a
a
a
x
y
z
Close packed crystals
A planeB plane
C plane
A plane
…ABCABCABC… packing[Face Centered Cubic (FCC)] …ABABAB… packing[Hexagonal Close Packing (HCP)]
Primitive ( P )
Body Centered ( I )Face Centered ( F )
C-Centered (C )
LATTICE TYPES
p. 13
Example 1: Sodium Chloride (NaCl)radius: Na+ = 1.02nm, Cl- = 1.81nm
radius ratio = 0.563 FCC 4 Cl- packed in FCC, Na+ will fit into the octahedral hole of the anion arrays.
Cl-
Na+
Cl-
Na+
Since stiochiometry of cation and anion = 1:1, 4 Na+ ions fit into the cell. i.e. all the octahedral sites are occupied!
6:6 coordination !
p. 14
Example 2: Zinc Blende (ZnS)radius: Zn2+ = 0.60nm, S2- = 1.84nm
radius ratio = 0.330 FCC 4 S2- packed in FCC, Zn2+ will fit into the tetrahedral hole of the anion arrays.
Since stiochiometry of cation and anion = 1:1, 4 Zn2+ ions fit into the cell. i.e. half the tetrahedral sites are occupied!
S2-
Zn2+
4:4 coordination !
# (Cations fills in the diagonally opposite sites to minimize repulsion.)