X Ray crystallography

1. 1
X RAY CRYSTALLOGRAPHY
Presented by:
Tathagata Pradhan
M.Pharm (Chemistry)

2. INTRODUCTION
• X-ray crystallography (XRC) is the experimental
science determining the atomic and molecular structure
of a crystal, in which the crystalline structure causes a
beam of incident X-rays to diffract into many specific
directions. By measuring the angles and intensities of
these diffracted beams, we can produce a three-
dimensional picture of the density of electrons within
the crystal. From this electron density, the mean
positions of the atoms in the crystal can be determined,
as well as their chemical bonds, their crystallographic
disorder, and various other information.
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3. HISTORY
• X-rays were discovered by WC Rontgen in 1895
• In 1912, PP Ewald developed a formula to describe the
passage of light waves through an ordered array of
scattering atoms, based on the hypothesis that crystals
were composed of a space-lattice-like construction of
particles.
• Maxwell Von Laue realized that X-rays might be the
correct wavelength to diffract from the proposed space
lattice.
• In June 1912, Von Laue published the first diffraction
pattern in Proceedings of the Royal Bavarian Academy
of Science.
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4. ELECTROMAGNETIC SPECTRUM
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5. DIFFRACTION BASICS
DIFFRACTION:-Diffraction is the slight bending of
light as it passes around the edge of an object.
Conditions for diffraction
• For electromagnetic radiation to be diffracted the
spacing in the grating should be of the same order as
the wavelength
• In crystals the typical interatomic spacing is 2-3 Å so
the suitable radiation is X-rays 0.1-10 Å (more
energetic can penetrate deep into the material)
• Hence, X-rays can be used for the study of crystal
structures.
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7. BRAGG’S EQUATION
• It states that when a beam of X-rays of
wavelength λ enters a crystal, the maximum
intensity of the reflected ray occurs when
sin θ = nλ/2d, where θ is the angle of
incidence, n is a whole number, and d is the
distance between layers of atoms.
BRAGG’S EQUATION:-
sin θ = nλ/2d
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8. BRAGG’S LAW
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9. INSTRUMENTATION
 X RAY SOURCE
1. Crooke’s Tube
2. Coolidge’s Tube
 COLLIMATORS
 MONOCHROMATORS
1. Filter type
2. Crystal type
 DETECTORS
1. Photographic Methods
2. Counter Methods
a) Geiger Muller Counter
b) Proportional Counter
c) Scintillation Counter
d) Solid State Semiconductor Detector
e) Semiconductor Detector
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10. INSTRUMENTATION
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11. PRODUCTION AND PROPERTIES OF X
RAYS
• X Rays are produced by acceleration of high
energy electrons or electronic transitions of
electrons in the inner orbitals of atoms.
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12. I. X RAY SOURCE
1. CROOKE’S TUBE:-
• Also known as cold
Cathode tube.
• Early experimental electrical discharge tube,
with partial vacuum,
• Electrons are generated by ionization of
residual air in the tube, instead of heated
filament.
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13. • An aluminium cathode
Plate at one end of the tube
Created a beam of electrons,
Which struck a platinum
Anode target at the center generating X rays
ADVANTAGE:-
Point Source:-X Rays which resulted in sharper
images
Disadvantage:-unreliable and temperamental.
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14. 2. COOLIDGE’S TUBE
• Spherical glass bulb with cylindrical stems
carrying the electrodes.
• The Coolidge Tube, first produced in 1913 by
W. Coolidge
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15. WORKING OF COOLIDGE’S TUBE
• A tungsten filament is used as the tube cathode,
and during operation is heated to incandescence
by passing a current through it. This causes the
filament to emit electrons at a rate dependent on
the temperature of the filament. The electrons are
then accelerated towards the tube anode by the
strong tube voltage. Upon hitting the anode, the
electrons are decelerated very rapidly, and shed
their excess kinetic energy mostly as heat, and
partly as x-ray radiation.
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16. Collimators
• Collimator is a device that narrows a beam of
particles or waves. Narrow means to cause the
directions of motion to become more aligned
in a specific direction. It is achieved by using a
series of closely spaced, parallel metal plates r
by a bundle of tubes, 0.5 or less in diameter.
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17. MONOCHROMATORS
• The device used to select radiation of (or very
close to) a single wavelength or energy.
OR
• A monochromator is an optical device that
transmits a mechanically selectable narrow band
of wavelengths of light or other radiation chosen
from a wider range of wavelengths
• TYPES:- 1. FILTER TYPE
2. CRYSTAL TYPE
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18. MONOCHROMATORS
1. FILTER
A filter is a window of material
that absorbs undesirable
radiation but allows the
radiation of required
wavelength to pass. e.g..
Zirconium filter which is used
for molybdenum radiation.
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19. MONOCHROMATORS
2. Crystal monochromator
• It is made up of a suitable
crystalline material
positioned in the x ray beam
so that angle of reflecting
planes satisfied the Bragg's
equation for required
wavelength. e.g. flat crystal
monochromator
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20. DETECTORS
• It is a device which is used to convert light energy into
electrical energy.
1. PHOTOGRAPHIC METHODS
• X-ray film contains silver halide crystal "grains“
• When the film is exposed to radiation the halide
is ionised and free electrons are trapped in crystal
defects (forming a latent image). Silver ions are attracted to
these defects and reduced, creating clusters
of transparent silver atoms. In the developing process these
are converted to opaque silver atoms which form the
viewable image, darkest where the most radiation was
detected.
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21. 21

22. 2. COUNTER METHODS
A) GEIGER MULLER
COUNTER
• Filled with an inert gas
like argon
• Measures ionizing
radiation. Detect the
emission of nuclear
radiation: alpha
particles, beta particles
or gamma rays.
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23. DIAGRAM OF GEIGER MULLER
COUNTER
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24. WORKING OF GEIGER MULLER
COUNTER
• The Geiger–Müller tube is filled with an inert gas
such as helium, neon, or argon at low pressure, to
which a high voltage is applied. The tube briefly
conducts electrical charge when
a particle or photon of incident radiation makes
the gas conductive by ionization. The ionization is
considerably amplified within the tube by
the Townsend discharge effect to produce an
easily measured detection pulse, which is fed to
the processing and display electronics.
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25. GEIGER MULLER COUNTER
Advantages:
a)Trouble free
b)Inexpensive
Disadvantages:
a) Cannot be used to measure energy of ionizing radiation.
b)Used for low counting rates.
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26. B) Proportional counter
• Filled with heavier gas
like xenon or krypton
as it is easily ionized.
• Output pulse is
dependent on
intensity of X-rays
falling on counter.
• Count the particles of
ionizing radiation and
measures their
energy.
H
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27. B) Proportional counter
• Advantages:
• a)Count high rates with out significant
error.
• Disadvantages:
• a)Associated electronic circuit is complex.
• b)Expensive.
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28. C) SCINTILLATION COUNTER
• A scintillation counter is an instrument for detecting
and measuring ionizing radiation by using the
excitation effect of incident radiation on a scintillating
material, and detecting the resultant light pulses.
• The sensor, called a scintillator, consists of a
transparent crystal, usually phosphor, plastic (usually
containing anthracene), or organic liquid that fluoresces
when struck by ionizing radiation.
• The PMT is attached to an electronic amplifier to count
and possibly quantify the amplitude of the signals.
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29. WORKING OF SCINTILLATION
DETECTOR
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30. D) Solid state semi-conductor
detector
The electrons produced by X-ray beam are
promoted into conduction bands and the
current which flows is directly proportional to
the incident X-ray energy.
Disadvantage:
Maintainted at very low Temp to minimise the
noise and prevent deterioration of the
detector.
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31. E) Semi-conductor detectors
• Silicon-lithium drifted detector.
• The principle is similar to gas ionization
detector.
• Voltage of pulse=Q/C
Application:
• In neutron activation analysis.
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32. X-RAY DIFFRACTION METHODS
1.Laue photography method
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The Laue method is mainly used to determine the orientation of large single
crystals. White radiation is reflected from, or transmitted through, a fixed
crystal.
Back-reflection Laue
In the back-reflection
method, the film is Placed
between X-ray source and
crystal.
The beams which are diffracted
in a backward direction are
recorded.
 Transmission Laue
The film is
placed behind the crystal to
record beams which are
transmitted through the crystal.
Disadvantage: Big crystals are required

33. 1
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Back-reflection Laue Back-reflection Laue
Crystal orientation and perfection is determined from the position
of spots.

34. BACK REFLECTION LAUE
 Used to determine crystal orientation
 The beam is illuminated with ‘white’ radiation
 Use filters to remove the characteristic radiation wavelengths
from the X-ray source
 The Bremmsstrahlung radiation is left
 Weak radiation spread over a range of wavelengths
 The single crystal sample diffracts according to
• Bragg’s Law
 Instead of scanning the angle theta to make multiple
crystallographic planes diffract, we are effectively ‘scanning’ the
wavelength
 Different planes diffract different wavelengths in the X-ray
beam, producing a series of diffraction spots
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35. 2.BRAGG X-RAY SPECTROMETER
METHOD
• Bragg analysed the structures
of NaCl, KCl and ZnS.
• Method is based on Bragg’s
law.
• The strength of ionisation
current is directly proportional
to intensity of entering
reflected X-rays.
• SO2 or CH3I increases
ionisation in the chamber.
q
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36. 3.ROTATING CRYSTAL METHOD
• Shaft is moved to put the
crystal into slow rotation.
• This cause sets of planes
coming successively into their
reflecting position.
• Each plane will produce a spot
on the photographic plate.
• Can take a photograph of the
diffraction pattern in two ways
• 1.complete rotation method
2.oscillation method
• q
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37. 4.POWDER CRYSTAL METHOD
• q • q
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38. If a powdered crystal is used instead of a single
crystal, then there is no need to rotate it, because
there will always be some small crystals at an
orientation for which diffraction is permitted.
Here a monochromatic X-ray beam is incident
on a powdered or polycrystalline sample. Useful
for samples that are difficult to obtain in single
crystal form. The powder method is used to
determine the lattice parameters accurately.
Lattice parameters are the magnitudes of the
primitive vectors a, b and c which define the unit
cell for the crystal.
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39. • 1mg material is sufficient for study.
Applications: useful for
• Cubic crystals.
• Determining complex structures of metals
and alloys.
• Making distinction between allotropic
modification of the same substance
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40. Applications of XRD
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• Determination of the structure of the crystals.
The analytical applications of X-ray diffraction
are numerous. The method is non-destructive and
gives information on the molecular structure of
the sample. Perhaps its most important use has
been to measure the size of crystal planes. The
patterns obtained are characteristic of the
particulars compounds from which the crystal
was formed.

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Example:
NaCl and KCl give different diffraction patterns.
A mixture containing 1% KCl in NaCl would show a
diffraction pattern of NaCl with a weak pattern of KCl.
On other hand, a mixture containing 1% NaCl in KCl
would show the diffraction pattern of KCl with a weak
pattern of NaCl.

42. Difference between mixture of crystal
and mixed crystal
The crystal of sodium potassium chloride(mixed
crystal) would changes the crystal lattice size , when
there is a large excess of sodium over potassium , the
pattern would be similar to that of sodium chloride.
However as potassium increases, the lattice
dimension changes accordingly they equal that of
potassium chloride . On the other side, similar pattern
will occur in case of excess of potassium occur over
sodium, which would give diffraction of potassium
chloride
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43. • Polymers characterisation.
Powder method can be used to determine the
degree of crystalline of the polymer. The non-
crystalline portion simply scatters the X-ray
beam to give a continuous background, while the
crystalline portion causes diffraction lines that
are not continuous.
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44. • Determination of the orientation of the
crystalline structure.
By the help of rotating crystal method, the
different orientation of crystals can be determined.
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XRD pattern of NaCl powder

45. • Analysis of chemical composition of milk
stone.
X-ray diffraction technique has also been applied
for analysing the chemical composition of milk
stones. Since each chemical compound gives a
definite pattern on a photographic film according
to atomic arrangement, X-rays can be used for
qualitative chemical analysis as well as structural
analysis.
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46. • Identification of the impurity
If any impurity is present in a sample, the
additional lines will be present in x ray spectrum,
which can be identified by comparing x ray
diffraction computer memory bank.
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47. State of anneal in metals
• A property of metals than can be determined
by X-ray diffraction is the state of anneal. •
Well-annealed metals are in well-ordered
crystal form and give sharp diffraction lines. •
If the metal is subjected to drilling,
hammering, or bending, it becomes fatigued,"
that is, its crystals become broken and the X-
ray pattern more diffuse.
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48. Miscellaneous Application
• Soil classification based on crystallinity
• Corrosion products can be studied by this
method. When metal samples are exposed to the
atmosphere, they are susceptible to corrosion.
• Tooth enamel and dentine have been examined
by x-ray diffraction.
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49. Reference
• Chatwal R G, Anand K S, “Instrumental method of
chemical analysis”, Himalaya publishing house, Page
no:2.303-2.339
• Kamboj C P, “Pharmaceutical analysis- 2 instrumental
method” , Vallabh publication, page no:461-483.
• Aaltonen, J.; Alleso, M.; Mirza, S.; Koradia, V.;
Gordon, K. C.; Rantanen, J. Solid Form Screening—A
Review. Eur. J. Pharm. Biopharm. 2009, 71, 23–3.
• Andreeva, P.; Stoilov, V.; Petrov, O. Application of X-
ray Diffraction Analysis for Sedimentological
Investigation of Middle Devonian Dolomites from
Northeastern Bulgaria. Geol. Balcanica 2011.
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