Thermodynamic modeling of the Pd-S system supported by first-principles calculations

Sulfur poisoning of PdCu membrane alloys has promoted new alloy development that requires quantitative understanding of the thermodynamics of the Pd-Cu-S system. This study attempts to develop a self-consistent thermodynamic description of the Pd-rich Pd-S binary system using the CALPHAD approach, based on available phase equilibrium information and thermochemistry data. The optimized phase diagram and enthalpies of formation agree well with the experimental values and first-principles calculations. The phase stability of this system is further investigated using first-principles calculations, confirming that the five intermetallic compounds reported are stable phases. The present density functional theory (DFT) calculations using various exchange-correlation functionals, pseudo-potentials and settings demonstrate that using the PBEsol functional reproduces the experimental enthalpies and phase stability of S, Pd and Pd-S compounds acceptably, and is able to reproduce the lattice parameters nearly perfectly.