A neutron diffraction study of the interstitial sites of deuterium in the A-15 compound Ti3Ir

Hydrogen in Ti3Sb and Ti2Sb: Neutron vibrational spectroscopy and neutron diffraction studies

“…The total D content of the A15-type phase resulting from the refinement corresponds to 2.97(2) D atoms per formula unit of Ti 3 Sb. A partial occupancy of the 24k sites was earlier reported for the Ti 3 Ir deuteride with x > 3 (Ti 3 IrD 3.63 ) [12]. Our present results indicate that D atoms can start to fill the 24k sites at x < 3 (i.e., before the 6d sites are completely filled).…”

“…1. A partial occupancy of the 24k sites in Ti 3 IrD 3.63 [12] and the 16i sites in Nb 3 AuH 2.9 and Nb 3 AuH 4.2 [13] has been confirmed by neutron diffraction measurements.…”

“…Our present results indicate that D atoms can start to fill the 24k sites at x < 3 (i.e., before the 6d sites are completely filled). It should be noted that the positional parameters of D atoms at the 24k sites found for Ti 3 SbD 2.6 at 300 K (0.301, 0, 0.138) differ significantly from those for Ti 3 IrD 3.63 (0.262, 0, 0.148) [12]. This suggests that these positional parameters may depend on the ratio of atomic radii of the elements A and B forming an A15-type compound.…”

“…The first neutron diffraction study of hydrogen sites in an A15-type hydride [4] has revealed that H atoms in Nb 3 SnH 1.0 occupy the 6d positions of the space group Pm3n, i.e., the tetrahedral interstitial sites (coordinated by four Nb atoms) on the faces of the unit cell. These sites appear to be the most attractive for hydrogen in A15-type compounds, and the preferential filling of the 6d sites by H(D) atoms has been reported for Ti 3 SbD x [11], Ti 3 IrD x [12], Nb 3 AuH x [13] and Nb 3 (Al 0.84 Nb 0. 16 )D x [14].…”

“…It should be noted that a possibility of the filling of the 24k sites by hydrogen atoms was not included in the structural model of Ref. [11] (the actual filling of the 24k sites in Ti 3 IrD 3.63 [12] was revealed later). Therefore, in order to understand the structural basis of the fast localized H jump motion in Ti 3 SbH x [16], we have performed a new investigation of the positions of hydrogen atoms in the Ti 3 Sb hydride complemented by the study of the vibrational spectra of H(D) atoms in this system.…”