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Question
Explain briefly seven types of unit cells.
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Solution
Seven types of unit cells:
Cubic
a = b = c
α = β = γ = 90°
Rhombohedral
a = b = c
α = β = γ ≠ 90°
Hexagonal
a = b ≠ c
α = β = 90°, γ = 120°
Tetragonal
a = b ≠ c
α = β = γ = 90°
Orthorhombic
a ≠ b ≠ c
α = β = γ = 90°
Monoclinic
a ≠ b ≠ c
α = γ = 90°, β ≠ 90°
Triclinic
a ≠ b ≠ c
α ≠ β ≠ γ ≠ 90°
- Cubic – NaCl
- Rhombohedral – Cinnabar Cubic
- Hexagonal – ZnO
- Tetragonal – TiO2
- Orthorhombic – BaSO4
- Monoclinic – PbCrO4
- Triclinic – H3BO3
They differ in the arrangements of their crystallographic axes and angles.
Corresponding to the above seven, Bravis defined 14 possible crystal systems as shown in the figure.
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