Amorphous materials
Short range, but no long range order
Similar to the structure of liquids
Example: Glass
Crystalline materials
Atoms or molecules are arranged ina regular pattern with a long range order
crystal lattice
a theoretical construct,a geometric arrayof points in space.
basis
the atoms thatare placed at the lattice points
2D Bravais Lattice
3D Bravais Lattice
Position vector Bravais Lattices in 3D
unit cell
smallest volume elementthat by repetition in 3D describesthe crystal
WIGNER-SEITZ CELL
region of space that is closer to a lattice point than any other
smallest possible primitive cell.
Draw lines from the latticepoint to all others
At the midpoint and normalto these lines, draw new lines(planes in 3D).
Take the smallest polyhedron
MILLER INDICES FOR CUBIC SYSTEMS
Determine the intercept of the plane on the three crystal axes
Take the reciprocals of these intercepts
Convert the reciprocals into the 3 smallest integers
LATTICE SPACING IN CUBIC SYSTEMS - Formular
MILLER INDICES FOR HCP SYSTEMS
Formular Packing fraction
Atoms per unit cell/Volume of unit cell
Packing density formular
mass of atoms in unit cell/Volume of unit cell
BRAGGS LAW - formular
lamda = wave length
Types of STRUCTURAL ANALYSIS TECHNIQUES
X-rays
Electrons
Neutrons
Key points of structural analysis - X-rays
Charge density
weak interaction
not very good for light atoms
use in air
Key points of structural analysis - Electrons
Charge interaction
very strong
only penetrates a few atomiclayers, gives only surface information
need to use in vacuum
Key points of structural analysis - Neutrons
Mainly interacts with mass
Can use with light atoms
Additional magnetic information
Very expensive
Last changed2 years ago