Thermodynamics of Ni richest intermetallics along the rare-earth series

The scope of this work is to present and survey a complete set of thermodynamic properties of the Ni rich part of the Ni/Rare-Earth (RE) systems for the whole rare-earth series. This set of data comes entirely from the emf vs. T experimental measurements obtained from galvanic cells with CaF2 single crystal as electrolyte. In order to calculate correctly the standard enthalpy and entropy of formation of RE2Ni17 intermetallics from the raw experimental data, the evaluation of RE solubility in Ni and stoichiometry of the Ni richest phase have been performed. In the case of Pr, the Ni richest phase has been found to be Pr2Ni13, not yet reported in the Pr-Ni phase diagram, and its thermodynamic properties have been calculated. The value of the thermodynamic activity of RE coexisting between the Ni richest phase and Ni solid solution is reported along the series and related thermodynamic partial excess quantities are also given as electronic and dilatation contributions. The apparent deviations of the standard enthalpy change of intermetallic formation with Eu and Yb from the regular trend obtained in the series are explained very satisfactorily by the divalent valence status of such as elements.