Hydrogen-Induced Phase Transformations In H-Storing Alloys of Zirconium

In situ powder synchrotron and neutron diffraction study of Zr2Ni deuterides

“…It has been pointed out that the c/a-ratio of the deuterium-free intermetallic appears important for the site preference [2]. However, the c/a-ratio only reflects a more important underlying quantity, namely the relative size ratio of the 4b site and the 16l site, r(4b)/r(16l).…”

“…In most cases, the tetragonal symmetry is retained on hydrogenation (or deuteration), e.g. Th 2 AlD 4 (space group I4/mcm) [1], Zr 2 FeD 5 (P4/ncc) [2], Zr 2 CoD 5 (P4/ncc) [3], Nb 2 (Co, Si)D 1.25 (I4/mcm) and Nb 2 (Ni, Si)D 1.35 (I4/mcm) [4]. Zr 2 Ni, which forms hydrides with maximum hydrogen content corresponding to about Zr 2 NiH 5 , is the only known exception.…”

An in situ neutron diffraction study of the thermal disproportionation of the Zr2FeD5 system

“…The phase proportion of Zr 2 FeD 5 does not change significantly until after 280 • C. Initially, the room temperature P4/ncc Zr 2 FeD 5 phase possesses a completely ordered D sublattice, with full occupation of 4b (Zr 4 tetrahedra) and 16g (Zr 3 Fe tetrahedra) sites. The 16g site is one split half of the 32m site in the parent Zr 2 Fe structure, and as discussed in [18], only one half of the original 32m site is occupied with D, which avoids face sharing tetrahedra and short D-D distances. In [30], it is observed that at lower D content, the P4/ncc Zr 2 FeD 5−x phase transforms to the tetragonal I4/mcm Zr 2 FeD 5−x phase, and the D ordering is removed, and partial occupancy of the 32m and 16l (Zr 4 tetrahedra) sites occurs.…”

“…It is reported in [20] that amorphous Zr 2 Fe can absorb a small amount of hydrogen, 0.2-0.7 wt.%H, which increases T cryst by ca. 40 K. Crystalline Zr 2 Fe can absorb deuterium up to a composition of Zr 2 FeD 5 , which possesses a tetragonal unit cell in space group P4/ncc [18]. The crystalline Zr 2 FeH 5 hydride forms part of the greater Zr 2 MHx family (M = Ni, Cu, Co, Fe, etc.…”

“…There exist many quenching techniques, from extremely rapid at 10 6 K/s, such as melt spinning, enabling the production of predominantly bulk amorphous alloys [11], to slower techniques, such as arc melting, typically 10 1 K/s, producing predominantly crystalline alloys. Due to a large gradient of cooling rate between free sample surface (10 1 K/s) and the Cu hearth (up to 10 6 K/s), arc melted samples are typically inhomogeneous, multi-phase [1], and may retain a minor amorphous component [15], which is why arc melted samples are typically flipped and re-melted several times [16][17][18], or post annealed to ensure homogeneity. Amorphous Zr 2 Fe is quite stable, displaying a crystallisation temperature (T cryst ) >700 • C for mechanically alloyed material [10], and an onset of crystallisation of ca.…”