Because phase boundaries relate to changes in the organization of matter, such as a change from liquid to solid or a more subtle change from one crystal structure to another, this latter usage is similar to the use of "phase" as a synonym for state of matter. However, the state of matter and phase diagram usages are not commensurate with the formal definition given above and the intended meaning must be determined in part from the context in which the term is used.

The phase structure and morphology of the synthesized MNPs are characterized usually by scanning electron microscopy (SEM), high-resolution transmission electron microscope (HR-TEM), and X-ray diffraction (XRD) patterns. For example, Fig. 2.2 shows TEM images of the synthesized Fe@C nanoparticles, the particles exhibit a core/shell structure of magnetic core of Fe coated with carbon shells. HR-TEM images are shown together with the resulting size distribution based on the TEM analysis.