INTERSTITIAL SITE OCCUPANCIES BY H - A STATISTICAL-MODEL OF BLOCKING EFFECTS AND H-TRANSITION-PROBABILITIES IN FCC BINARY-ALLOYS

Interstitial solid solutions of H in random fcc metal alloys have been examined in detail as far as the nature of interstitial sites and the ir spatial correlations are concerned. Both octahedral and tetrahedral sites have been considered and distinguished on the basis of the atom ic composition and atomic arrangements within their first shell of nei ghbors. The conditional probability q(uu)' of finding a site of type u ' as nearest neighbor of a given site of type u were calculated. Expre ssions for selective blocking factors and occupancy probabilities have been derived for the approximation of the hard-core model, assuming b locking of sites at distances smaller than about 0.21 nm from the occu pied site. The application of the model to the Pd1-yPty system shows t hat H solubility data can be interpreted on the basis of a site-fillin g process. Finally, transition probability factors have been estimated to predict the occurrence of anelastic relaxations.