test 2

Question 1

NaCl Rock Salt (Halite)

Answer 1

-CCP Cl- with Na+ in all Octahedral holes
-Lattice: fcc
-Motif: Cl at (0,0,0); Na at (1/2,0,0)
-4NaCl in unit cell
-Coordination: (6,6) (octahedral)
-Cation and anion sites are topologically identical

Question 2

CsCl Cesium Chloride

Answer 2

-Motif: Cl at (0,0,0); Cs at (1/2,1/2,1/2)
-1CsCl in unit cell
-Coordination: 8:8 (cubic)
-Adoption by chlorides, bromides and iodides of larger cations,
-e.g. Cs+, Tl+, NH4+

Question 3

ZnS Zinc Blende (Sphalerite)

Answer 3

-CCP S2- with Zn2+ in half Tetrahedral holdes
(only T+ {or T-} filled)
-Lattice: fcc
-4ZnS in unit cell
-Motif: S at (0,0,0); Zn at (1/4,1/4,1/4)
-Coordination: 4:4 (tetrahedral)
-Cation and anion sites are topologically identical

Question 4

CaF2 Fluorite/ {Na2O Anti-Fluorite}

Answer 4

-CCP Ca2+ with F- in all Tetrahedral holes
-Lattice: fcc
-Motif: Ca2+ at (0,0,0); 2F- at (1/4,1/4,1/4) & (3/4,3/4,3/4)
-4CaF2 in unit cell
-Coordination: Ca2+ 8 (cubic) : F- 4 (tetrahedral)
-In the related Anti-Fluorite structure Cation and Anion positions are reversed

Question 5

ZnS Wurtzite (High T Form)

Answer 5

-HCP S2- with Zn2+ in half Tetrahedral holes (only T+ {or T-} filled)
-Lattice: Hexagonal -P
-Motif: 2S at (0,0,0) & (2/3,1/3,1/2); 2Zn at (2/3,1/3,1/8) & (0,0,5/8)
-2ZnS in unit cell
-Coordination: 4:4 (tetrahedral)

Question 6

NiAs Nickel Arsenide

Answer 6

-HCP As with Ni in all Octahedral holes
-Lattice: Hexagonal - P
-Motif: 2Ni at (0,0,0) & (0,0,1/2); 2As at (2/3,1/3,1/4) & (1/3,2/3,3/4)
-2NiAs in unit cell
-Coordination: Ni 6 (octahedral) : As 6 (trigonal prismatic)