1. CRYSTAL IMPERFECTIONS

2. Outline
1. Introduction
2. Classification of imperfections
3. Effects of imperfections on properties

3. Introduction
• The "right" atoms in "wrong" places.
• "Wrong" atoms in "right" or "wrong" places.
• Missing atoms.

4. Crystal
Defects
Volume Defects
Surface Defects
Line Defects
Point Defects

5. POINT DEFECTS

6. Substitutional impurity
Point Defects
Vacancy
Substitutional impurity
Self-Interstitials
Interstitial Impurity
Frenkel imperfection
Schottky imperfection

7. Vacancy:
Tensile Stress Fields ?

8. vacant atomic sites in a structure
Vacancy
distortion
of planes

9. Substitutional Impurity:
Compressive stress fields
Tensile Stress Fields

10. Point Defects in Metals
Self-Interstitials:
Self-interstitial
distortion of planes

11. Interstitial Impurity
Relative size
Compressive Stress Fields

12. Frenkel imperfection
vacancy + interstitial site

13. Schottky imperfection

14. Electronic Defects

15. Frenkel and Schottky defects

16. Line Defects
Edge Dislocation
Screw Dislocation

18. Burger Vector

19. Screw Dislocation
Slip Planes
Screw
Dislocation
Slip Direction

22. Screw Dislocation

23. Surface Defects or
Interfacial defects

24. Surface or Interfacial Defects
External Surface
Grain boundaries
Tilt boundary
Twist boundary
Twin boundary
Stacking defects

25. External Surface

26. Grain Boundaries (or) Crystal Boundary

27. Tilt Boundaries

28. Twin Boundaries

29. Stacking Defect

30. Volume Defects Crakes Pores Voids
Affects mechanical, electrical and optical properties.

31. Effect of crystal imperfections and their applications:
They change mechanical, electrical, magnetic and optical properties of a material.
Materials undergo elastic/plastic deformation. The deformation occurs due to the movement of dislocations.
Any other defect in crystal disrupts the motion of dislocation. It makes plastic deformation more difficult.
Fatigue: Weakening of material, when it is subjected to stress repeatedly.