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Materials Moments Rich WVolleyballs Elijah
WCooking surfaces
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Crystallographic Directions and PlanesSolved
Examples posted on Canvas FilesgtSolved
Problems, Assignments, Extra Credit
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Packing and Close-packed Planes
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Close-packed Xl Structures

• FCC HCPAPF .74
• Most efficient packing
• for equal-sized spheres.
• BCCAPF .68
• Not as efficient

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BCC Which is the closest-packed plane?
A)
B)
z
z
D)
C)
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f10_03_pg58
(110) plane packing

• FCCNot a close-packed plane
• BCCclose-packed plane

Figs. 3.11, 3.12
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(110)
(111)
Close-Packed Planes
(0001)
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Different PackingSo What?

• Packing along planes
• Strongly affects deformation
• Atoms can slip past each other on tightly packed
  planes (plastic deformation).

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SEM 100 planes

• SEM single cadmium crystal deforming by
  dislocation slip on 100 planes.

SEM study of slip in deformed cadmium single
crystal
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Sections 3.13-3.15 Single CrystalsPolycrystalli
ne MaterialsAnisotropy
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Terms

• CrystallineRegular repeating order over long
  distances
• Crystal structureshape of atomic arrangement
• Crystal lattice
• Single crystal
• Polycrystalline

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Crystal lattice

• Long-range 3-D representation of a crystal
• Specific location for each atom

Unit Cell
Crystal Lattice
http//chemed.chem.wisc.edu/chempaths/GenChem-Text
book/Lattices-and-Unit-Cells-837.html
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Single Crystals

• Crystal structure repeats perfectly over large
  atomic distance

Galena (Lead ore)
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Polycrystalline materials

• Many small crystals grow together

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Polycrystalline materials

• Extremely small crystals grow together.

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f17_03_pg65
Polycrystalline grain growth
Nucleation sites have random orientations ? xls
have random orientations
Fig. 3.18
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Polycrystalline metal
Micrograph of a polycrystalline metal grain
boundaries evidenced by acid etching.
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AnisotropyProperties dependent
oncrystallographic direction
Isotropy Properties independent of
crystallographic direction.
Polycrystalline copper (SEM)
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Random orientations of anisotropic material
yield isotropic behavior
Polycrystalline Calcite
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Metal Thread Anisotropy
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Section 3.17
Non-Crystalline Solids
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Non-Crystalline Solids

• Amorphouswithout ordered form.
• Formed by rapid cooling from a melt

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Non-crystalline solids
Glass SiO2 (Glassy texture)

• Hand sample of fractured glass
• SEM of fractured glass

www.msm.cam.ac.uk
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f22_03_pg71
Crystalline SiO2
Non-Crystalline SiO2
Fig. 3.23
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Sections 4.1-4.3 Imperfections in Solids
Point defects
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Perfect Crystals
Crystal lattice
Crystal structure
Crystal structure
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Real World of Crystals

• The perfect crystal doesnt exist.
• All materials have defects impurities
• 99.9999 pure metals have
• 1022 1023 impurity atoms/m3

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Crystal defects

• Defectplace where perfect periodicity of unit
  cell is interrupted.

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Dimension Defect Type Examples
0 Point Vacancy, Substitutional
1 Line Dislocations
2 Interfacial Free surface, Grain boundary
3 Volume Pores, cracks, other phases
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Point defects

• I) Intrinsicflaws in xl lattice geometry
  (no impurities)
• II) Extrinsicimpurities

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I. Intrinsic Point Defects 1) Vacancy
STM Germanium (55x70 Å2)
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I. Intrinsic Point Defects 1) Vacancy
An STM image of a self-assembled Au cluster
array. The hexagonal lines illustrate the unit
cell properties of the cluster array. A defect
vacancy is clearly evident. The image was taken
under  ultra-high vacuum conditions. Image by T.
Lee.
Fig. 4.1
http//www.physics.purdue.edu/nanophys/newpage10-0
3/gallery/index.htm
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I. Intrinsic Point Defects 2) Interstitial
Fig. 4.1
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II. Extrinsic Point Defects1) Substitutional
STM Manganese substituted into GaAs (makes
semiconductor magnetic)
Fig 4.2
http//www.mse.engin.umich.edu/research/highlights
/189/the_image_pop
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When can an impurity atom be substitutional?
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Substitutional Atoms

• Atomic radii of host and impurity must be 15

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II. Extrinsic Point Defects2) Interstitial
Fig. 4.2
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When can an impurity atom be interstitial?
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Most common interstitial elements

• Nitrogen
• Oxygen
• Carbon
• Hydrogen

NOCH(e)