Crystal structure wurtzite

  1. As far as I understand wurtzite is the name given to the crystal structure defined by the stacking sequence ABABABAB..
    However, I am having a hard time understanding what the unit cell is of wurtzite. From what I know the unit cell is the smallest repetitive unit and in it you specify the position of the different atoms. So I looked up something about wurtzite and found that data:
    http://som.web.cmu.edu/structures/S014-ZnO.html
    And according to this you only need to specify the position of two atoms, while the unit cells seems to encapsulate a lot more atoms - why are the positions of these not specified?
    And another question: The meaning of the coordinates (x,y,z) is x*a1,y*a2,z*a3, where a1,a2,a3 are the unit vectors of the hexagonal lattice - right?
    Thanks for taking your time
     
  2. jcsd
  3. The answer is easy. Two atoms do not form a cell but what is called an asymmetric unit: http://en.wikipedia.org/wiki/Crystal_structure#Unit_cell
    The unit cell is obtained from the asymmetric unit by applying symmetrical operations.
     
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