Physics unit 1
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Transcript of Physics unit 1
Crystal Physics
Lattice• Regular , periodical arrangements of points in
three dimension.• Lattice point : The points which presents in the
lattice
Basis
• Group of atom is called as basis
Crystal structure
• Lattice + basis = crystal structure• Crystal structure is obtained by arranging the
basis in each and every lattice point
Unit cell
• Smallest geometric figure , by the repetition of this we get complete crystal structure.
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
Crystal system
CubicOrthorhombicMonoclinicTriclinicHexagonalRhombohedralTetragonal
Bravais lattice
Lattice planes
Miller indices
d spacing in cubic lattice
222 lkh
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Calculation of number of atoms per unit cell – Atomic radius –
Coordination number – Packing factor for SC , BCC ,FCC and HCP
Simple Cubic structure
Atomic radius(r)
• r = a/2
Coordination number (N)
Body Centered Cubic
Number of atoms per unit cell
Coordination number
• For BCC the coordination number is 8
Face Centered Cubic
• Atomic radius = a √2 / 4
HCP
Na Cl structure
ZnS Structure
diamond and graphite Structure
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.
• Allotropes of carbonDiamond and graphite
Crystal defects
• Point defect• line defect • surface defect• Burger vector
Point defect
Line defect
Burger vector
Dislocations
Surface defects
• Grain boundary• Tilt boundary• Twin boundaries• Stacking fault
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