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Diffusivity problems in cubic crystals

  1. Oct 10, 2011 #1
    Hi all:
    I encountered a problem when studying the diffusivity of Li atoms in Si crystals.
    From the text book, it is shown the diffusivity tensor in the cubic crystals (BCC FCC) is a diagonal matrix and the values along different directions are also the same (from the rotational symmetry), which means the diffusivity in the cubic crystal is isotropic. However, for the Si diamond cubic structure, If I pick three directions: {1 1 0}, {1 1 -1},{1 1 2}(not the {100}{010}{001}), the lattice arrangement along different directions are obviously different. Thus how the diffusivity can be the same? The same problem for the BCC and FCC.
    I do not know what the mistake I have for my analysis. Could someone help me? Thank you very much!

  2. jcsd
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