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Solid state-problem with difraction

  1. Oct 6, 2015 #1
    1. The problem statement, all variables and given/known data
    Hi everybody. I am triying to do the next exercice:
    Given a unit cell of Ice X and knowing the positions of the atoms on it, find the expression of the structure factor for a difraction peak as a function of its Miller's index and the atomic form factors fO and fH.

    Will there be a systematic extinction?

    Would there be more extinctions if fO=fH

    2. Relevant equations
    F=Σfi*erjHhkl

    In the ice X, there are two atoms of oxygen (0,0,0) and (0.5, 0.5, 0.5); the atoms of hydrogen are at (1/4, 1/4, 1/4), (3/4, 3/4, 1/4), (3/4, 1/4, 3/4) and (1/4, 3/4, 3/4)

    3. The attempt at a solution

    F=fO*(1+expπ[h+k+l])+fH*(exp[(π/2)(h+k+l)]+exp[(π/2)(3h+3k+l)]+exp[(π/2)(3h+k+3l)]+exp[(π/2)(h+3k+3l)])

    Here is where I don't know how to keep going; I have never seen something with two different atomic form factors.
    In theory we have seen the case where only the firs term is; in that case, I would say h+k+l=2n+1 so that 1+expπ[h+k+l] becomes zero; but I don't know how to solve this with a second kind of atom.

    Can anyone please help me?

    Thanks for reading.
     
  2. jcsd
  3. Oct 11, 2015 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
     
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