Thermochemical investigations in the system Cd-Gd.

Vapour pressure measurements were performed in terms of a non-isothermal isopiestic method to determine vapour pressures of Cd in the system Cd-Gd between 693 and 1045 K. From these results thermodynamic activities of Cd were derived as a function of temperature for the composition range 52-86 at.% Cd. By employing an adapted Gibbs-Helmholtz equation, partial molar enthalpies of mixing of Cd were obtained for the corresponding composition range, which were used to convert the activity values of Cd to a common average sample temperature of 773 K. The relatively large variation of the activity across the homogeneity ranges of the phases CdGd and CdGd indicates that they probably belong to the most stable intermetallic compounds in this system. An activity value of Gd for the two phase field CdGd+L was available from literature and served as an integration constant for a Gibbs-Duhem integration. Integral Gibbs energies are presented between 51 and 100 at.% Cd at 773 K, referred to Cd(l) and α-Gd(s) as standard states. Gibbs energies of formation for the exact stoichiometric compositions of the phases CdGd, CdGd, CdGd and CdGd were obtained at 773 K as about -19.9, -21.1, -24.8, and -30.0 kJ g atom-, respectively.