Post on 22-Jan-2016
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
in (
Co
un
ts)
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10000
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2-Theta - Scale
10 20 30 40 50 60 70 80 90
The diffractogram
Quartz
(Don’t call it spectrum)
Why?
Lin
(Cou
nts)
0
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20000
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2-Theta - Scale
19 20 30 40 50
Identification
PDF = JCPDS
Indexing
Lattice dimensions
Strain
Particle size
Lin
(Cou
nts)
0
1000
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2-Theta - Scale
21 30 40 50 60 70 80
Fluorescens
CuK1 = 1.54056 ÅCuK2 = 1.54433 Å
Primary and secondary monochromators
Rietveld refinement