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INTERSTICES ANDCRYSTAL DEFECTS

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INTERSTICES AND

CRYSTAL DEFECTS

INTERSTITIAL POSITIONS IN

CRYSTALS

CRYSTALDEFECTS

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INTERSTICES

The presence of large holes in crystalstructure is called interstices.

Interstices in BCC

Interstices in FCC

Interstices in HCP

Comparison of interstices

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INTERSTICES

Interstices in BCCstructure

a) Octahedral site b) Tetrahedral site

Octahedral Tetrahedral

NEXT

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INTERSTICES

Interstices in FCCstructure

a) Octahedral site b) Tetrahedral site

OctahedralTetrahedral

NEXT

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INTERSTICES

Interstices in HCPstructure

a) Octahedral site b) Tetrahedral site

TetrahedralOctahedral

NEXT

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INTERSTICES

Crystal

Structure

Size of

Tetrahed

ral sites

(radius of void

/radius ofhost atom)

Size of

Octahedr

al sites

(radius of void

/radius ofhost atom)

No. of

Tetrahedr

al sites

per unit

cell

No. of

Octahedr

al sites

per unit

cell

BCC 0.291 0.155 12 6

FCC 0.225 0.414 8 4

HCP

(big cell)

0.225 0.414 12 6

NEXT

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POINT DEFECT

LINE DEFECT

SURFACE DEFECT

VOLUME DEFECT

CRYSTAL DEFECTS

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An defect that involves a few atoms

at most at any point in a crystal.

They are also called zero

dimensional defects.

POINTDEFECTS

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TYPES OF POINT DEFECTS

Vacancy (missing of atoms in its

site)

Substitutional (a foreign atom

substitutes a parent atom)

Interstitial ( small sized atomoccupying the void space)

POINTDEFECTS

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Frenkel defect (an ion displaced form a

regular site to an interstitial site in a ionic

crystal without changing charge neutralityof the crystal)

Schottky defect ( a pair of one cation and

one anion with same valency is missing

without changing charge neutrality of the

crystal)

POINTDEFECTS

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POINTDEFECTS

Vacancy

Vacancy

NEXT

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POINTDEFECTS

Substitutional defect

Foreign atom

NEXT

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POINTDEFECTS

NEXTFrenkel defect

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POINTDEFECTS

NEXTSchottky defect

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Line imperfections in a crystal are

called dislocation.

They are one dimensional defects.

LINE DEFECTS

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TYPES OF LINE DEFECTS

Edge dislocation

Screw dislocation

LINE DEFECTS

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EDGE DISLOCATION

Edge Dislocation

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EDGE DISLOCATION

The dislocation where Burger vector ( )

is perpendicular to direction of dislocation

line( ) is called edge dislocation.

{ If we follow a crystallographic plane one

revolution around the dislocation axis,

the vector required to complete the loop

and return us to our starting point is the

burger vector ( ).}

b

t

b

NEXT

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EDGE DISLOCATION

a) Defect free crystal b) Crystal with line defect

Burger vector in edge dislocation NEXT

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SCREW DISLOCATION

Screw Dislocation

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SCREW DISLOCATION

Screw Dislocation

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SCREW DISLOCATION

If the burger vector ( ) and the

dislocation line( ) are parallel then

it is called screw dislocation.

b

t

NEXT

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Two dimensional imperfections are

called Surface defects.

Example: External surface of any

material ( due to breakage of bonds),

Grain boundaries and twinning.

SURFACE DEFECTS

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SURFACE DEFECTS

Grain

Grain boundary

Grain Boundaries NEXT

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VOLUME DEFECTS

Three dimensional imperfections are

called Surface defects.

Example:Cracks , air bubbles, voids

etc.

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CRYSTAL DEFECTS

Dislocation Glide