Page 62 - Microsoft PowerPoint - lecture1.ppt

2.4 More complex structures

Oxides: Spinel (MgAl O )
2
4

Crystal data
Formula sum MgAl O 4
2
Crystal system cubic

Space group F d -3 m (no. 227)
Unit cell dimensions a = 8.0625(7) Å

Z 8

Atomic coordinates

Atom Ox. Wyck. x y z Diamond Document
Mg1 +2 8a 0 0 0

Al1 +3 16d 5/8 5/8 5/8

O1 -2 32e 0.38672 0.38672 0.38672 Diamond Document

Structural features:
Structural features:
• distorted CCP of O
• Mg in tetrahedral holes (25%), no connection of tetrahedra

• Al in octahedral holes (50%), common edges

• Inverse spinel structures Mg Al 2OH O → In (Mg, In) O 4
TH
OH
4
TH
• Application: ferrites (magnetic materials)