MENA3100, 3/2-10, OBK X-ray diffractionXRD Røntgendiffraksjon Single crystalPowder

Diffraction

Crystal Atomic arrangementLattice

1848 The 14 Bravais lattices Lattice + base

Bragg’s law 2d sin  = n

Bragg’s law 2d sin  = n n = 2 But XRD is typically done with monochromatic radiation 2nd. order

Bragg’s law 2d sin  = n 2nd. order from 001 1th. order from 002

The 14 Bravais lattices Face centered cubic lattice  -iron NaCl  -brass

Extinction Example: Face centered cubic Special example: Cubic close packed structure Utslukning

Extinction Example: Face centered cubic Special example: Cubic close packed structure Utslukning

Don’t confuse with...

X-ray diffraction Need X-rays Brehmsstrahlung = white radiation Characteristic X-rays Wavelenght CuK  1 = Å MoK  1 = Å CuK  1 = Å CuK  2 = Å CuK  = Å I(CuK  1 ) = 2·I(CuK  2 )

Need sample Single crystal Powder

Need experimental setup Diffractometer Bragg-Brentano geometry (Primary monochromator) (Secondary monochromator)

Want monochromatic radiation Brehmsstrahlung = white radiation Characteristic X-rays Monochromators: Many possibilities

Euclid, The Elements (300 B.C.) Proposition 21, Book III: The angles in the same segment of a circle are equal to another Johansson monochromator

Bragg-Brentano geometry The source S can be:

Need detector … Need some slits … S Sample Fixed slits: Smaler area at high angle  Smaller area at high angles Variable slits: Same area at all angles

The experiment Got some crystals Want a powder Gets lot of small crystals

Want powder Random orientation

The result The diffractogram Quartz (Don’t call it spectrum)

Why?

Identification PDF = JCPDS

Indexing

Lattice dimensions

Strain Particle size

Fluorescens

CuK  1 = Å CuK  2 = Å Primary and secondary monochromators

Rietveld refinement