Magnetic Behaviors of Mg- and Zn-Doped Fe3O4 Nanoparticles Estimated in Terms of Crystal Domain Size, Dielectric Response, and Application of Fe3O4/Carbon Nanotube Composites to Anodes for Lithium Ion Batteries

摘要

Magnesium (Mg)-doped Fe3O4 nanoparticles represented as MgxFe3-xO4 (0 < x = 1) were analyzed in comparison with zinc (Zn)-doped Fe3O4, MgxFe3-xO4 . Magnetization versus applied magnetic field for MgxFe3-xO4 particles provided the maximum saturation magnetization (Ms) with 69.37 emu/g at x = 0.1 as superparamagnetism, while the Ms by Zn-doping was 80.93 emu/g at x = 0.2. The crystal unit volume (Vc) by Mg doping at x <= 0.5 was constant, but the crystal size decreased with increasing x. Doping beyond x = 0.6 provided small amorphous power aggregates which offer universal dielectric response, implying a highly disordered system. In contrast, the Vc by Zn doping expanded up to x = 0.4 as the acceptable limit, which was attributed to the large difference between doping ion radius and replaced Fe3+ ion radius. On the other hand, the MgxFe3-xO4 (0 = x < 0.6) and MgxFe3-xO4 (0 = x = 0.4) formed by a crystal domain were analyzed by a three-circuit model with one normal parallel circuit and two circuits with resistance and a constant-phase element (CPE). The stability of capacity as the anode of lithium ion batteries was investigated for the composites prepared by adhering Mg2+, Zn2+, and Fe3+ on the sidewalls of as-modified multiwall carbon nanotubes. Among the ferrite composites, Zn0.2Fe2.8O4 provided the highest capacity with good stability under discharge and charge cycles.