Universal features of hydrogen absorption in amorphous transition-metal alloys

Abstract

We propose that all A| "B"glas ses [where A (B) is a late (early) transition metal) are structurally isomorphic, chemically random alloys which store hydrogen in tetrahedral interstitial sites A4 "B"(indecreasing order n =4, 3, 2, . . . ). The maximum absorbed hydrogen-to-metal atomic ratio within each type of interstitial site is 1.9(")x"(1 -x)' " [('")=4!In!(4 n-)!] independent of alloy and temperature. The chemical potential as a function of hydrogen concentration within a single site type n is also independent of composition and temperature. The only nonuniversa1 feature is the dependence of the typical site energies E"ofthe type-n sites on the A and B atoms, which may, however, be estimated from crystalline hydride properties. This model agrees with our electrochemical measurements of hydrogen in Ni-Zr, Pd-Ti, and Ni-Ti, predicts total H/M ratios for Ni-Zr and Cu-Ti alloys in excellent agreement with literature gas-phase data over a wide range of compositions and thermodynamic conditions, and is consistent with literature H/M data on other alloys at isolated compositions. %e show theoretically that infinite near-neighbor hydrogenhydrogen interactions (blocking) in a glass dominated by fivefold rings of tetrahedral units predicts the observed x dependence of H/M with a prefactor of 1.9 -2. 1, in excellent agreement with the observed factor of 1.9. This result supports theoretical models of icosahedral ordering in glasses.

Hydrogen Permeable Nb-Based Amorphous Alloys with High Thermal Stability

“…As is reported by Aoki et al, 24) the hydrogen absorption in the NiZr system increased dramatically with Zr addition. Harris et al 25) also reported that hydrogen tends to stay between tetrahedral interstitial sites surrounded by Zr 4 atoms rather than Zr 3 Ni 1 or Zr 2 Ni 2 sites. The increase of hydrogen permeability with Zr addition may also be attributed to an improved hydrogen absorption in the NbNiCoZr system.…”

The Electrochemical Hydrogen Sorption Behaviour of Zr-Cu-Al-Ni Metallic Glasses

“…This means that for glassy Zr-Ni alloys, the tetrahedral interstitial sites which hydrogen may occupy are in the following energy order: Zr 4 < Zr 3 Ni < Zr 2 Ni 2 < ZrNi 3 < Ni 4 . This model was proved to be valid also for ternary glassy alloys such as Zr-Ni-Cu, 6) and it is possible that these interstitial sites exist in the quaternary alloys, e.g. Zr-Cu-Al-Ni.…”

“…Hydrogen has been used as a probe to explore the distribution of interstitial sites in the amorphous phase of these alloys. 4) Hydrogen investigations done on Zr-Ni metallic glasses using neutron scattering, 5) followed by a statistical model for the hydrogen absorption of amorphous LTM/ETM alloys 6) proposed that the lowest energy hydrogen sites are those surrounded by four ETM atoms, so that: E 4 < E 3 < E 2 < E 1 < E 0 , where E n is the energy of hydrogen in A (4−n) B n tetrahedral interstitial sites. This means that for glassy Zr-Ni alloys, the tetrahedral interstitial sites which hydrogen may occupy are in the following energy order: Zr 4 < Zr 3 Ni < Zr 2 Ni 2 < ZrNi 3 < Ni 4 .…”

Inelastic neutron scattering study of the hydrogenated (Zr55Cu30Chuang1, Udovic2, Liaw3 et al. 2011Phys. Rev. B

“…Later, Harris et al 9 proposed a universal model, after reviewing the common features of hydrogen in Ni-Zr, Cu-Ti, Pd-Zr, Rh-Zr, Cu-Zr, and Fe-Ti systems, to describe the behavior of dissolved hydrogen in ETM-LTM amorphous alloys. They suggested the following; First, interstitial sites for hydrogen are tetrahedral, with varying chemical sites.…”