4. Crystal structure
• Lattice + basis = crystal structure
• Crystal structure is obtained by arranging the
basis in each and every lattice point
5. Unit cell
• Smallest geometric figure , by the repetition of
this we get complete crystal structure.
6. Crystal parameters
• The three mutual perpendicular lines OX,OY
and OZ.
• Inter axial lengths: OA = a , OB = b and OC = c
• Inter axial angles: α,β and γ
27. Polymorphism and allotropy
• Polymorphism is a physical phenomenon where
a material may have more than one crystal
structure.
• A material that shows polymorphism exists in
more than one type of space lattice in the solid
state. If the change in structure is reversible,
then the polymorphic change is known as
allotropy.
• The prevailing crystal structure depends on both
the temperature and the external pressure.