Connecting Cation Exchange and Metal Deposition Outcomes via Hume-Rothery-Like Design Rules Using Copper Selenide Nanoparticles.

Heterogenous nanomaterials containing various inorganic phases have far-reaching impacts both from the physical phenomena they reveal and the technologies they enable. While the variety and impact of these materials has been demonstrated in many reports, there is critical ambiguity in the factors that lead to major bifurcations in developing these heterostructures, for example, the formation of either mixed metal semiconductors or segregated metal-semiconductor phases. Here, we compare outcomes of independently introducing 5 different metal cations (Au3+, Ag+, Hg2+, Pd2+, and Pt2+) to antifluorite copper selenide (Cu2-xSe) nanoparticles (diameter = 52 ± 5 nm). This suite of metal cations allowed us to control for and evaluate a variety of potentially competing intrinsic system parameters including metal cation size, valency, and reduction potential as well as lattice volume change, lattice formation energy, and lattice mismatch. Upon secondary metal addition, we determined that the transformation of a cubic Cu2-xSe lattice will occur via cation exchange reaction when the change in symmetry to the resulting metal selenide phase(s) preserves mutually orthogonal lattice vectors. However, if the new lattice symmetry would be disrupted further, metal deposition is the likely outcome of secondary metal cation addition, forming metal-semiconductor heterostructures. These results suggest a synthesis design rule that relies on an intrinsic property of the material, not the reaction pathway, and indicates that more such factors may be found in other particle and synthetic systems.