X-ray Crystallography
Presented By:
Biswash Sapkota
1st M-PHARM
Dept. of
Pharmacology
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Presented To:
Dr. Jaishree V
H.O.D
Department of Pharmaceutical
Analysis

Overview
•X-rays are electromagnetic waves with
wavelengths in the range of 0.01 to 10
nanometers and energies in the range of
100 eV to 100 keV.
•X-rays have shorter wavelengths
(higher energy ) than UV waves and,
generally, longer wavelengths (lower
energy) than gamma rays.
•Sometimes X-rays are called Röntgen
radiation, after Wilhelm Röntgen, who
is usually credited as their discoverer.
Fig: Electromagnetic Spectrum
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Introduction
• X-ray crystallography is a technique used for determining the atomic
and molecular structure of a crystal
• The crystalline atoms cause a beam of incident X-rays to diffract into
many specific directions.
• By measuring the angles and intensities of these diffracted beams, a
crystallographer 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 disorder, and
various other information.
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Different X-rays methods
• X-ray Absorption
• Auger Emission Spectroscopy
• X-ray Fluorescence
• X-ray Diffraction
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X-ray Absorption
•The intensity of X-ray is diminished as they
pass through material
•Wavelength at which a sudden change in
absorption occurs is used to identify an
element present in a sample, and the
magnitude of the change determines the
amount of particular element present.
•Used in elemental analysis of barium and
iodine in body
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Fig: X-ray Absorption

Auger Emission Spectroscopy (AES)
+
𝑒−
𝑒−
𝑒−
•The primary X-rays eject
electrons from inner energy
levels.
•Just outer level electrons fall
into vacant inner levels by non
radiative processes.
•Excess energy ejects
electrons from outer levels
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Fig: Auger Emission Spectroscopy

X-ray Fluorescence
+
𝑒−
𝑒−
𝑒−
•The primary X-ray
ejects electron from
inner energy levels
where the wavelength is
equal to absorption
edge.
•But when the
wavelength is shorter
than absorption edge it
emits secondary X-ray
when electrons fall into
inner vacant levels.
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Fig: X-ray Fluorescence

X-ray Diffraction Methods
• When a beam of monochromatic X radiation is directed at a crystalline
material, one observes reflection or diffraction of the X-rays at a
various angle with respect to the primary beam
• The relationship between the X-radiation, angle of diffraction and
distance between each set of atomic planes of crystal lattice is given
by Braggs condition.
nλ= 2dsinθ
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Methods
1. Laue Photographic Method
2. Bragg X-ray Spectrometer Method
3. Rotating Crystal Method
4. Powder Crystal Method
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1. Laue Photographic Method
• Laue has studied the phenomenon of diffraction of
crystal by two methods
oTransmission method and
o Back reflection method
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Transmission method
•A is a source of X-rays. This emits beams
of continuous wavelength, known as white
radiation which is obtained from a
tungsten target at about 60,000 volts.
•B is a pinhole collimator. When X-rays
obtained from A are allowed to pass
through this pinhole collimator, a fine
pencil of x-rays is obtained. This diameter
of pinhole is of importance from the stand
point of detail in diffraction pattern. The
smaller is the diameter, the sharper is the
interference.
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Fig: Laue Transmission Method

Contd..
• C is a crystal whose internal structure is
to be investigated. The crystal is set on a
holder to adjust its orientation
• D is a fine arranged on a rigid base. This
film is provided with beam stop to
prevent direct beam from causing
excessive fogging of the film.
• The x-rays are recorded on photographic
plate and study of diffraction patterns
helps to know the structure of crystal .
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Fig: Laue diagram of crystal

Back Reflection Method
• In the back-reflection method, the film is
placed between the x-ray source and the
crystal. The beams which are diffracted in a
backward direction are recorded.
• This method is similar to Transmission
method however, black-reflection is the only
method for the study of large and thick
specimens
• It is very simple and rapid and does not
involve the calculations in solving the
patterns obtained.
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Fig: Back Reflection Method

Contd..
• The main disadvantage of Laue’s method is that a big crystal is required and
furthermore there is uncertainty in significance due to unhomogenous nature of
X-rays
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2. Bragg X-ray Spectrometer method
When x-rays are scattered from a crystal lattice,
peaks of scattered intensity are observed which
correspond to the following conditions:
1.The angle of incidence = angle of scattering.
2.The path length difference is equal to an integer
number of wavelengths.
The condition for maximum intensity contained in
Bragg's law above allow us to calculate details
about the crystal structure, or if the crystal
structure is known, to determine the wavelength
of the x-rays incident upon the crystal.
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15X-ray Crystallography

Contd..
• The Braggs equation is nλ= 2dsinθ
• where n is a positive integer
• λ is the wavelength of incident wave
• d is the path length
• Θ is the incident angle
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3. Rotating Crystal Method
•The rotating crystal method was
developed by Schielbold in 1919
•The X-ray beam passed to the crystal
through collimating system
•The rotating shaft hold the crystal and it
also rotates
• This causes the sets of planes coming
successively into their reflecting
positions.
• Each plane will produce a spot on
photographic plate.
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Fig: Rotating Crystal Method

Contd..
• One can take photographs in two ways;
Complete rotation method:
In this method there occurs a series of complete revolutions. It is observed that
each set of planes in crystal diffracts four times during the rotation. These four
diffracted beams are distributed into a rectangular pattern about the central
point of photograph.
Oscillation method:
In this method, the crystal is oscillated through an angle of 15O or 200. The
photographic plate is also moved back and forth with a same period as that of
rotation of the crystal. The position of spot on the plate indicates the
orientation of crystal at which the spot was formed.
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4. Powder Crystal Method
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Fig: Powder Crystal Method
•X-ray powder diffraction (XRD) is a rapid analytical
technique primarily used for phase identification of a
crystalline material and can provide information on
unit cell dimensions.
•The analyzed material is finely ground and
homogenized
•A is a source of X-rays which can be made
monochromatic by a filter.
•Allow the X-ray beam to fall on the powdered specimen P
through the slits S1 and S2.

Contd..
• Fine powder, p, struck on a hair by means of gum is suspended vertically in the
axis of a cylindrical camera. This enables sharp lines to be obtained on the
photographic film which is surrounding the powder crystal in the form of a
circular arc.
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Contd..
• Theory: When a monochromatic beam of X-rays is allowed to fall on
the powder of a crystal, then following possibilities may happen:
 There will be some particles out of the random orientation of small
crystal in the fine powder, which lie within a given set of lattice planes
for reflection to occur.
While another fraction of the grains will have another set of planes in
the correct position for the reflections to occur and so on.
Also, reflections are also possible in the different order for each set.
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Application of X-ray Diffraction
• Characterization of crystalline materials
• Identification of fine-grained minerals such as clays and mixed
layer clays that are difficult to determine optically
• Determination of unit cell dimensions measurement of sample
purity
• Determination of Cis- trans isomerism
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Instrumentation
• This includes,
1. Production of X-rays
2. Collimator
3. Monochromator
4. Detectors
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1. Production of X-ray
• X-rays are produced inside the x-ray tube when high
energy projectile electrons from the filament interact
with the atoms of the anode .
• Conditions necessary:
Source of electrons
Target (anode)
High potential difference
Cooling facility
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Production of X-rays
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Fig : Coolidge X-ray Tube

Contd..
• There is a cathode which is a filament of tungsten metal heated by a
battery to emit the thermionic electrons.
• This beam of electrons moves towards anode and attain the kinetic
energy and 99% of energy is converted into heat via collision and
remaining 0.5-1% is converted to X-rays via strong coulomb
interactions ( Bremsstrahlung process)
• Generally the target gets very hot in use. This problem has been solved
to some extent by cooling the tube with water.
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What Happens Actually?
• If sufficiently energetic electrons are available, the transfer of energy from the
impinging electron beam may eject an electron from one of the inner levels of
the target atoms
• Within each atom, the place of the ejected electron is promptly filled by an
electron from an outer level whose place, in turn is taken by an electron
coming from still farther out
• Thus the ionized atom returns to its normal state in as series of steps, in each of
which an X-ray photon of definite energy is emitted or excess energy is
released by ejection of a second electron with characteristic energy
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Contd ..
•The k series of line is observed when an
electron in the innermost K level (n=1) is
dislodged and electrons drop down from the L
(n=2) or M (n=3) levels into the vacancy in k
level.
•Corresponding vacancies in the L levels are
filled by electron transitions from outer levels
and give rise to L series
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Fig: K series

Contd..
Disadvantage of most of X-ray tubes is that there is lack of focusing of electrons
so that whole surface becomes a source of X-rays.
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2. Collimator
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Fig: Collimator

Contd..
• The X-rays produced by the target material are randomly directed.
• They form a hemisphere with a target at the centre. In order to get a
narrow beam of X-rays, the X-rays generated by the target material are
allowed to pass through a collimator which consists of two sets of
closely packed metal plates separated by a small gap.
• The collimator absorbs all the X-rays except the narrow beam that
passes between the gaps.
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3. Monochromator
A. Filter monochromator:
• A filter is a window of material that absorbs undesirable radiation but allows
the radiation of required wavelength to pass.
• An interesting example is use of zirconium filter which is used for
molybdenum radiation.
• When X-rays emitted from molybdenum are allowed to pass through a
Zirconium filter, the Zirconium strongly absorbs the radiation of molybdenum
at short wavelengths but weakly absorbs the K alpha lines of molybdenum.
Thus, zirconium allows the K beta lines to pass.
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Contd..
B. Crystal monochromator:
• A crystal monochromator is made up of a suitable crystalline material
positioned in the X-ray beam so that the angle of reflecting planes satisfied
Bragg’s equation for the required wavelength.
• The beam is split up by the crystalline material into the component
wavelengths in the same way as a prism splits up the white light into rainbow.
Such a crystalline substance is called an analysing crystal.
• They are two types;
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Contd ..
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4. Detectors
A. Photographic methods:
• In order to record the position and intensity of X-ray beam a plane or
cylindrical film is used.
• The film after exposing to X-rays is developed. The blackening of
the developed film is expressed in terms of density units D given by
• Where, I0 and I refer to the incident and transmittance intensities of
X-rays.
• The quantity D is related to the total X-ray energy that causes the
blackening of photographic film.
• The value of D is measured by densitometer.
• This is used in diffraction studies since it reveals the entire
diffraction pattern on single film but this method is time consuming
and uses several hours
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Contd..
B. Counter methods:
• The Geiger tube is filled with an inert gas like argon and the central wire
anode is maintained at a positive potential of 800 to 2500V.
• When an X-ray is entering the Geiger tube, this ray undergoes collision with
the filling gas, resulting in the production of an ion pair: the electron produced
moves towards the central anode while the positive ions move towards outer
electrode.
• The electron is accelerated by the potential gradient and causes the ionisation
of large number of argon atoms, resulting production of an avalanche of
electrons that are travelling towards the central anode.,
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Fig : Geiger Tube

Contd ..
• The Geiger tube is in expensive and is relatively trouble free detector. This
tube gives the highest signal for given X-ray intensity.
• The disadvantages are
The efficiency of Geiger tube falls rapidly at wavelength below 1 A0
As the magnitude of the output pulse does not depend upon the energy of the
X-ray which causes ionisation, a Geiger tube cannot be used to measure the
energy of ionising radiation.
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References
• Instrumental method of analysis- Willards, 7th edition, CBS Publishers
• Instrumental method of chemical analysis- Chatwal , Himalayan
Publishing House
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