x-ray-diffraction-technique

X- Ray Diffraction
Presentation
By
Archana
M.Pharmacy (Pharmaceutics)
GPRCP
1
Ch.Archana,M.Pharmacy(Pharmaceutics),Roll no:15

CONTENTS
 INTRODUCTION
 GENERATION OF X-RAYS
 PRINCIPLE
 INSTRUMENTATION
 METHODS
 APPLICATIONS
 CONCLUSIONS
 REFERENCES
Ch.Archana,M.Pharmacy(Pharmaceutics),Roll no:15 2

INTRODUCTION:
X-rays were discovered by Wilhelm Roentgen
who called them x-rays because the
nature at first was unknown so, x-rays
are also called Roentgen rays. X-ray diffraction
in crystals was discovered by Max von Laue. The
wavelength range is 10-7 to about 10-15 m.
The penetrating power of x-rays depends on
energy also, there are two types of x-rays.
i) Hard x-rays: which have high frequency and
have more energy.
ii) soft x-rays: which have less penetrating and
have low energy
Max Von
Laue
3

X-RAYS
1.X-rays are short wave length electromagnetic radiations
produced by the deceleration of high energy electrons
or by electronic transitions of electrons in the inner
orbital of atoms
2.X-ray region 0.1to100 A˚
3.Analytical purpose 0.7 to 2 A˚

PRINCIPLE
X-ray diffraction is based on constructive
interference of monochromatic x-rays and a crystalline
sample. These x-rays are generated by a cathode ray
tube, filtered to produce monochromatic radiation
,collimated to concentrate and directed towards the
sample. The interaction of incident rays with the
sample produces constructive interference when
conditions satisfy Bragg’s law.

BRAGG’s EQUATION
d




Ray 1
Ray 2

Deviation = 2
 The path difference between ray 1 and ray 2 = 2d Sin
 For constructive interference: n = 2d Sin
6
Ch.Archana,M.Pharmacy(Pharmaceutics),Roll
no:15

“Constructive interference of the reflected beams
emerging from two different planes will take place if
the path lengths of two rays is equal to whole number
of wavelengths”.
for constructive interference,
nλ=2dsin
this is called as BRAGG’S LAW
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no:15

INSTRUMENTATION
 Production of x-rays
 Collimator
 Monochromator
a.Filter
b.Crystal monochromator
 Detectors
a.Photographic methods
b.Counter methods
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no:15

Instrumentation of XRD

PRODUCTION OF X-RAYS:
X-rays are generated when high velocity electrons
impinge on a metal target.
Approximately 1% of the total energy of the electron
beam is converted into x-radiation.
The remainder being dissipated as heat.
Many types of x-ray tubes are available which are used
for producing x-rays.

Coolidge tube
 a . Positive voltage in the form of anode having a target
a
• b . Battery to emit thermoionic electrons
• C. Cathode –filament of tungsten metal
• The electrons are accelerated towards the target a
• On striking the target the electrons transfer their
energy to its metallic surface which gives off x-ray
radiation
11
b c a

COLLIMATOR:
 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 gap.

TYPES OF MONOCHROMATORS
13
In order to do monochromatization,2 methods are
available
1.Filter
2.Crystal monochromator
a)Flat crystal monochromator
b)Curved crystal monochromator
Materials used-Nacl,quartz etc,.

A.FILTER: X-ray beam may be partly
monochromatized by insertion of a
suitable filter
A filter is a window of material that
absorbs undesirable radiation but
allows the radiation of required
wavelength to pass
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•2)CRYSTAL MONOCHROMATOR : Crystal monochromators is
made up of suitable crystalline material positioned in the x-ray
beam so that the angle of reflecting planes satisfied the Bragg’s
equation for the required wavelength
the beam is split up into component wavelengths
crystals used in monochromators are made up of materials like
Nacl, lithium fluoride , quartz etc.
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DETECTORS
 The x-ray intensities can be measured and recorded either by
 1)Photographic methods
 2)Counter methods
 a) Geiger - Muller tube counter
 b) Proportional counter
 c) Scintillation detector
 d) Solid state semi conductor detector
 e) Semi conductor detectors
 Both these types of methods depends upon ability of x-rays to ionize
matter and differ only in the subsequent fate of electrons produced
by the ionizing process.

 Photographic method: To record the position and intensity
of x-ray beam a plane or cylindrical film is used
 The film after exposing to x-ray is developed
 The blackening of the developed film is expressed in terms
of density units D given by
D=log I₀/I
I₀- incident intensities
I- transmitted intensities
D-Total energy that causes blackening of the film
D is measured by densitometer
The photographic method is mainly used in diffraction
studies since it reveals the entire diffraction pattern on a
single film .
Dis advg: time consuming and uses exposure of several hours
no:15 17

 COUNTER METHODS:
 a) Geiger - Muller tube counter
Geiger tube is filled with inert gas like argon
Central wire anode is maintained at a positive potential of
800 to 2500V .
X-RAY Collision with filling gas Production of
an ion pair
Electon-central
anode
Positive
ion-moves
to outer
electrode
The electron is accelerated by the potential gradient and
causes the ionisation of large number of argon atoms
,resulting in the production of avalanche of electrons that
are travelling towards central anode
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b)PROPORTIONAL COUNTER:
 Construction is similar to Geiger tube counter
 Proportional counter is filled with heavier gas like
xenon and krypton
 Heavier gas is preferred because it is easily ionized
 Operated at a voltage below the geiger plateau
 The dead time is very short (~0.2μs), it can be used to
count high high rates without significant error.
no:15 19

C)SCINTILLATION DETECTOR:
 In a scintillation detector there is large sodium iodide
crystal activated with a small amount of thallium
 When x-ray is incident upon crystal , the pulses of
visible light are emitted which can be detected by a
photo multiplier tube
 Useful for measuring x-ray of short wavelength
 Crystals used in scintillation detectors include sodium
iodide , anthracene ,napthalene and p-terphenol
ixylene.
 The dead time is short
no:15 20

d)Solid state semi-conductor detector
 In this type of detector ,the electrons produced by
x-ray beam are promoted into conduction bands
and the current which flows is directly
proportional to incident x-ray energy
 Dis advantage:
 Semi – conductor device should be maintained at
low temperatures to minimize noise and prevent
deterioration
no:15 21

e)semi-conductor detectors:
 When x-ray falls on silicon lithium drifted detector an electron (-e) and a hole
(+e)
 Pure silicon made up with thin film of lithium metal plated onto one end
 Under the influence of voltage electrons moves towards +ve charge and holes
towards –ve
 Voltage generated is measure of the x-ray intensity falling on crystal
 Upon arriving at lithium pulse is generated
 Voltage of pulse=q/c; q-tot charge collected on electrode, c-detector capacity.
no:15 22

X-RAY DIFFRACTION METHODS
These are generally used for investigating the internal
structures and crystal structures of various solid
compounds.
They are
1.Laue’s photographic method
a)Transmission method
b)Back reflection method
2.Bragg’s X-ray spectrometer method
3.Rotating crystal method
4.Powder method

X-Ray Diffraction Method
Laue Rotating Crystal Powder
no:15 24
Orientation
Single Crystal
Polychromatic Beam
Fixed Angle
Lattice constant
Single Crystal
Monochromatic Beam
Variable Angle
Lattice Parameters
Polycrystal (powdered)
Monochromatic Beam
Variable Angle

25
a)Transmission Laue method
In the transmission Laue method, the film is placed behind the crystal to record
beams which are transmitted through the crystal.
One side of the cone of Laue reflections is defined by the transmitted beam. The
film intersects the cone, with the diffraction spots generally lying on an ellipse.
•Can be used to orient crystals for solid state experiments.
•Most suitable for the investigation of preferred orientation sheet particularly
confined to lower diffraction angles.
•Also used in determination of symmetry of single crystals.

b)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.
 One side of the cone of Laue reflections is defined by the transmitted beam. The film
intersects the cone, with the diffraction spots generally lying on an hyperbola.
 This method is similar to Transmission method however, black-reflection is the only
method for the study of large and thick specimens.
 Disadvantage:
 Big crystals are required
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no:15

 Crystal orientation is determined from the
position of the spots. Each spot can be indexed,
i.e. attributed to a particular plane, using
special charts.
 The Greninger chart is used for back-reflection
patterns and the Leonhardt chart for
transmission patterns.
 The Laue technique can also be used to assess
crystal perfection from the size and shape
no:15 27

The Bragg’s x-ray spectrometer method:
 Laue-beam of x-ray-crystal-emitted x-ray obtained on
photographic plate-using photograph-brag analysed
structures of crystals of Nacl,Kcl,and Zns-brags equation
 Single plane generates several diffraction lines-sum tot of
diffraction lines gives diffraction patterns-from the pattern
we can deduce different distances between planes-angle
between planes in each of three dimensions
no:15 28
source

The Bragg’s x-ray spectrometer method:
 A-anti cathode
 B-B’ – Adjustable slits
 C-crystal
 E-ionization chamber
 One plate of ionization chamber is connected to the
positive terminal of a H.T Battery , while negative terminal
is connected to quadrant electrometer(measures the
strength of ionization current)
no:15 29

The Bragg’s x-ray spectrometer method
Working:
 Crystal is mounted such that ѳ=0° and ionization chamber
is adjusted to receive x-rays
 Crystal and ionization chamber are allowed to move in
small steps
 The angle through which the chamber is moved is twice
the angle through which the crystal is rotated
 X-ray spectrum is obtained by plotting a graph between
ionization current and the glancing angleѳ
 Peaks are obtained.peaks corresponds to Bragg’s reflection
 Different order glancing angles are obtained with known
values of d and n and from the observed value of ѳ , λ can
be measured.
no:15 30

DETERMINATION OF CRYSTAL STRUCTURE BY BRAGG,S LAW
 X-Rays falls on crystal surface
 The crystal is rotated and x-rays are made to reflect
from various lattice planes
 The intense reflections are measured by bragg’s
spectrometer and the glancing angles for each
reflection is recorded
 Then on applying bragg’s equation ratio of lattice
spacing for various groups of planes can be obtained.
 Ratio’s will be different for different crystals
 Experimentally observed ratio’s are compared with the
calculated ratio’s ,particular structure may be
identified.
no:15 31

ROTATING CRYSTAL METHOD:
Photographs can be taken by :
 1.Complete rotation method:in this method series of complete revolutions
occur
 Each set of a plane in a crystal diffracts four times during rotation
 Four diffracted beams are distributed into a rectangular pattern in the central
point of photograph
 2.Oscillation method:the crystal is oscillated at an angle of 15° or 20°
 The photographic plate is also moved vack and forth with the crystal
 The position of the spot on the plate indicates the orientation of the crystal at
which the spot wasformed
no:15 32

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, homogenized, and average
bulk composition is determined.
Fine powder is struck on a hair with a gum ,it is suspended vertically in the axis of a
cylindrical camera
 When monochromatic beam is allowed to pass different possibilities may happen
1. There will be some particles out of random orientation of small crystals in the fine
powder
2. Another fraction of grains will have another set of planes in the correct positions for
the reflections to occur
3. Reflections are possible in different orders for each set
no:15 33

 If the angle of incidence is ѳ then the angle of reflection
will be 2ѳ
 If the radius is r the circumference 2πr corresponds to a
scattering angle of 360°
Ѳ=360*1/πr
 From the above equation the value of ѳ can be calculated
and substituted in bragg’s equation to get the value of d
 Applications
 Useful for determining the complex structures of metals
and alloys
 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
no:15 34

APPLICATIONS OF XRD
1. Structure of crystals
2. Polymer
characterisation
3. State of anneal in metals
4. Particle size
determination
a) Spot counting method
b) Broadening of
diffraction lines
c) Low-angle scattering
5.Applications of diffraction
methods to complexes
a) Determination of cis-trans
isomerism
b) Determination of linkage
isomerism
6.Miscellaneous applications
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no:15

1.STRUCTURE OF CRYSTALS
a-x-ray pattern of salt Nacl
b-x-ray pattern of salt Kcl
c-x-ray pattern of mixture of
Nacl &Kcl
d-x-ray pattern of a powder
mixed crystal of Nacl & Kcl
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no:15

2.POLYMER CHARACTERISATION
 Determine degree of crystanillity
 Non-crystalline portion scatters x-ray beam to give a
continuous background(amorphous materials)
 Crystalline portion causes diffraction lines that are not
continuous.(crystalline materials)
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no:15

38
3.State of anneal in metals:XRD is used to to test the
metals without removing the part from its position and
without weakening it.
4.PARTICLE SIZE DETERMINATION
Spot counting method:
v=V.δθ.cosθ/2n
V=volume of individual crystallite
V=total volume irradiated
n=no. of spots in diffraction ring
δθ =divergence of x-ray beam
no:15

MISCELLANEOUS APPLICATIONS
 Soil classification based on crystallinity
 Analysis of industrial dusts
 Assessment of weathering & degradation of
minerals & polymers
 Study of corrosion products
 Examination of tooth enamel & dentine
 Examination of bone state & tissue state
 Structure of DNA&RNA
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no:15

CONCLUSIONS
 For materials including metals, minerals, plastics,
pharmaceuticals and semiconductors XRD
apparatus provide highly accurate tools for non-destructive
analysis.
 The diffraction systems are also supported by an
extensive range of application software
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no:15

X-ray diffraction pattern for a single alum crystal.
41

X-ray diffraction image of a
crystal of lysozyme
42
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43
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44
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Bruker's X-ray Diffraction D8-Discover instrument

REFERENCES
1)Instrumental methods of chemical analysis ,B.K.sharma,17th
edition 1997-1998,GOEL publishing house.page no:329-359
2)Principles of instrumental analysis,5th edition ,by Dougles
a.skoog,f.James holles,Timothy A.Niemen.page no:277-298
3)Instrumental methods of chemical analysis ,Gurudeep
R.chatwal,sham k.anand,Himalaya publications page no:2.303-
2.332
4) http://www.scienceiscool.org/solids/intro.html
5) http://en.wikipedia.org/wiki/X-ray_crystallography
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no:15 47

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