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Symmetry in crystal structures- please help

  1. Oct 10, 2004 #1
    Symmetry in crystal structures- please help!!!

    Hi there, I was hoping someone here could help explain a few things about crystal symmetry to me cos it hs me so confused (we've been doing crystals for 2 weeks and things up til now have been ok, I'm just getting myself muddled as usual!). The attachment is of the diagram handed out with our assignment this week and for one of the questions we've to spot mirror planes, glies planes, screw axes and centres of symmetry.

    All I've come up with so far has been 2 mirror planes marked in red, 2 screw diads marked in red splodges, 2 diagonal glide planes marked in blue (with translation in the plane of the paper), a centre of symmetry marked in purple and 3 glide planes marked in green (translation both perpenciular and parallel to the plane of the page). I'm really unsure about my glide planes though because can they just go straight through the atoms like that (I'm talking about the ones marked in blue).? The ones we've covered in lectures have always ran between 2 sets of atoms, not up the middle of some of them (like can you not have this because it'd be like cutting the atom in half and translating it?!). Also, have I got my centre of symmetry right? Could someone maybe give me a good description of what it actually is? We have a definition of it with inversion in it, but I don't really get inversion (yet another thing that would be great if someone could explain).

    If anyone could give me a hand at all with this or let me know where I'm going wrong etc, I'd be really grateful. At the moment all I seem to be doing is reading about crystals and actually having someone to sort out a few of the bits and pieces I'm stuck on would be fantastic. Thanks.

    Claire :eek:
     

    Attached Files:

  2. jcsd
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