The absorption and diffusion of carbon in Pd and Pd-based alloys could be important in applications of these materials as catalysts or membranes, but little was known about these processes. First-principles calculations were used to characterize the absorption of C in pure Pd and PdM alloys with M=Ag, Au, and Cu. The calculations showed that the preferred configuration of C in Pd was as an interstitial atom; effects from Pd vacancies were minimal and substitutional sites were much less favourable. When the effects of thermal lattice expansion were included, the calculations predicted C diffusivities in good agreement with experimental data, which was only available for elevated temperatures. Characterizing the binding energy and hopping energies of interstitial C in terms of lattice expansion or contraction was also a useful way to understand the effect of small amounts of M=Ag, Au, or Cu in PdM alloys. Also examined were the properties of interstitial C in Pd77.7Ag22.3. The calculations predicted that the diffusivity of C in this alloy was two to three orders of magnitude lower than in pure Pd.

First-Principles Evaluation of Carbon Diffusion in Pd and Pd-Based Alloys. C.Ling, D.S.Sholl: Physical Review B, 2009, 80[21], 214202