Ch03 Notes
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Transcript of Ch03 Notes
8/19/2015
1
CrystalsSpace Lattice and Unit Cells
Seven Different Crystal Systems Overview of Unit Cells
• Cubic Unit Cell a = b = c
α = β = γ = 900
• Tetragonal a =b ≠ c
α = β = γ = 900
Simple Body Centered
Face centered
Simple Body Centered
Figure 3.2
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Types of Unit Cells (Cont..)
• Orthorhombic a ≠ b ≠ c
α = β = γ = 900
• Rhombohedral a =b = c
α = β = γ ≠ 900
Simple Base Centered
Face Centered
Body Centered
Figure 3.2
Simple
Types of Unit Cells (Cont..)
• Hexagonal a = b ≠ c
α = β = 900, γ = 120
• Monoclinic a ≠ b ≠ c
α = γ = 900 , β ≠ 90
• Triclinic a ≠ b ≠ c
α ≠ β ≠ γ ≠ 900
Simple
Simple
Simple
BaseCentered
Figure 3.2
BCC Atomic Packing Factor
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Elements with BCC Hexagonal Close‐Packed Structure
HCP 1st Layer
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Interstitial Spaces Second Layer
HCP 3rd LayerElements with HCP Structure at Room
Temperature
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Face Centered Cubic (FCC) Crystal Structure
Figure 3.6 a&b
FCC
Cubic Closest Packing1st two layers identical to HCP
But now third layer is different(covers remaining holes of first layer)
Only slightly differentHCP and CCP only differ by the C layer. HCP only has two types of layerswhile CCP has three.
A
A
A
B B
C
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Elements with CCP crystal structures at room temp.
Figure 3.10 b
Direction Indicies
(3/4, 0, 1/4)(1/4,1/2,1/2)
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Families Miller Indicies
1/32/3
Distances between planes
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Planes and Directions in Hexagonal Unit Cells
Figure 3.16
Hexagonal Unit Cell ‐ Examples
Directions Volume Density
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Linear Atomic Density Planar Atomic Density
Crystal Structure Analysis
35 KV
X‐Ray Spectrum of Molybdenum
Figure 3.26
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Example spectrumX‐Ray Diffraction
ExamplesInterpret Diffraction Data
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Diffraction Data
BCC Reflecting Planes
This demonstrates simple analysis, actual analysis studiesintensity, width, shape, location