Ternary Cobalt-Iron Phosphide Nanocrystals with Controlled Compositions, Properties, and Morphologies from Nanorods and Nanorice to Split Nanostructures

Structural phase-controlled formation of binary Co2P and CoP nanocrystals is achieved by reacting cobalt(II) oleate with trioctylphosphine. In the absence of oleylamine, Co2P nanowires are formed at both 290 and 320 degrees C. In the presence of oleylamine, Co2P nanorods are formed at 290 degrees C, and CoP nanorods are formed at 320 degrees C. With the simultaneous reaction of iron(III) oleate and cobalt(II) oleate with trioctylphosphine in the presence of oleylamine, ternary Co2P-type cobalt-iron phosphide nanostructures are produced at both 290 and 320 degrees C, corresponding to rice-shaped Co1.5Fe0.5P nanorods and split Co1.7Fe0.3P nanostructures, respectively. The controlled incorporation of iron into cobalt phosphide can alter the magnetic properties from paramagnetic binary Co2P to ferromagnetic Co2P-type ternary cobalt-iron phosphide nanostructures. Meanwhile, the time-dependent morphological evolution from small nanodots/nanorods, through seeded growth to unique split nanostructures is demonstrated in one-pot reaction at 320 degrees C.