Nanospheres of a New Intermetallic FeSn5 Phase: Synthesis, Magnetic Properties and Anode Performance in Li-ion Batteries

We synthesized monodisperse nanospheres of an intermetallic FeSn5 phase via a nanocrystal-conversion protocol using preformed Sn nanospheres as templates. This tetragonal phase in P4/mcc space group, along with the defect structure Fe0.74Sn5 of our nanospheres, has been resolved by synchrotron X-ray diffraction and Rietveld refinement. Importantly, FeSn5, which is not yet established in the Fe–Sn phase diagram, exhibits a quasi-one dimensional crystal structure along the c-axis, thus leading to interesting anisotropic thermal expansion and magnetic properties. Magnetization measurements indicate that nanospheres are superparamagnetic above the blocking temperature T B = 300 K, which is associated with the higher magnetocrystalline anisotropy constant K = 3.33 kJ m–3. The combination of the magnetization measurements and first-principles density functional theory calculations reveals the canted antiferromagnetic nature with significant spin fluctuation in lattice a–b plane. The low Fe concentration also leads Fe0.74Sn5 to enhanced capacity as an anode in Li ion batteries.