MENA3100, 3/2-10, OBK

X-ray diffraction XRD

Røntgendiffraksjon

Single crystal Powder

Diffraction

Crystal

Atomic arrangement Lattice

1848The 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

CuK1 = 1.54056 ÅMoK1 = 0.70930 Å

CuK1 = 1.54056 ÅCuK2 = 1.54433 Å

CuK = 1.5418 Å

I(CuK1) = 2·I(CuK2)

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 resultL

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2-Theta - Scale

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The diffractogram

Quartz

(Don’t call it spectrum)

Why?

Lin

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2-Theta - Scale

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Identification

PDF = JCPDS

Indexing

Lattice dimensions

Strain

Particle size

Lin

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nts)

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Fluorescens

CuK1 = 1.54056 ÅCuK2 = 1.54433 Å

Primary and secondary monochromators

Rietveld refinement