Electronic and structural influence of Ni by Pd substitution on the hydrogenation properties of TiNi

In Ti (Ni,Pd) compounds, the hydrogen capacity and the stability of their hydrides decreases when Ni is partially substituted by larger in size Pd atoms. To understand this peculiar behaviour, the crystal structure of TiNi1−xPdxDy (x=0.1, 0.3 and 0.5) deuterides and the stability of TiNi1−xPdx (0≤x≤0.5) intermetallics and their hydrides have been investigated by both neutron diffraction experiments and Density Functional Theory (DFT) calculations. Neutron diffraction shows that at x=0.1 and 0.3, deuterium absorption induces tetragonal distortion in intermetallics sublattice whereas at x=0.5 the cubic symmetry is preserved. The structural properties and the heat of formation of TiNi1−xPdx (0≤x≤0.5) intermetallics and their hydrides have been determined by DFT. These results show that Pd substitution increases the stability of the intermetallics and decreases the stability of the hydrides, which confirms the rule of reverse stability.

Crystal structure of Ti(Ni,Pd)Hy hydrides in the I4/mmm space group Figure optionsDownload as PowerPoint slideHighlights
► Neutron Diffraction and DFT calculations have been done on TiNi1−xPdxHy compounds.
► Electronic effect of Pd substitution governs the hydrogenation properties in TiNi.
► The rule of reverse stability in intermetallics/hydrides is observed with Pd substitution.
► The hydrogen atoms in the I4/mmm structure prefer to occupy the 16n site.