Interaction between hydrogen and the alloying atom in palladium

Abstract

The interaction energies between interstitial hydrogen and $3d$- as well as $4d$-alloying atoms in Pd were calculated by the use of a first-principles plane-wave pesudopotential method. The calculation results show that almost all the considered alloying atoms are repulsive to hydrogen. For the interaction between H and a noble metal alloying atom that binds weakly to the host atom relative to the host atom itself, the traditional elastic model, proposed in the literature to address the interaction between the substitutional and interstitial atoms in metals, works well. However, for the transition metal atom which binds strongly to the host atom, the interaction energy cannot be explained by the traditional chemical/elastic models. We considered that this failure is due to the absence of binding between the alloying and host atoms. We proposed that, for these transition metal alloying atoms, the interaction energy is controlled by a mechanism similar to Miedema's ``reverse stability'' rule, i.e., the larger the binding energy of the alloys, the stronger the repulsion between the alloying atom and H. The calculated interaction energies were compared to the available experimental information.