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Solving the "Coloring Problem" in InPd3-xAgx (x = 0-0.7) by Phase Diagrams Modeling and Diffraction Experiments
Nilanjan Roy1,2, Sandip K Kuila1, Jin Li2
1Department of Chemistry, IIT Kharagpur, Kharagpur, WB 721302, India.
None:
A series of InPd3-xAgx (x = 0-1) compositions were synthesized by conventional high-temperature synthesis, and as-synthesized samples were characterized by powder X-ray diffraction experiments. Up to x = 0.7, InPd3-xAgx adopts the ternary substitutional variant of the InPd3 structure (TiAl3-type), when x > 0.7, elemental Ag starts to segregate along with the main phase. Accurate structural characterization in InPd3-xAgx faces a critical challenge due to the narrow X-ray scattering contrast among constituents In, Pd, and Ag and nearly identical neutron scattering lengths of Pd and Ag. To overcome this "coloring problem", a combination of calculation of phase diagrams modeling (CALPHAD) and diffraction techniques (X-ray and neutron) was employed. In the compositional range 0 ≤ x ≤ 0.7, InPd3-xAgx presents a ternary variant of the TiAl3-type structure, where Ag atoms selectively substitute one (the 2b Wyckoff site) of the two Pd sites in InPd3. Notably, in contrast to the isologous InPd3-xCux (x = 0-1) system, Ag substitution does not form an ordered VRh2Sn-type structure at the limiting composition. The distinct site preference in InPd3-xAgx is elucidated by charge population analysis, electronic structure calculations, and orbital-resolved chemical bonding investigations, and the extent of substitution is supported by formation free energy calculations.
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