Hydrogen adsorption on L12-Al3X(X = Zr, Sc) surface and its diffusion in the bulk: A first-principles study

Abstract

To understand the interaction between hydrogen(H) and intermetallics of L12-Al3Zr and Al3Sc, the adsorption stability and diffusion of hydrogen in the bulk were investigated from first-principles. It is found H can adsorb on L12-Al3Sc(111) and Al3Zr(111) surfaces spontaneously, and the fcc hollow site that co-surrounded by Sc(or Zr) and Al atoms was determined to be the most preferred, whereas the adsorption of H2 on these surfaces was detected energetically unfavorable. Meanwhile, H adsorption tends to stabilize the L12-Al3Sc(111) surface, and when the adsorbed hydrogen coverage on L12-Al3Sc(111) and Al3Zr(111) surfaces exceeds 25%, H2 molecules may form. Additionally, despite the thermodynamically unfavorable of interstitial H in these two intermetallics, interstitial H in tetrahedral of L12-Al3Sc is found relatively preferred, and the local rich in Sc is help to trapping hydrogen, also, the hydrogen in L12-Al3Zr is found to prefer interstitial in regions with higher Zr concentrations. Moreover, the diffusion of H in L12-Al3Zr or L12-Al3Sc are found both favor to diffusion through the tetrahedral to the neighbor octahedral, and the diffusion of hydrogen in L12-Al3Zr is determined sensitive to Zr concentration along the diffusion path, in this regard, the effect of Sc concentration in the diffusion path is limited.