x ray crystal structures

amorphous material properties (3)

• broad meltin point

• globular

• no order

crystalline material properties (4)

• narrow melting point

• regular faces and edges

• regular pattern and order

• diffract light

what are the three crystallisation steps

• supersaturation

• formation of nuclei

• crystal growth

why do crystals diffract

because molecules are arranged in an ordered fashion

what happens when an x ray beam strikes a crystal surface at theta

part of the beam is scattered by the layer of atoms at the surface

why do x rays scatter

the electron clouds of the atoms in the crystal

why are x rays scattered in an identical way

as a crystal has atoms in identical position

what is visible light between

400 - 700 nm

how do you calculate constructive interference

using braggs law

what is a unit cell

• smallest repeating internal unit that has the symmetry characteristic of the solid

what are the seven basic crystal systems

• cubic

• tetragonal

• orthorhombic

• rhombohedral

• hexagonal

• monoclinic

• triclinic

cubic unit cells properties

• all sides equal

• all sides equal 90

whats a primitive cubic cell (PC)

atom in each corner of a cube

whats a body centered cube (BCC)

atom in each corner and the centre

whats a face centred cube (FCC)

atom in every corner and on each face

what causes diffraction spots

x rays striking a single crystal