Pnma/Pbnm (62) Space Group

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Pnma/Pbnm (62) Space Group

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)	Lattice type	P
Patterson space group	47	Point group	mmm
Crystal system	Orthorhombic	Laue class	mmm
Asymm	0 ≤ x ≤ 1/2 and 0 ≤ y ≤ 1/4 and 0 ≤ z ≤ 1
Number of symmetry operators	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
Forbidden reflections	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
Crystal	Chemical formula	Lattice parameters	Element	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
Barium sulfide	BaS	a=8.85 Å, b=5.43 Å, c=7.13 Å, α=β=γ=90°	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.


(a)	(b)

(c)	(d)

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


(a)	(b)

(c)	(d)

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


(a)	(b)

(c)	(d)

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

Practical Electron Microscopy and Database

An Online Book, Second Edition by Dr. Yougui Liao (2006)

Pnma/Pbnm (62) Space Group