Page 61 - Microsoft PowerPoint - lecture1.ppt
P. 61
2.4 More complex structures
Oxides: undistorted perovskite (SrTiO )
3
Crystal data
Formula sum SrTiO 3
Crystal system cubic Cuboctahedron
Unit cell
Space group P m -3 m (no. 221)
Unit cell dimensions a = 3.9034(5) Å
Z 1
Atomic coordinates
Atom Ox. Wyck. x y z
Sr1 +2 1a 0 0 0
Ti1 +4 1b 1/2 1/2 1/2
O1 -2 3c 0 1/2 1/2
Structural features:
Structural features:
• filled ReO phase, CN (Ca) = 12 (cuboctaehdron), CN (Ti) = 6 (octahedron)
3
• many distorted variants (even the mineral CaTiO !)
3
• many defect variants (HT-superconductors, YBa Cu O )
7-x
2
3
• hexagonal variants and polytyps
