Rhombohedral Crystal Systems
- Practical Electron Microscopy and Database -
- An Online Book -

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This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

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Table 3548a and Figure 3548 show the rhombohedral crystal systems (in orange) and the schematic illustrations of the rhombohedral lattices, respectively. As indicated in Table 3548a, the structures belonging to the trigonal system can have either a rhombohedral or hexagonal lattice. The rhombohedral lattice are stacked in ABCABC...sequence, while the hexagonal lattice are stacked in AAA...sequence. The trigonal system has the rhombohedral unit cell as an unique feature. In this case, the smallest primitive cell may be chosen with a = b = c, α = β = γ ≠ 90°.

Table 3548a. Rhombohedral crystal systems.

Crystal
family
Crystal
system
Required 
symmetries
of point group
Point 
group
Space 
group
Bravais
lattices
Lattice
system
Hexagonal Trigonal 1 three-fold axis of rotation 5 7 1 Rhombohedral
18 1 Hexagonal
Hexagonal 1 six-fold axis of rotation 7 27

Schematic illustrations of the Bravais lattices of trigonal crystals

Figure 3548. Schematic illustrations of the Bravais lattices of rhombohedral crystals.

Table 3548b. Other characteristics of rhombohedral structures.

Contents
Page
Angles in unit cells page3555
Volume of unit cells page3033
Bravais lattices page4546

 

 

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