Crystal Structures
CH1105: Materials Science
Crystal Structure
Assoc/Prof Timothy Tan Office: N1.2 B2-34 B2Tel: 6316 8829 E-mail: tytan@ntu.edu.sg Semester 1, 2013-2014 2013School of Chemical and Biomedical Engineering
Why study structure of crystalline solids?
To understand how atoms assemble geometrically into solid structures To describe the structure of solids To relate material properties to its structure
2
Energy and Packing
Dense, regular packing Energy typical neighbor bond length typical neighbor bond energy Energy typical neighbor bond length b dl h typical neighbor bond energy Dense, regular-packed structures tend to have lower energy. regular3
r
Non dense, random packing
r
Materials and Packing
Crystalline materials... Atoms pack in periodic, 3D arrays Typical of: - metals - many ceramics - some polymers Long Range Order (LRO)
Noncrystalline materials... Atoms have no periodic packing Occurs for: - complex structures - rapid cooling id li "Amorphous" = Noncrystalline Amorphous"
Short Range Order (SRO)
4
Microscopic Structure
Transmission Electron Microscope (TEM)
TEM image of Si
5
NaCl Crystal Structure
Space filled / hard sphere model of NaCl crystal structure
Lattice model of NaCl crystal structure
6
Space Lattice
Space Lattice A three-dimensional periodic array of points coinciding with the atom three(or spheres) positions. positions. Basis An atom or a group of atoms at each lattice point. point. Crystal structure Lattice + Basis = Crystal structure
7
Unit Cell
Unit cell Smallest repetitive volume which contains the complete lattice pattern of a crystal. Most are parallelepipeds (3D shape with 3 sets of parallel faces). Cell / lattice parameters Edge length a, b, c g g , , Interaxial angles: α (b&c) , β (a&C), γ angles: (a&b) β γ α
8
Crystal Systems and Bravais Lattice
Only 7 different types of unit cells are necessary to create all point lattices. lattices. o Triclinic o
Crystal Structure
Assoc/Prof Timothy Tan Office: N1.2 B2-34 B2Tel: 6316 8829 E-mail: tytan@ntu.edu.sg Semester 1, 2013-2014 2013School of Chemical and Biomedical Engineering
Why study structure of crystalline solids?
To understand how atoms assemble geometrically into solid structures To describe the structure of solids To relate material properties to its structure
2
Energy and Packing
Dense, regular packing Energy typical neighbor bond length typical neighbor bond energy Energy typical neighbor bond length b dl h typical neighbor bond energy Dense, regular-packed structures tend to have lower energy. regular3
r
Non dense, random packing
r
Materials and Packing
Crystalline materials... Atoms pack in periodic, 3D arrays Typical of: - metals - many ceramics - some polymers Long Range Order (LRO)
Noncrystalline materials... Atoms have no periodic packing Occurs for: - complex structures - rapid cooling id li "Amorphous" = Noncrystalline Amorphous"
Short Range Order (SRO)
4
Microscopic Structure
Transmission Electron Microscope (TEM)
TEM image of Si
5
NaCl Crystal Structure
Space filled / hard sphere model of NaCl crystal structure
Lattice model of NaCl crystal structure
6
Space Lattice
Space Lattice A three-dimensional periodic array of points coinciding with the atom three(or spheres) positions. positions. Basis An atom or a group of atoms at each lattice point. point. Crystal structure Lattice + Basis = Crystal structure
7
Unit Cell
Unit cell Smallest repetitive volume which contains the complete lattice pattern of a crystal. Most are parallelepipeds (3D shape with 3 sets of parallel faces). Cell / lattice parameters Edge length a, b, c g g , , Interaxial angles: α (b&c) , β (a&C), γ angles: (a&b) β γ α
8
Crystal Systems and Bravais Lattice
Only 7 different types of unit cells are necessary to create all point lattices. lattices. o Triclinic o