The as-synthesized Fe3O4 nanoparticle assemblies can be transformed
easily into either ç-Fe2O3 or R-Fe nanoparticle assemblies
by annealing at different atmospheres. Figure 2E is the XRD pattern
of a red-brown nanoparticle assembly obtained from O2 oxidation
of a black 16-nm Fe3O4 particle assembly at 250 °C. Compared to
Figure 2D, the large-angle peaks in Figure 2E shift slightly to highe