Synthesis and Characterization of Discrete FexNi2–xP Nanocrystals (0 < x < 2): Compositional Effects on Magnetic Properties

Abstract

Ternary FexNi2–xP (0 < x < 2) phases exhibit a range of useful properties that can be augmented or tuned by confinement to the nanoscale including hydrotreating catalytic activity for small x and near-room temperature ferromagnetism for high x. In this work, a solution-phase arrested-precipitation method was developed for the synthesis of FexNi2–xP over all values of x (0 < x < 2). The synthesis involves preparation of Ni–P amorphous particles, introduction of the Fe precursor to form amorphous Fe–Ni–P particles, and high-temperature conversion of Fe–Ni–P particles into crystalline ternary phosphide nanocrystals. The ternary FexNi2–xP nanocrystals crystallize in the hexagonal Fe2P-type structure, and the morphology of the nanocrystals showed a distinct compositional dependence, transitioning from about 11 nm diameter spheres to rods with aspect ratios approaching 2 as the Fe fraction is increased (x ≥ 1.2). Lattice parameters do not follow Vegard’s law, consistent with Mossbauer data showing preferential ...