Determination of Site Occupancy in the M–Pd–Zn (M = Cu, Ag, and Au) γ‑Brass Phase by CALculation of PHAse Diagrams Modeling and Rietveld Refinement

The Pd–Zn γ-brass phase provides exciting
opportunities
for synthesizing site-isolated catalysts with precisely controlled
Pd active site ensembles. Introducing a third metallic element into
the γ-brass lattice further perturbs the catalytic active site
ensembles. Here, we introduce coinage metallic elements M (M = Cu,
Ag, and Au) into the Pd–Zn γ-brass phase and investigate
the site occupation factors of each element in the γ-brass lattice.
The CALculation of PHAse Diagrams (CALPHAD) modeling approach supported
by energetics predicted by the density functional theory and X-ray
and neutron diffraction with Rietveld refinement were used to identify
the SOF on each Wyckoff site for various M amounts alloyed into the
Pd–Zn γ-brass phase. The present analysis unveils the
strong preference for Pd occupying the outer tetrahedral (OT) site
in the γ-brass lattice, while the coinage metallic elements
tend to substitute for Zn on the octahedral (OH) site. The determination
of site occupancy in the bulk M–Pd–Zn γ-brass
phase provides opportunities to investigate and tailor potential catalytically
active site ensembles in the γ-brass phase materials.