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 add centres 230 space groups microscopic symmetry 7 crystal systems 32 point groups macroscopic symmetry
a axial glide
Cuprite
P 42
x y diagonal glide parallel to (100) P n
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
Lattice: face-centred cubic Motif: C at 0,0,0 C at 1/4,1/4,1/4 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
Lattice: face-centred cubic Motif: Zn at 0,0,0 S 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
tetragonal
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.