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The Crystallography of Nickel Fluoride
Nickel fluoride has the Rutile crystal structure giving it a tetragonal
unit cell. The nickel ions are octahedrally coordinated.
The following image shows a the nickel fluoride unit cell.
In the unit cell the atoms are at the following positions
(Wychoff notation):
|
| Ni: |
(2a) |
0,0,0 ; ½,½,½ |
| F: |
(4f) |
±(uu0 ; u+½,½-u,½) |
Where u=0.302a for NiF2
The following image shows a the nickel fluoride unit cell rotated
to best show the octahedral coordination of the nickel ion.
The Nickel Fluoride Lattice
The arrangement of atoms in the Rutile structure can be difficult
to discern. The following images show clusters and planes in the NiF2
lattice. By looking at these a better appreciation of the geometry
of the lattice can be gained. Note that the lattice has unobstructed "paths"
in certain directions. These can be routes of easy migration of ions in
the lattice. Using Atomistic Simulation, the most favourable migration path
can be predicted.
Nickel Fluoride Lattice Clusters
The following image shows a small cluster of the nickel fluoride
lattice viewed along the [001] direction. Note the clear pathways in the
lattice when viewed from this direction.
The following image shows a small cluster of the nickel fluoride
lattice viewed along the [110] direction.
The following image shows a small cluster of the nickel fluoride
lattice viewed along the [100] direction. Note that absence of clear pathways
in the lattice when viewed from this direction.
Nickel Fluoride Lattice planes
The following image shows the (100) pseudo-plane in NiF2.
Note the pseudo hexagonal close packed fluorine ions. This plane also shows
that the nickel ions occupy one half of the available octahedral sites.
It is this one half occupancy of the octahedral sites that gives rise to
the clear pathways seen above. Interstitial ions can sit in the vacant
octahedral sites.
The following image shows the (001) plane in NiF2.
The following image shows the (110) plane in NiF2.
aCrystal Structures; RWG Wychoff; second edition,
Interscience Publishers
Images created using CASPLOT
(by G.BUSKER)
a utility to visualize the results of CASCADE atomistic simulation calculations.
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