Lecture 1: Stacking of atoms PHYS 430/603 material Laszlo Takacs UMBC Department of Physics

Two consecutive layers of close packed hexagonal layers of atoms ABC sequence of close packed hexagonal layers of atoms, leading to fcc structure.

Where is the cube in fcc?

Two consecutive layers of close packed hexagonal layers of atoms ABAB sequence of close packed hexagonal layers of atoms, leading to hcp structure.

Seven circles fit together tightly and in only one way on a plane, each neighbor touching each other. This is not true for 13 spheres in 3-d space; the 12 spheres touching the central one do not touch each other and can be arranged in different ways. The lower image is an icosahedron, fcc and hcp are other examples. Space cannot be filled with tetrahedra alone (top.)

The bcc structure. Construction and the closest-packed plane

Interstitial sites in bcc structure

Interstitial sites in fcc structure

The structure of kaolinite, Al2O3  2SiO2  2H2O Lower two layers Top three layers Layers from top: O, OH Al Si O