Thermodynamic properties of Pd–Y and Pd–Gd intermetallic phases

Abstract

The Gibbs free energies, enthalpies, and entropies of formation were determined for seven Pd–Y and for six Pd–Gd intermetallic compounds from electromotive force measurements on fluorine concentration cells in the temperature range from 973 to 1073 K using CaF2 single crystals as solid electrolytes. The compound formation in both systems is characterized by extremely exothermic mixing effects. The results are compared with calorimetric data and with the theoretical predictions of the Miedema model. The rise of the activities of Y and Gd over the phase fields of Pd3Y and Pd3Gd is described by a statistical model of disorder. The extraordinary stability of the alloys is attributed to a transfer of valence electrons from the electropositive component to the electron gas of the alloy.