Transcript Document

Crystal structure determination
and space groups
H. K. D. H. Bhadeshia
32 point groups
14
Bravais
Lattices
space groups locate atoms within a cell:
help solve unknown structure
14 Bravais
lattices
7 crystal
systems
230
space
groups
32 point
groups
a
axial glide
Cuprite
P
42
y
x
Pn
diagonal
glide
parallel to
(100)
Centre of
symmetry at
height 3/4
centre of symmetry
mirror
triad
Caesium chloride
determine unit cell by diffraction to
be cubic-P
how many atoms per unit cell?
space group of CsCl?
location of atoms?
36 space groups
possible
1/4
3/4
1/4
3/4
1/4
3/4
1/4
1/4
3/4
1/4
Lattice: face-centred cubic
Motif: C at 0,0,0 C at 1/4,1/4,1/4
3/4
1/4
1/4
3/4
Lattice: face-centred cubic
Motif: Zn at 0,0,0 S at 1/4,1/4,1/4
tetragona
l
space group diagram
Z. anorg. allg. Chem., 552: 69–80. doi: 10.1002/zaac.19875520907
Assignment
Draw an accurate stereographic projection of a
cubic crystal, and mark on it the poles of the form
100, 110 and 111.
Without measuring angles, but using vector
addition, mark accurately, poles of the form 112
Ensure that the method you use is clear.