Layer stacking sequence description and symbols

These structural characteristics can be easily represented by using specific codes and symbols, which can be very useful for a compact presentation and comparison of the structural features of several structures. Many different notations have been devised to describe the stacking pattern (for a summary see Parthe 1964, Pearson 1972). A few of them will be presented here. 

As an introduction to this point we consider Figs 3.19 and 3.20 where typical simple close-packed structures are shown and described as built from the 

The sequence ABCABC... having a cubic symmetry is shown in Fig. 3.21. It is the cubic (face-centred cubic) close-packed structure, also described as cF4-Cu type structure. 

A more complete representation of different layer sequences, which can be used not only for the description of close-packed structures, may be obtained by using 

The symbol Cu, Cu Cuy, on the other hand, represents the cubic Cu structure as a stacking sequence of triangular layers viewed along the direction of the unit cell diagonal, which is perpendicular to the layers themselves. 

---