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