Copper 4: close-packed layers in the copper unit cell

In a close-packed layer each atom in the bulk is touching six neighbours in the plane of that layer. In the face-centred cubic unit cell, the close-packed layers run perpendicular to the body-diagonals. (The body-diagonals run from one corner to the diagonally opposite corner.) As such they are quite difficult to see, and so in the diagram on the left the close-packed layers in the unit cell are colour-coded. Each cube has four body diagonals (as there are four pairs of diagonally opposite corners) and so the close-packed layers can be shown in any of four orientations. This can be appreciated by rotating the image to the left so that the different corner positions rotate into each other.

By rotating the image on the left so that you are looking down the body diagonal you can appreciate that the blue, green and brown layers are different from each other. The blue atoms, however, are in equivalent positions: they line up with each other from the point of view of the close-packed layers. Since there are three types of close-packed layer before the first type repeats itself, this arrangement is known as ABC packing.

The remaining copper pages take a more advanced approach. Go to page 5 to look at the geometry around a copper atom in the bulk structure.

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