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Diamond Lattice Question

  1. Jan 16, 2009 #1
    1.Hey!

    I dont get the solution to the following question so I am hoping someone can explain!

    Ok so, the question is we have Silicon, which I have read has a DIAMOND LATTICE structure.
    Which basically seems to mean two face centered cubes come together. Now I need to calculate the VOLUME DENSITY of ATOMS. I know the lattice constant ex. 5.4 x 10^-10 m

    Now From my knowledge: fcc in 3d has 1/8th of an atom on each of the 8 corners of the cube. And has also has 1/2 of a atom on each of the 6 faces. That makes a total of

    1/8*8 = 1
    1/2*6 = 3
    --------------
    4 atoms in total

    Now the solution says there are somehow 8 atoms. Im assuming there are 8 because it is a diamond lattice structure and so there are 2 cubes meaning 4 x 2 = 8 atoms..first is this assumption correct?



    if that is correct then when they calculate the volume they use

    (5.4 x 10^-10)^3 = I THOUGHT THIS WAS THE VOLUME OF ONLY ONE CUBE....:O..

    answer somehow is

    atom density = 8/ (5.4 x 10^-10)^3

    HELP!!!!!!!!

    why did they use 8 atoms and why did they use that volume for only one cube if the 8 atoms come from fcc cubes!!!

    please help!
     
  2. jcsd
  3. Jan 18, 2009 #2
    ok i figured it out after some research ..
     
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