CHEMICAL-BINDING ENERGIES OF POINT-DEFECTS IN PALLADIUM DOPED WITH HYDROGEN AND D-IMPURITIES

Using an extra-orbital model within a generalized ″spd″ tight-binding approximation, the chemical binding energy of a pair of hydrogen atoms in palladium within the infinite dilution limit is calculated finding that clusters of hydrogen cannot form in accordance with inelastic neutron scattering data in alpha -palladium hydride. The strong repulsive interaction between a pair of hydrogen impurities at distance a, where a is the host lattice parameter, seems to be related to the presence of an intermediate metallic site between the two impurities. Also determined were the chemical binding energies between a hydrogen atom and d substitutional impurities and the results are discussed in relation with recent Moessbauer experiments. The chemical binding energy between two d impurities in palladium is calculated and compared with experimental data on the enthalpy of formation.