This is an archive copy of the IUCr web site dating from 2008. For current content please visit https://www.iucr.org.

(a) Ramsdell`s notation⁸

Close-packed structures can be designated by specifying the total number of layers in the hexagonal unit cell followed by the letter H , R or C to indicate the lattice type. Thus a symbol nH represents a structure with n layers in the primitive hexagonal unit cell while mR denotes a structure whose primitive lattice is rhombohedral and contains m layers in its hexagonal unit cell. In order to distinguish structures with same lattice type as well as the same repeat period along c , subscripts a , b , c or 1, 2, 3 are often used. This notation is applicable to all close-packed structures but it does not reveal the actual arrangement of the layers in the unit cell.

Copyright © 1981, 1997 International Union of Crystallography