Material Science and Engineering, Imperfections in Solids, Types, Description and Short Quiz

1. IMPERFECTIONS
IN SOLIDS
REPORTERS:
MARK STEPHEN P. MADRONIO
BSEE 4C

2. OBJECTIVES:
● Understand each kind of imperfections in solids.
● Identify the imperfections base on description
and examples.
● Differentiate the imperfections of solids to each
other.

3. What are the Imperfections in Solids?
● Any deviation from completely ordered
arrangement of constituent particles in a crystal
is called disorder or a defect.
● Any abnormality in the pattern of crystal
arrangement in solids

4. TYPES OF IMPERFECTIONS OR DEFECTS
POINT DEFECTS
- The defects which arise due to the irregularity or deviations from ideal
arrangement of atoms around a point or point or an atom in a crystalline
substance are called point defects or atomic imperfections.
LINE DEFECTS
- The defects which arise due to irregularities or deviations from ideal
arrangement in entire row of of lattice point are called line defects.
These irregularities are called crystal defects or crystal imperfections.

5. POINT DEFECTS

6. LINE DEFECTS

7. POINT DEFECTS
● Vacancy defect
● Interstitial defect
○ Defects in stoichiometric crystals.
○ Defects in non stoichiometric crystals.
○ Impurity defects.

8. ● When some of the lattice sites are vacant, the crystal is said
to have vacancy defect.
Vacancy Defects

9. ● When some constituent particles (atoms or molecules) occupy
vacant interstitial positions, the crystal is said to have
interstitial defects.
Interstitial Defects

10. ● Stoichiometric compounds
- are those in which the number of positive and negative
ions are exactly in the ratios indicated by their chemical
formulae.
There are two types
● Schottky Defect
● Frenkel Defect
Defects in Stoichiometric Crystals

11. ● A Schottky defect is an excitation of the site occupations in a
crystal lattice leading to point defects named after Walter H.
Schottky.
● In ionic crystals, this defect forms when oppositely charged
ions leave their lattice sites and become incorporated for
instance at the surface, creating oppositely charged
vacancies.
Conditions causing Schottky Defects
● High coordination number.
● Ions of almost similar size.
Schottky Defect

12. Schottky Defect

13. ● A Frenkel defect is another form of a point defect which is
created when an atom or cation leaves its original place in the
lattice structure to create a vacancy while occupying another
interstitial position within the solid crystal.
Condition causing Frenkel Defects
● Low coordination number.
● Anions are much larger in size than the cations.
Frenkel Defect

14. Frenkel Defect

15. ● Non-Stoichiometric Defects
The compound in which the ratio of positive and
negative ions present in the compound differs from that
required by ideal chemical formula of the compound are
called non-stoichiometric defects.
These are of two types
● Metal Excess Defects
● Metal Deficiency Defects
Defects in Non-Stoichiometric Crystals

16. Metal Excess Defects
● Metal excess defect is a type of point defect that is capable of
disturbing the stoichiometry of an ionic solid.
● The perfect crystalline structure undergoes a non-
stoichiometric distortion due to the absence of anions at specific
positions or addition of extra cations.
These may arise due to the following ways
● Anionic vacancies
● Presence of extra cations in interstitial sites

17. Metal Excess Defects

18. Metal Excess Defects
● Anion Vacancies
○ In this case, negative ions may be missing from their lattice
electrical neutrality

19. Metal Excess Defects
● 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.

20. ● Metal deficiency defect is a crustal defect caused due to the
absence of anions or presence of excess cations at interstitial
sites.
● Metal Deficiency defect is a kind of disorder that occurs in
compounds wherein the metal can show off variable valency.
For example- Transition metallic compounds.
These arise due to two ways
● Cation vacancies
● Extra anions occupying interstitial sites
Metal Deficiency Defects

21. Metal Deficiency Defects

22. Metal Deficiency Defects
● Cation Vacancies
○ In some cases, the positive ions may be missing from their
lattice sites.

23. Metal Deficiency Defects
● Extra Anions Occupying Interstitial Sites
○ In this case, the extra anions may be occupying interstitial
sites position .

24. ● Impurity defect is defined as the foreign atoms that
compress into the interstices or replace some atoms that
make up the solid.
● The defects in ionic compounds due to replacing ions by
ions of another compound are called impurity defects.
Impurity Defects

25. Impurity Defects

26. LINE DEFECTS
● Line defects are called dislocations and occur in crystalline
materials only.
● Dislocations are especially important in materials science,
because they help determine the mechanical strength of
materials.
There are two basic types of dislocations
● Edge dislocation
● Screw dislocation

27. LINE DEFECTS
● Mixed dislocations, combining aspects of both types, are
also common.
● It is important to note that dislocations cannot end inside a
crystal. They must end at a crystal edge or other dislocation,
or they must close back on themselves.
● During the 1930s it was theorized that this discrepancy in
mechanical strengths could be explained by a type of linear
crystalline defect that has come to be known as a
dislocation.
● The term ‘dislocation’ referring to a defect on the atomic
scale was coined by G. I. Taylor in 1934.

28. LINE DEFECTS

29. Edge Dislocation
● Edge dislocation centers around the edge dislocation line that is
defined along the end of the extra half-plane of atoms.
● The imperfection may extend in a straight line all the way
through the crystal or it may follow an irregular path.
● It may also be short, extending only a small distance into the
crystal causing a slip of one atomic distance along the glide
plane (direction the edge imperfection is moving).

30. Edge Dislocation
● Macroscopic plastic deformation simply corresponds to
permanent deformation that results from the movement of
dislocations, or slip, in response to an applied shear stress.
● Dislocations can move if the atoms from one of the surrounding
planes break their bonds and rebond with the atoms at the
terminating edge.

31. Edge Dislocation

32. Screw Dislocation
● Screw dislocations can be produced by a tearing of the crystal
parallel to the slip direction.
● If a screw dislocation is followed all the way around a complete
circuit, it would show a slip pattern similar to that of a screw
thread.
● A screw dislocation is much harder to visualize. Imagine cutting a
crystal along a plane and slipping one half across the other by a
lattice vector, the halves fitting back together without leaving a
defect.

33. Screw Dislocation
● The motion of a screw dislocation is also a result of shear stress,
but the defect line movement is perpendicular to direction of the
stress and the atom displacement, rather than parallel.
● The pattern may be either left or right handed. This requires that
some of the atomic bonds are re-formed continuously so that the
crystal has almost the same form after yielding that it had before.

34. Screw Dislocation

35. QUIZ:
1. Any abnormality in the pattern of crystal arrangement.
2. The abnormality that arise due to irregularity from ideal arrangement of an atoms around a point.
3. The abnormality that arise due to irregularity from ideal arrangement in an entire row of lattice points.
4-5. What are the two types of point defects.
6. This defect is an excitation of the site occupations in crystal lattice leading to point defects.
7. A point defect which is created when an atom or cation leaves its original place in the latice structure to
create a vacancy while occupying another interstitial position within the solid crystal.
8-9. Two types of Non-Stoichiometric Crystals.
10. Give one of the types of Line Defect.
11-12. Identify two kinds of imperfections in the figure shown. Write the corresponding letter and your
answer.

36. PLEASE IDENTIFY:
A B C
D E

37. REFERENCES:
Crystal Defects:Point Defects. Vedantu. Retrieved September 7, 2022 from
https://www.vedantu.com/chemistry/point-defects-in-crystals
Crystal Line Defect. Science Direct. Retrieved September 7, 2022 from
https://www.sciencedirect.com/topics/chemistry/crystal-line-defect
Imperfection in Solids. GeeksForGeeks. Retrieved September 7, 2022 from
https://www.geeksforgeeks.org/imperfection-in-
solids/#:~:text=Imperfections%20or%20Defects%20in%20a%20Solid&text=Any%20deviation%20from%20the%20pe
rfectly,of%20crystal%20arrangement%20in%20solids
Point Defects. Byjus. Retrieved September 7, 2022 from https://byjus.com/chemistry/imperfections-in-solids-point-
defects/
Point Defect. Science Direct. Retrieved September 7, 2022 from https://www.sciencedirect.com/topics/materials-
science/point-defect
What are Line Defects – Dislocations – Definition. Material Properties. Retrieved September 7, 2022 from
https://material-properties.org/what-are-line-defects-dislocations-definition/

38. THANK YOU!