absorption of hydrogen. Mossbauer results are consistent with the structural results. Meanwhile, no significant changes in the isomer shift (IS) value has been determined for the α-phase with respect to the intermetallic compound, a strong increase in the IS value has been determined for the β- and γ-phases with respect to the ∝-phase. That increase indicates a decrease of the s-electron density at the Fe nuclei due to the charge transfer from the metal to the nearby hydrogen atoms