Hydrogenation properties of shape memory Ti(Ni,Pd) compounds

The effect of Pd substitution on the crystal structure and hydrogenation properties of TiNi compound has been investigated. Ti(Ni,Pd) are pseudo-binary compounds. The unit-cell volumes of B2 (Austenite) and B19 (Martensite) structures linearly increase with Pd substitution in Ti1.04Ni0.96−xPdx samples. The hydrogenation properties of Pd-substituting Ti(Ni,Pd) compounds are not affected by the crystal structure of the parent compounds. For all samples, hydrogen absorption occurs without showing any clear plateau pressure in Pressure-Composition-Isotherm (PCI) curves. All hydrided samples crystallise in the tetragonal I 4/mmm space group. At 6 MPa of hydrogen pressure and T = 423 K, the hydrogenation capacity of Ti(Ni,Pd) compounds reaches 1.52 hydrogen atoms per formula unit (H/f.u.) for x = 0.1 and then gradually decreases with Pd content down to 0.93 H/f.u. for x = 0.5. Ti1.04Ni0.86Pd0.10 sample yields a discharge capacity of 148 mAh/g at C/5 regime when used as negative electrode in Ni-MH battery. The hydrogenation properties of Pd-substituting Ti(Ni,Pd) compounds are discussed in detail by comparison with previous studies on Zr substituting, (Ti,Zr)Ni compounds.

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► Ti(Ni,Pd) compounds behave as pseudo-binary compounds.
► Their hydrogenation properties are not affected by the martensitic transformation.
► All Ti(Ni,Pd) hydrides crystallize in I4/mmm tetragonal symmetry.
► Hydrogenation capacity decreases with Pd content in Ti(Ni,Pd) compounds.
► Electronic effects probably dictate the hydrogenation properties of Ti(Ni,Pd) compounds