The thermodynamics of palladium-based solid solutions containing a noble-metal substitutional solute and hydrogen

A cell model for tenary solid solutions containing a substitutional and an interstitial solute species is considered. The interstitial solute is restricted to cells (interstitial sites) in the f.c.c. solvent lattice in which it has either zero or one nearest neighbor substitutional solute atom. The effects of the dilation of the solvent lattice by the substitutional solute are taken into account in an appropriate manner using the currently limited elastic data available.It is shown that the model is in good accord with the measured partial enthalpies and excess entropies in the Pd-Ag-H system, in which the Ag atoms cause a positive lattice dilation, but not for the case of Pd-Cu-H, where there is a contraction.