The document discusses crystal defects and their significance. It begins with an introduction to crystals and crystal defects. There are four main types of crystal defects discussed: point defects, line defects, surface defects, and volume defects. Point defects include vacancies, interstitials, and impurities. Line defects are dislocations like edge and screw dislocations. Surface defects include grain boundaries, twin boundaries, and stacking faults. Volume defects occur on a larger scale and include voids, porosity, and precipitates. In conclusion, the presence discusses how crystal defects can impact properties and significance like improving semiconductor performance or lowering melting points.

1. DEPARTMENT OF PHYSICS
CHUNGNAM NATIONAL UNIVERSITY
DAEJEON
SOUTH KOREA
Presented by:
P. KEDHARESWARA SAIRAM,
PhD Research student,
Presentation on
crystal Defect and its Significance

2.  INTRODUCTION
 CRYSTALS AND CRYSTAL DEFECTS
 TYPE OF CRYSTAL DEFECTS
 SIGNIFICANCE OF CRYSTAL DEFECTS
 CONCLUSION
CRYSTAL DEFECTS

3. INTRODUCTION
 Althoughcrystallinesolids haveshortrangeaswell as long rangeorder in the arrangement of their
constituent particles , yet crystals are not perfect.
 Usuallyasolid consistsof an aggregatesof large noof small crystals.
 Defects have a profound impact on the macroscopic properties of materials.
 Sometimes defects are deliberately created to improve properties of crystal.
CRYSTALS
 A crystal isan organic, inorganic or biological substancewith aspecific chemical comp
osition and definite 3D intermolecularpattern.
 Thestudyof crystals is known ascrystallography.
CRYSTALDEFECTS
 Imperfections in theregulargeometrical arrangementof theatoms in a
crystallinesolid.
The term imperfection or defect is generally used to describe any deviation of the
ideally perfect crystal from the periodic arrangement of its constituents

4. TYPE OF CRYSTAL DEFECTS
1.POINT DEFECTS
2.LINE or LINEAR DEFECTS
3.SURFACE DEFECTS
4.VOLUME DEFECTS

5. POINT DEFECT
If the deviation occurs because of missing atoms, displaced atoms or extra atoms, the
imperfection is named as a point defect.
 CAUSE OF POINT DEFECTS:
Such defects can be the result of imperfect packing during the original crystallisation or they may arise fro
m thermal vibrations of atoms at elevated temperatures because with increase in thermal energy there is
increased probability of individual atoms jumping out of their positions of lowest energy.
TYPE OF POINT DEFECTS
 Pointdefectscan beclassified into 3 types ;
(a)Stoichiometric Defect
(b)Impurity Defects
(c)Non-stoichiometric Defects

6. (A)Stoichiometric Defects
 Thesearethepoint defects thatdon’tdisturb thestoichiometryof thesolid.
 Theyarealsocalled intrinsicorthermodynamicdefects.
 Basically , these are of two types;
(i) Vacancydefects
(ii) Interstitial defects
(i)VACANCY DEFECTS
 When someof the latticesitesarevacant ,thecrystal is said to havevacancydefect. A lattice position that is vacant
because the atom is missing.
 Thisresults in decrease in densityof thesubstance.
 Thisdefectcan alsodevelopwhenasubstance is heated.
 The concentrations of vacancies increase with increasing
temperature and decreasing activation energy.
Vacancy

7.  When someconstituent particles ( atomsor molecules )
occupyan interstitial site, thecrystal is said to have
interstitial defect.
 Thisdefect increases thedensityof thesubstance.
 Vacancyand interstitialdefectsasexplained abovecan be
shown by non
ionicsolids.
 Ionic solid must always maintain electrical neutrality ,
rather than simple vacancyor interstitial defects, and
theseare (iii)Frenkel defect , (iv) Schottky defects
INTERSTITIAL DEFECT
Interstitial
Defect

8. FRENKEL DEFECTS
 If an ion is missing from its correct lattice sites (causing a vaca
ncy or a hole) and occupies an interstitial site, electrical neut
rality as well as stoichiometry of the compounds are maintain
ed
 This type of defect is called Frenkel defect.
 Since cations are usually smaller, it is more common to find
the cations occupying interstitial sites.
This type of defect is present in ionic compounds which have:
i) Low co ordinations number
ii) Larger difference in size of cation and anions
Frenkel Defects

9. SCHOTTKY DEFECT
 If in an ionic crystal of the type A+ B-, equal number of
cations and anions are missing from their lattice. It is
called Schottky defect. Named after Walter. H.Schotty.
 In non-ionic crystals it means a lattice vacancy defect.
In ionic crystals, the defect forms when oppositely charged
ions leave their lattice sites, creating vacancies.
 These vacancies are formed in stoichiometric units, to
maintain an overall
neutral charge in the ionic solid.
This type of defect is shown by highly ionic compounds
which have:
i) High Co – ordination number and
ii) Small difference in the sizes of cations and anions
.

10. (B)IMPURITY DEFECT
 Impuritydefectsarealsocalled extrinsicdefects.
 If molten NaCl containing a littleamountof SrCl2 iscrystallized, someof th
e sites of Na+ ions are occupied by Sr2+ions.
 Each Sr2+ ions replace two Na+ ions.
 Itoccupies thesiteof one ionand othersiteremainsvacant.
 Thecataionicvacancies thus produced areequal in numberto thatof Sr2+
ions.
 Anothersimilarexample is thesolid solution of CdCl2 and AgCl.

11.  If as a result of imperfection, the ratio of number of cation to
anion becomes different from that indicated by the ideal
chemical formula, the defects are called non – stoichiometric
defects.
 These defects arise either due to excess of metal atoms or non
metal atom or presence of impurities / foreign particle.
These are of two types :-
(B.1) metal excessdefects
(B.2) metal deficientdefects
(C) NON – STOICHIOMETRIC DEFECTS

12. • In these defects the positive ions are in excess. These
may arise due to the following two ways :-
• 1. anionic vacancies:
In this case, negative ions may be missing
from their lattice electrical neutrality
• 2. presence of extra cations in interstitial sites:
In this case, there are extra positive ions
occupying interstitial sites and the electrons in another
interstitial sites to maintain electrical neutrality.
(B.2) METAL DEFICIENT DEFECTS(B.1) METAL EXCESS DEFECTS
• These contains less number of positive ions than
negative ions. These arise due to two ways :-
• 1. Cation vacancies : Insome cases,thepositive ions
may be missingfrom theirlattice sites.
• 2. Extra anions occupying interstitial sites:
In this case, the extra anions may be
Occupying interstitial sites position .

13. 2. LINE DEFECTS
Defect that is produced due to the misalignment of atoms
in a crystal lattice.
Line defect produces two types of dislocations;
1) Edge dislocation
2) Screw dislocation.
(I)EDGE DISLOCATION
 It is also called asTaylor-Orowan Dislocation
 Edgedislocationsarecaused bythe termination of a planeof ato
ms in the middle of acrystal
 Theadjacent planesare not straight, but instead bend around theed
geof the terminating plane so that the crystal structure is perfectly
ordered on either side.
 Berger vector is perpendicular to dislocation line.

14. (II) SCREW DISLOCATION
 It is also called as Burger’sDislocation
 It isadefect in which theatomsare notarranged in
a line but theyare in the form of a screw thread w
hich spirals down from one end of the crystal to a
nother in the form of ahelix.
 A screw dislocation can be imagined as being
produced by cutting the crystal partway
through with a knife and then shearing one part of
the crystal with respect to the other parallel to the
cut.
Berger vector is parallel to dislocation line

15. 3.Planar or Surface defects(Two dimensional)
 In planar defect, boundaries or planes are formed, separate the structure
into regions, having the same crystal structure but different orientation.
Planar defects include:
 Grain boundaries
 Twin boundaries
 Tilt boundaries
 Stacking faults
A) Grain Boundaries
 A Grain Boundary is a general planar defect that separates regions of differ
ent crystalline orientation (i.e. grains) within a polycrystalline solid . Grain
boundaries are usually the result of uneven growth when the solid is crystal
lizing.

16. B)Twin Boundaries
 These are the boundaries in the grains at which the
atomic arrangement on one side of the boundary is
the mirror image of the atoms on the other side .T
he volume of material which has an orientation si
milar to the mirror image of the matrix orientation
is called a twin.
C) Tilt Boundaries
 When the angle between two crystals is less than
10 ,the distortion is not so drastic as to be compa
red with a non crystalline material .They are also
called low angle boun-daries.
 It can be described as set of parallel, equa
lly spaced edge dislocation of same sign
located
one above other.
 A Tilt Boundary,
between two slig
htly mis-aligned
grains appearsas
an array of edge
dislocations.

17.  Whenever the stacking of atomic planes is not in a proper sequence throughout the crystal,the
fault caused is known as stacking fault.
 For example, the stacking sequence in an ideal FCC crystal may be described asA-B-C-A-B-
C- A-B-C-……. But the stacking fault may change the sequence to A-B-C-A-B-A-B-A-B-C.
The region in which the stacking fault occurs (A-B-A-B) forms a thin region and it becomes
HCP.
 This thin region is a surface imperfection and is called a stackingfault.
D) Stacking Faults

18. 4. Volume or Volumetric Defects
 Volume defects such as stacking faults may arise when there is only small di
ssimilarity between the stacking sequence of close packed planes in FCC an
d HCP metals.
 The volume defects may affect their mechanical, electrical and optical prop
erties.
 Volumetric defects occur on a much bigger scale than the rest of the
crystal defects. Voids, porosity and precipitates are the volumetric
defects.
 Voids are regions where there are a large number of atoms missing
from the structure. Voids can occur for a number of reasons.
 When voids occur, due to air bubbles which trapped, when a material
solidifies, is commonly called porosity.
 Another type of volumetric defect occurs, when impurity atoms cluster
together to form small regions of a different phase. That is another
form of volumetric defect.
 Volumetric defect due to
porosity

19. SIGNIFICANCE OF CRYSTAL DEFECTS
 The presenceof defectswhich affectthecolourcan make thesecrystals
valuableas Gemsas in Ruby (Crreplacing asmall fractionof theAl in Al2O3)
 Silicon crystals aredoped with Nitrogengroupof elements P and Asor Boron Group
of elements B, Al, etc. to formsemiconductors.
 Presence of impurity leads to the lowering of the melting points
 Screw typedislocationdrives thegrowthof Znic Oxide nanotubeswhich are used in micro-e
lectronics, solar powers, batteriesetc.
 Dislocation in crystals are fundamental to thegrowthand arecharacteristics of all crystallin
e materials.

20. THANKYOU....!