Mischungsverhalten von Palladiumlegierungen des Zwischengittertyps und des Substitutionsgittertyps

Abstract

A close analogy is shown to exist between the excess potential of an interstitial solute, such as hydrogen in palladium, and the difference of the excess potentials of the components of a substitutional alloy, such as silver/palladium. The deviations from ideal behaviour of both systems can be interpreted in terms of a filling up of the 4d- and 5s-electron bands and in terms of an elastic lattice distortion. In the case of palladium alloys, a separation into the two parts is possible, because the Fermi energy rises only negligibly as the valence electrons of silver or hydrogen enter the 4d-band with its high density of states. At low silver or hydrogen concentration, the excess potentials can thus be entirely attributed to the elastic interactions. According to measurements of the palladium activities by Schmahl, a misfit energy of 950 cal/mole is estimated for an alloy of 50% silver at 700°C. In addition, an energy of attraction of - 660 cal per mole pairs and a pair surplus of 4% above the random number of pairs is obtained. The density of states in the 5s-band is calculated to be 0.9 electrons per eV, in good agreement with the value from hydrogen absorption measurements.