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 °C. In the presence of oleylamine, Co2P nanorods are formed at 290 °C, and CoP nanorods are formed at 320 °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 °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 °C. Splitting nanocrystals: Structural phase‐controlled formation of Co2P, CoP, and Co2−xFexP nanocrystals is achieved by reacting cobalt(II) oleate and/or iron(III) oleate with trioctylphosphine. The controlled incorporation of iron into cobalt phosphide can alter the magnetic properties from paramagnetic binary Co2P to ferromagnetic ternary Co1.5Fe0.5P and Co1.7Fe0.3P nanostructures with rice‐shaped and split morphologies, respectively (see figure).