Close-packed structures

Lattice is close-packed, if its packing factor is greater than that of random close packing, 0.87, and is loosely packed if its packing factor is less than that of random loose packing, 0.75.

Ideally packed (δ=1) structures can be represented by the stacking sequence of close-packed layers:

stackingelementary metalsselected alloys
ABhD6h4A3 hcpXYC6v4B4 wurtzite
ABCcOh5A1 fccXYTd2B3 zincblende
ABACchD6h4A3' α-LaXYD6h4B81
ABCBCcchhcD3d3 XYXXYD3d3D519 Al3Ni2

Not ideally packed structures can be obtained by deformations and partitions of the above lattices, here are some examples:

For metal alloys with unequal size ions the diversity of close-packed structures grows. For the case, when the smaller ions fit into the voids of the close-packed lattice formed by the larger ones, see ionic compounds with close-packed sublattice.

ABC notations (see Wikipedia):

Close packing