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Crystall structures of Cu, Al, and Fe at different temperatures.

  1. Oct 3, 2010 #1
    I was wondering if someone could tell me (in pedestrian terms) what are the crystal structures of aluminum, copper and iron as a function of the temperature.
    I just read the chapter on crystalline arrays of Callister's Materials Ecience & Eng. but the book just says that Cu and Al have a FCC structure at room temperature, while Fe has a BCC structure, but it doesn't go much farther than that, and as I have basically no previous knowledge of the subject, I can't easily read more advanced texts.

    Thanks in advance.

    Note. Since this isn't a standard problem-solution type of question I posted it here instead of the homework help sections; please tell me if I should change this.
     
  2. jcsd
  3. Oct 22, 2010 #2
    The phenomenon of a single element having multiple crystal structures is called allotropy. Here's the wikipedia article on the allotropes of iron for example: http://en.wikipedia.org/wiki/Allotropes_of_iron

    If you only want to know what the crystal structures are at various temperature, that's probably information that you can search for. As for the exact reason why an element takes the crystal structure that it does at a given temperature, I'm afraid that that's a complicated condensed matter physics problem, which probably doesn't have any intuitive explanation in most cases. I expect it has to do with the energy distribution of the electrons in the solid at a given temperature, among other things. It probably requires some complicated theoretical modelling.

    It can also depend on the exact conditions in which the material forms, but that's kind of a less fundamental issue.

    Maybe there is a simple physical picture in some of these cases, but I wouldn't hold your breath! Let me know if you find out. :)
     
  4. Nov 17, 2010 #3
    well, there is a concept called polymorphism.including displacive and reconstructive.You can get well understanding if you have a look of the book "Fundamentals of Materials Science"
     
  5. Nov 19, 2010 #4
    normally, Fe will translate from γ-Fe to α-Fe at 912℃. and the former is FCC, while the latter is BCC. The polymorphism will cause the change of coordination number, which will further cause the change of the radii of the atom. Just take Fe for example, the coordination number changes from 12, FCC, to 8, BCC, and the change of the unit volume is about -0.00641
     
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