Sharp and Diffuse Interfaces

Interfaces may be sharp or diffuse. A sharp interface possesses a relatively narrow core structure with a width close to an atomic nearest-neighbor separation distance. Examples of sharp crystal/vapor and crystal/crystal interfaces are shown in Figs. B.l and B.2. 

On the other hand, a diffuse interface possesses a significantly wider core that extends over a number of atomic distances. A diffuse crystalline/amorphous phase interface is shown in Fig. B.3. Similar structures exist in crystal/liquid interfaces [5]. 

Diffuse crystal/crystal interfaces often appear in systems subject to incipient chemical or structural instabilities associated with phase separation, long-range ordering, or displacive phase transformations [2], Examples of interfaces associated with the first two types are shown in Fig. 18.7. 

2 The number of geometrical degrees of freedom is the number of geometrical parameters that must be specified in order to define the interface. 

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