Lesson 2, Topic 7
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Hexagonal Lattices

Abdulaziz July 26, 2020
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Closed Packed Structure

In 2D, close packed layers is the most efficient way of packing equal sized spheres.

i.e. the maximum possible packing for 2D.

Can stack close packed (c.p.) to give 3D structures.

3D Closed Packed Structure

First layer is A (blue) and second layer is B (red).

Third layer, there are two possibilities:

  1. Can have A position again (blue). This leads to the regular sequence
    …ABABABA…..Hexagonal close packing (hcp)
  2. Can have layer in C position (green), followed by the same repeat,
    to give …ABCABCABC… Cubic close packing (ccp)

Difference between hexagonal closed packed (hcp) and cubic closed packed (ccp) structures