Universal Features of Hydrogen Absorption in Amorphous Transition-Metal Alloys

• Published in: Physical review. B, Condensed matter Condensed matter, 1987-10, Vol.36 (11), p.5784-5797
• Main Authors: Harris, J H, Curtin, W A, Tenhover, M A
• Format: Article
• Language: English
• ISSN: 0163-1829
• DOI: 10.1103/PhysRevB.36.5784

It is proposed that all A sub 1--x B sub x glasses (where A (B) is a late (early) transition metal) are structurally isomorphic, chemically random alloys which store hydrogen in tetrahedral interstitial sites A sub 4--n B sub n (in decreasing order n = 4,3,2,...). The maximum absorbed H-to-metal atomic ratio within each type of interstitial site is 1.9( exp 4 sub n )x exp n (1--x) exp 4--n (( exp 4 sub n ) = 4/n(4--n)) independent of alloy and temperature. The chemical potential as a function of H concentration within a single site type n is also independent of composition and temperature. The only nonuniversal feature is the dependence of the typical site energies E sub n of the type-n sites on the A and B atoms, which may, however, be estimated from crystalline hydride properties. This model agrees with electrochemical measurements of H 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. It is shown theoretically that infinite near-neighbor H--H 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. 30 ref.--AA