Crystal Structure Ppt1
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Transcript of Crystal Structure Ppt1
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Matter
Solids Liquids Gasses
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Solids are again classified in to two types
Crystalline
Non-Crystalline (Amorphous)
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The materials, which have a regular and periodicalarrangement of atoms or molecules in a solid, are
known as crystalline materials.
Again classified into two typeso Single crystals:
Entire solid consists of only one crystal
o
Poly crystals: It has composed of many small crystals
that are separated by well defined
boundaries.
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Non-Metallic crystals:Ice, Carbon, Diamond, Nacl, Kcl etc
Metallic Crystals:Copper, Silver, Aluminium, Tungsten,Magnesium etc
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Single Crystal example
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Amorphous (Non-crystalline) Solid is
composed of randomly orientated atoms ,
ions, or molecules that do not form defined
patterns or lattice structures.
Amorphous materials have order only within a
few atomic or molecular dimensions.
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Amorphous materials do not have any
long-range order, but they have varying
degrees of short-range order.
Examples to amorphous materialsinclude amorphous silicon, plastics, and
glasses.
Amorphous silicon can be used in solar
cells and thin film transistors.
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Non-crystalline
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The science that studies geometricalform and other physical properties of
crystalline solids called Crystallography
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Lattice
Space lattice
Basis of the crystal structure
Unit cell
Primitive cell
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What is lattice? Lattice is defined as the array of points which are
imaginarily kept to represent the position of atoms in
the crystal.It is an imaginary concept.
What is lattice point? The position of atom or molecules in space denoted by
point is called lattice point or lattice sites
What is lattice lines or directions? The lines joined between the lattice points are called
lattice lines or direction.
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What is lattice planes?
A plane containing lattice points is known aslattice plane or atomic plane
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What is Space lattice ?
An infinite array of pointsin space,
Each point has identical
surroundings to all others.
Arrays are arranged
exactly in a periodic
manner.
a
bCB ED
O A
y
x
That is an infinite three dimensionalarrangement of lattice point in space inwhich the environment about the each
point in same is defined as space lattice
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The arrangement of atoms with lattice
point is called the basisor
A group of atoms which describe
crystal structure
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Crystal structure: When the basis is repeated with
correct periodicity in all directions,we can get the actual crystalstructure.
i.e. Lattice + Basis = Crystal structure
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A unit cell is a smallest unit. Which on
repetition over all the three dimension gives
the actual crystal structure.
A unit cell may be consider as brick of wall.
This unit cell may also known as elementary
pattern or building block or lattice unit.
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S
S
a
S
S
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Lattice parameter or unit cell parameter:
The unit cell and, consequently, the entire lattice, isuniquelydetermined by the six lattice constants: a, b, c,
, and . These six parameters are also called as
basic lattice parameters.
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On the basis of the lengths and directions ofthe axes of the symmetry, all the crystals
may be classified into the following seven
system.
Cubic crystal
Tetragonal crystal
Orthorhombic crystal
Monoclinic crystal Triclinic crystal
Rhombohedral crystal
Hexagonal crystal
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Crystal system Unitvector
Angles
Cubic a= b=c = ==90
Tetragonal a = b c = ==90
Orthorhombic a b c = ==90
Monoclinic a b c ==90 Triclinic a b c 90
Rhombohedral a= b=c = =90
Hexagonal a= b c ==90 =120
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There are 14 possible ways of arranging
points in space lattice from seven crystal
system. These 14 space lattices are known
as Bravais lattices.
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S.No Crystal Type Bravais lattices Symbol
123
Cubic SimpleBody centeredFace centered
PIF
45
Tetragonal SimpleBody centered
PI
6789
Orthorhombic SimpleBase centeredBody centeredFace centered
PCIF
1011
Monoclinic SimpleBase centered
PC
12 Triclinic Simple P
13 Rhombohedral Simple P
14 Hexagonal Simple P
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Number of atoms per unit cell (or) Effective
number Atomic radius
Co-ordination number
Atomic packing factor (or) Packing density(or) density of packing
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The total number of atoms present in orshared by an unit cell is known asnumber of atoms per unit cell.
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Atomic radius is defined as half of thedistance between any two nearest
neighbour atoms which have directcontact with each other
It is usually expressed in terms of cubeedge a.
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Coordination Number (CN) : The number of
nearest neighbouring atoms to a particular atom
in the lattice array.
A simple cubic has coordination number 6; a
body-centered cubic lattice, 8; and a face-
centered cubic lattice,12.
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Atomic Packing Factor (APF) is defined as the
ratio of volume of atoms within the unit cell to
the total volume of the unit cell.
cellunitofVolume
cellunitinatomsofVolume
APF