A presentation about crystal structures

1. CRYSTAL
STRUCTURES
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2. WHAT IS A CRYSTAL STRUCTURE …..?
A crystal structure is defined as the particular repeating arrangement of atoms
(molecules or ions) throughout a crystal. Structure refers to the internal
arrangement of particles and not the external appearance of the crystal.
However, these are not entirely independent since the external appearance of a
crystal is often related to the internal arrangement. For example, crystals of
cubic rock salt ( NaCl ) are physically cubic in appearance. Only a few of the
possible crystal structures are of concern with respect to simple inorganic salts
and these will be discussed in detail, however, it is important to understand the
nomenclature of crystallography.
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3. Basic Concepts of Crystal Structure
 Study of Properties of Metals by Structure
Types of Solids
Crystalline Solids
The atoms are positined in systematic pattern.
E.g. Iron, Copper, Aluminum
Non Crystalline Solids
The atoms are positined in nonsystematic pattern.
E.g. Amorphous materials .
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5. SPACE LATTICE :-
A space lattice is an array of points showing
how particles (atoms, ions or molecules) are
arranged at different sites in three dimensional
spaces. Unit cells are easiest to visualize in two
dimensions.
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6. A unit cell is the most basic and least
volume consuming repeating structure
of any solid. It is used to visually
simplify the crystalline patterns solids
arrange themselves in.
UNIT CELL :-
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7. LATTICECONSTANTANDANGLE
 LATTICE CONSTANT
 The lattice constant (or
lattice parameter)
refers to the constant
distance between unit
cells in a crystal
lattice.
 LATTICE ANGLE
lattice parameter is
one of the physical
dimensions
and angles that
determine the
geometry of the unit
cells in a crystal lattice.
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8. CRYSTAL SYSTEMS :-
cubic
System Axial Lengths and Angles Unit Cell Geometry
a=b=c, α = β = γ = 90°
tetragonal a = b ≠ c, α = β = γ= 90°
orthorhombic a ≠ b ≠ c, α = β = γ= 90°
rhombohedral a = b = c, α = β = γ ≠ 90°
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9. System Axial Lengths and Angles Unit Cell Geometry
hexagonal a = b ≠ c, α = β = 90°, γ = 120°
monoclinic
a ≠ b ≠ c, α = γ = 90°, β ≠ 90°
triclinic a ≠ b ≠ c, α ≠ β ≠ γ
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10. TYPES OF CRYSTAL STRUCTURE
1. Simple Cubic Crystal
Structure (SC)
2. Body Centered Crystal
Structure (BCC)
3. Face centered Crystal
Structure (FCC)
4. Hexagonal Closed Packed
Structure (HCP)
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11. Simple Cubic Crystal Structure (SCC)
Ne =No of corner atoms = 8
Nf =No of face atoms =0
Ni =No of interior atoms=0
Navg=Average no of atoms per unit cell
= Nc + Nf+ Ni
8 2 1
8 + 0 + 0
8 2 1
Navg=1
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12. Body centered Crystal Structure (BCC)
Nc= No of corner atoms =8
Nf =No of face atoms =0
Ni =No of interior atoms=1
Navg=Average no of atoms per unit cell
=Nc+Nf+ Ni
8 2 1
8 + 0 + 1
8 2 1
Navg=2
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13. Face centered Crystal Structure (FCC)
Ne =No of corner atoms = 8
Nf =No of face atoms = 6
Ni =No of interior atoms =0
Navg=Average no of atoms per unit cell
=Nc + Nf + Ni
8 2 1
8 + 6 + 0
8 2 1
Navg=4
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14. Hexagonal Closed Packed Structure (HCP)
Nc=No of corner atoms=12
Nf =No of face atoms=2
Ni =No of interior atoms=3
Navg=Average no of atoms per unit cell
=Nc + Nf + Ni
6 2 1
12 + 2 + 3
6 1 2
Navg=6
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15. THANK YOU
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