1. Imperfections in Solid Materials
Band theory,
insulators, semiconductors p-and n- type, superconductors

2. “Crystals are like people, it is the defects in them which tend to make them interesting!” - Colin Humphreys.

3. In real materials we find: Crystalline Defects or lattice irregularity
Most real materials have one or more “errors in perfection”
with dimensions on the order of an atomic diameter to many lattice sites
Defects can be classification:
1. according to geometry
(point, line or plane)
2. dimensions of the defect

4. Imperfections in Solids
Solidification- result of casting of molten material
2 steps
Nuclei form
Nuclei grow to form crystals – grain structure
Start with a molten material – all liquid
nuclei
crystals growing
grain structure
liquid
Adapted from Fig.4.14 (b), Callister 7e.
Crystals grow until they meet each other

5. Point Defects Vacancy self- interstitial • Vacancies:
-vacant atomic sites in a structure.
Vacancy
distortion
of planes
• Self-Interstitials:
-"extra" atoms positioned between atomic sites.
self-
interstitial
distortion
of planes

6. Point Defects in Alloys
Two outcomes if impurity (B) added to host (A):
• Solid solution of B in A (i.e., random dist. of point defects) OR
Substitutional solid soln.
(e.g., Cu in Ni)
Interstitial solid soln.
(e.g., C in Fe)
• Solid solution of B in A plus particles of a new
phase (usually for a larger amount of B)
Second phase particle
--different composition
--often different structure.

7. Line Defects Are called Dislocations: Schematic of Zinc (HCP): And:
• slip between crystal planes result when dislocations move,
• this motion produces permanent (plastic) deformation.
Schematic of Zinc (HCP):
• before deformation
• after tensile elongation
slip steps which are the physical evidence of large numbers of dislocations slipping along the close packed plane {0001}
Adapted from Fig. 7.8, Callister 7e.

8. Edge Dislocation
Edge Dislocation
Fig. 4.3, Callister 7e.

9. Motion of Edge Dislocation
• Dislocation motion requires the successive bumping
of a half plane of atoms (from left to right here).
• Bonds across the slipping planes are broken and
remade in succession.
Atomic view of edge
dislocation motion from
left to right as a crystal
is sheared.
(Courtesy P.M. Anderson)

10. Screw Dislocations b Dislocation line (b) Burgers vector b (a)
Adapted from Fig. 4.4, Callister 7e.

11. Edge, Screw, and Mixed Dislocations
Adapted from Fig. 4.5, Callister 7e.

12. Imperfections in Solids
Dislocations are visible in (T) electron micrographs
Adapted from Fig. 4.6, Callister 7e.

13. MICROSCOPIC EXAMINATION
Applications
To Examine the structural elements and defects that influence the properties of materials.
Ensure that the associations between the properties and structure (and defects) are properly understood.
Predict the properties of materials once these relationships have been established.
Structural elements exist in ‘macroscopic’ and ‘microscopic’ dimensions

14. Optical Microscopy • Useful up to 2000X magnification (?).
• Polishing removes surface features (e.g., scratches)
• Etching changes reflectance, depending on crystal orientation since different Xtal planes have different reactivity.
0.75mm
crystallographic planes
Adapted from Fig. 4.13(b) and (c), Callister 7e. (Fig. 4.13(c) is courtesy
of J.E. Burke, General Electric Co.
Micrograph of
brass (a Cu-Zn alloy)

15. Band Theory of Solids
A useful way to visualize the difference between conductors,insulators and semiconductors is to plot the available energies for electrons in the materials.

16. Electrical Conductivity in Diamond
sp3 hybridization
localized s orbitals
insulator

17. Conductor, Semiconductor, and Insulator

18. Doped Semiconductors
n-type
p-type

19. Chemistry In Action: High-Temperature Superconductors

23. Crystal structure determination

25. C6H6O3S