Notice that there are 2 separate choices for the second layer in We then place a second close-packed layer (the gold "B" layer)Ītop the the first, so they nestle into the left-pointing holesĪll spheres are actually the same atom, the colors are to help Notice that this is a close-packed arrangement - there is no way to pack We start with a hexagonal array of spheres (the blue "A" layer). Since theseĬut across the other layers, each layer will contain all three colors.Ī different and better way of looking at this structure focuses on Note that diagonal layers also form along our line of sight. If we stack the cells into a lattice we notice that the atoms formĭiagonal layers - the reason for the colors is to make these stand out. Packing can exceed this efficiency (although there are others with the Name "close packed" refers to the packing efficiency of 74.05%. The unit cell is again shown expanded for visibility.Īctually, the corner atoms touch the one in the center of the face. The unit cell is: Click on the unit cell above to view it rotating. Remember that the atoms are all the same. The reason for the various colors is to help point out how the cells We can think of this cell as being made by inserting another atom intoĮach face of the simple cubic lattice - hence the "face centered cubic" Close Packed Structures CLOSE PACKED STRUCTURESįace Centered Cubic (fcc) or Cubic Close Packed (ccp) These are two different names for the same lattice.
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