Electron microscopy
  
P63/mmc (194) space group
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Table 3026a. P63/mmc (194) space group.

Name in the International Tables for Crystallography
 P63/mmc
Lattice type
 P
Patterson space group
 191
Point group
 6/mmm
Crystal system
 Hexagonal (HCP)
6/mmm
Number of symmetry operators
 24
d-spacing ratios of allowed Bragg reflections
 1, √(4/3), √(4/R2), √(4/3+1/R2), √(4/3+4/R2), √4, ... (R=1.6)
Asymm
 0≤ x ≤ 2/3 and 0 ≤ y ≤ 2/3 and 0 ≤ z ≤ 1/4 and x ≤ 2 y and y ≤ min(1-x,2 x)
Symmetry (atomic coordinates)
X, Y, Z; -Y, X-Y, Z; Y-X, -X, Z; -X, -Y, 1/2+Z; Y, Y-X, 1/2+Z; X-Y, X, 1/2+Z; Y, X, -Z; X-Y, -Y, -Z; -X, Y-X, -Z; -Y, -X, 1/2-Z; Y-X, Y, 1/2-Z; X, X-Y, 1/2-Z; -X, -Y, -Z; Y, Y-X, -Z; X-Y, X, -Z; X, Y, 1/2-Z; Y-X, -X, 1/2-Z; -Y, X-Y, 1/2-Z; -Y, -X, Z; Y-X, Y, Z; X, X-Y, Z; Y, X, 1/2+Z; X-Y, -Y, 1/2+Z; -X, Y-X, 1/2+Z.
0001:1 = 2n; hkil: none; hh2hl: 1 = 2n; hh01: none
Crystal examples
 MgZn2: 2 Zn at 0, 0, 0 and 0, 0, 1/2; 4 Mg at 1/3, 2/3, z; 2/3, 1/3, z + 1/2; 2/3, 1/3, -z and 1/3, 2/3, -z + 1/2; 6 Zn at x, 2x, 1/4; -2x, -x, 1/4; x, -x, 1/4 and -x, -2x, 3/4. MoS2,

Table 3026b. Lattice constants of typical structures with P63/mmc (194).

Structure
a (nm)
b (nm)
General
 2r (r is metallic radius) (8/3)1/2 a
Be
 0.2286 0.3583
Cd
 0.2979 0.5617
Mg
 0.3209 0.5211
Os
 0.2735 0.4319
Re
 0.2760 0.4458
Ru
 0.2706 0.4282
Ti
 0.2506 0.4679
Zn
 0.2665 0.4947
Zr
 0.3312 0.5148

63 screw axis

Figure 3026. 63 screw axis.

 

 

 

 
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