The Selenization and Pyritization of Palladium Nanocrystals

Binary and ternary palladium selenides form many different compositions and polymorphs that are host to unique electronic and magnetic phenomena such as superconductivity, exotic spin behavior, and axis-dependent conduction polarity. The development of solution-phase routes toward nano- and micrometer-scale morphologies of these compounds would facilitate future explorations of these properties in this size regime. The selenization of colloidal metal nanocrystals is a useful strategy for preparing metal selenide nanomaterials, but it has not yet been explored to form selenium-rich palladium selenide phases. Here, we demonstrate the preparation of parallelepiped-shaped particles of the metastable, monoclinic PdSe₂ (M-PdSe₂) phase and well-faceted, octahedral-shaped particles of the pyrite Fe_0.5Pd_0.5Se₂ phase via this method. We show that the reaction of Pd nanocrystals with Na₂Se₂ leads to the formation of amorphous PdSe_x nanoparticles as an intermediate, before conversion to M-PdSe₂ (selenization), or Fe_0.5Pd_0.5Se₂ when also in the presence of Fe²⁺ (pyritization). These findings provide a better understanding of palladium nanocrystal selenization pathways and how they can be further developed for the preparation of ternary metal chalcogenide phases.