Electron microscopy
 
Pnma/Pbnm (62) Space Group
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The axes of Pnma (62) space group (in the International Tables for Crystallography) can be re-defined so that the space group becomes a non-standard setting Pbnm. However, both Pnma and Pbnm have the exact same symmetry with the axes defined differently.

Table 3013a. Pnma/Pbnm (62) space group.

Name in the International Tables for Crystallography
Pnma (The name indicates a primitive lattice with an n-glide plane perpendicular to the x axis, a mirror plane perpendicular to the y axis, and an a-glide plane perpendicular to the z axis) P
47 mmm
Crystal system
Orthorhombic mmm
Asymm
0 ≤ x ≤ 1/2 and 0 ≤ y ≤ 1/4 and 0 ≤ z ≤ 1
8
Symmetry (atomic coordinates)
X, Y, Z; -X+1/2, -Y, Z+1/2; -X, Y+1/2, -Z; X+1/2, -Y+1/2, -Z+1/2; -X, -Y, -Z; X+1/2, Y, -Z+1/2; X, -Y+1/2, Z; -X+1/2, Y+1/2, Z+1/2
0 k 0: k ≠ 2n
Crystal examples
MnHoO3: Paraelectric perovskite.

Table 3013b lists four different crystals in the same space group (Pnma).

Table 3013b. Four different crystals in space group Pnma.

Crystal Chemical formula Lattice parameters Element
Coordinates
x y z
Baryte or barite BaSO4 a=8.884 Å, b=5.458 Å, c=7.153 Å, α=β=γ=90° Ba 0.1846 0.25 0.1581
S 0.4370 0.75 0.1914
O1 0.5878 0.75 0.1062
O2 0.3192 0.75 0.0515
O3 0.4186 0.9702 0.3190
Barium sulfide BaS a=8.85 Å, b=5.43 Å, c=7.13 Å, α=β=γ=90° Ba1 0.318 0.25 0.3388
S1 0.432 0.25 -0.1386
Chalcostibite CuSbS2 a=6.018 Å, b=3.7958 Å, c=14.495, α=β=γ=90° Cu 0.7478 0.75 0.1724
Sb 0.2260 0.25 0.06333
S1 0.6221 0.25 0.0950
S2 0.1294 0.75 0.1756
Stibnite-bismuthinite solid solution series (Sb,Bi)2S3 a=11.256 Å, b=3.8966 Å, c=11.205, α=β=γ=90° Sb1 0.47868 0.25 0.32581
Bi1 0.47868 0.25 0.32581
Sb2 0.34476 0.75 0.03390
Bi2 0.34476 0.75 0.03390
S1 0.2872 0.25 0.1929
S2 0.5491 0.75 0.1276
S3 0.3746 0.75 0.4410

Figures 3013a-b shows the simulated electron diffraction patterns of the four crystals, listed in Table 3013b, in [100], [010] and [001] zone axes, respectively. From these images, we can have some ideas about the diffraction patterns of different crystals with the same space group. For instance, the d-spacings with similar reflections are different for the four crystals due to the differences between their lattice parameters. Furthermore, the rows of the reflection spots marked by the red arrows, in Figure 3013a, have different intensities among the four different crystals. Note that the darkness of the spots indicates their intensities.

BaSO4
BaS
(a)
(b)
CuSbS2
(Sb,Bi)2S3
(c)
(d)

Figure 3013a. Simulated electron diffraction patterns in in [100] zone axis: (a) BaSO4, (b) BaS, (c) CuSbS2 and (d) (Sb,Bi)2S3.

BaSO4
BaS
(a)
(b)
CuSbS2
(Sb,Bi)2S3
(c)
(d)

Figure 3013b. Simulated electron diffraction patterns in in [010] zone axis: (a) BaSO4, (b) BaS, (c) CuSbS2 and (d) (Sb,Bi)2S3.

BaSO4
BaS
(a)
(b)
CuSbS2
(Sb,Bi)2S3
(c)
(d)

Figure 3013c. Simulated electron diffraction patterns in in [001] zone axis: (a) BaSO4, (b) BaS, (c) CuSbS2 and (d) (Sb,Bi)2S3.

 

 

 

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