Interstices in the BCC structure
Tetrahedral interstices
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Press Cell->Remove and click the mouse over the cell, to remove it.
Otherwise, just scale it down and move it away from the center, to economize
space. This way, the two cells containing octahedral and tetrahedral
interstices can be compared later.
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Press Cell->Create and set System to c,
Lattice to I (Body-Centered Cubic) and a
to 2.309 (so the structural atoms will be in contact
along <111> directions). Press Ok to create the cell.
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Press Atom->Modify and click the mouse over the interstitial
atom, to select it. Change its Radius to 0.291, the size
of the BCC tetrahedral interstices and press Ok.
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Press Cell->Link and select the Crystal link method.
Press the mouse over the cell, and then over the interstitial atom,
to identify the objects to link. Set x, y, z
coordinates (Position page) to 0.0, 0.25,
0.5 and press Ok. 4 interstitial atoms are now visible,
corresponding to 2 interstices inside the cell or 1/6 of the tetrahedral
interstices available.
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Repeat the procedure above with x, y, z coordinates set
to 1) 0.0, 0.5, 0.25; 2) 0.25, 0.0, 0.5;
3) 0.5, 0.0, 0.25; 4) 0.25, 0.5, 0.0 and
5) 0.5, 0.25, 0.0 to allocate the remaining interstices.
24 interstitial atoms are now visible, 4 per face, corresponding to a total
of 12 tetrahedral interstices inside the cell.
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To represent the structural atoms, repeat the link procedure above,
but this time pressing the mouse over the Fe structural atom, to identify
the linked atom, and setting x, y, z coordinates
to 0.0, 0.0, 0.0. 9 structural atoms are now visble,
8 in the vertices and 1 in the center, corresponding to a total of 2 atoms
inside the cell.
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To remove the Fe,C atoms used as models during the building process,
press Atom->Remove and click the mouse over them.
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Rotate,move,scale the cell with the mouse. To have a better view inside
the cell, remove some of the structural atoms outside. Select
Atom->Remove and press the mouse over the atoms to remove.