Interaction between interstitial-interstitial and interstitial-substitutional solute atoms in d-band metals

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Abstract
The electronic contribution to the interaction energy between interstitial solute atoms (I-I interaction) in transition metals is investigated within the tight-binding approximation. The theoretical method used in this study closely parallels that developed by Einstein and Schrieffer for the adatom interaction. The method permits us to study the solution of the gas atom in the octahedral sites as well as in the tetrahedral sites and also allows us to investigate the interaction between the interstitial and substitutional solute atoms (I-S interaction). Calculations have been carried out as a function of band filling, solute atom energy level, an impurity potential matrix element V0 on the substitutional atom site, and a général hopping potential V a between an interstitial atom and the nearest neighbour host atoms. The numerical results generally indicate the importance of the electronic contribution to the interaction énergies (both I-I and I-S interaction). Under reasonable conditions, our simple model of the I-S interaction is shown to agree well with the experimental data for Fe-based ternary alloys containing the simple gas atoms such as N or C. The angular position dependence of the I-I interaction energy is often weak and the possibility of the interstitial condensation (α-α' phase transition) observed in a Nb-H system is discussed. Contact is also made with the solute (I-I) interaction based on the elastic theory

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