1. Crystalline Solids (고체의 결정구조)
Associate Professor Su-Jin Kim
School of Mechanical Engineering
Gyeongsang National University

2. OCW 5. Single Crystal, Polycrystalline, Amorphous 11. FCC structure
Families of directions/planes
Crystallographic Points
Crystallographic Directions
Atomic densities and Packing Factors
11. FCC structure
Ionic crystal structures

3. KOCW
결정질 고체의 구조1 결정질 고체의 구조2 결정질 고체의 구조 3

4. Cristal Structure
Atoms (assume hard spheres) are packed BCC, FCC, HCP structures
Atomic Packing Factor, APF (충진율) = Volume of atoms in unit cell / Volume of unit cell
Theoretical density (밀도) = Mass of atoms in unit cell / Volume of unit cell
Crystallographic planes(결정방향) are expressed by Miller indices. ex) (1 0 0)

5. Body Centered Cubic, BCC (체심입방)
Atoms touch each other along cube diagonal corners.
Fe, Cr, W a
√3a R
2 atoms / unit cell

6. Face Centered Cubic, FCC (면심입방)
Atoms touch each other along face diagonals.
Al, Cu, Pb, Ni, Au, Pt, Ag
4 atoms / unit cell
AFP = 0.74

7. Hexagonal Close-Packed, HCP (육방조밀)
Hexagon-Triangle-H-T… Stacking Sequence
Mg, Ti, Zn, Cd
Hexagon
Triangle
6 atoms/unit cell
AFP = 0.74

8. Crystallographic Planes (결정방향)
Miller Indices: Reciprocals of the (three) axial intercepts for a plane. Intercept(교차)Reciprocal(역수)  Integer(정수) values z x y
(110)
(200)
(211)
Intensity (relative)
Diffraction angle 2q
X-ray diffraction pattern (X선회절) for polycrystalline a-iron (BCC)

9. Single crystal, Polycrystalline, Amophous
Amorphous (비정질)
Single crystal diamond
Cast iron grain
Glass

10. Single crystals (단결정)
Material properties generally vary with single crystal orientation. they are anisotropic(이방성).
(111)
Single crystal silicon wafer & anisotropic etching

11. fig_03_18 Polycrystalline (다결정)
Most engineering materials are polycrystalline.
Each grain(결정립) is a single crystal.
If grains are randomly oriented, overall component properties are isotropic(등방성, not directional).
Grain sizes typically range from 1 nm to 2 cm
liquid
crystals grow
polycrystalline
grains
Polycrystalline grains of metal

12. Amorphous (비정질) Amorphous = Noncrystalline
Atoms have no periodic packing
Transparent
ex) Glass Si
Oxygen
noncrystalline SiO2

13. Summary Metallic crystal: FCC, BCC, HCP
Single crystal: Anisotropic (properties vary with crystal orientation)
Poly crystalline: Isotropic (properties are non directional  randomly oriented grains)
Amorphous: Isotropic (random)