X ray diffraction(xrd) principle and use

X-RAY
DIFFRACTION(XRD)
A PRESENTATION
ON
Submitted to-
Dr. Sonal Tripathi
Associate Professor
Dept. of Soil Science
N.M.C.A., NAU, Navsari
Submitted by-
Srikumar Debasis Swain
1st year M.Sc. (Agri)
2nd semester
Dept.- Agronomy
Regd. No.- 2010117110

INTRODUCTION
• It is a novel and non-destructive method of chemical analysis
meaning the chemical substance is not affected by the
analysis.
• The atomic planes of a crystal cause an incident beam of X-
rays to interfere with one another as they leave the crystal.
The phenomenon is called X-ray diffraction.
• Every crystalline substance gives a pattern; the same
substance always gives the same pattern; and in a mixture of
substances each produces its pattern independently of the
others.
• The X-ray diffraction pattern of a pure substance is,
therefore, like a fingerprint of the substance. It is based on
the scattering of x-rays by crystals.

WHAT IS X-RAY ?
• X-rays are electromagnetic radiation of wavelength about 1 Å (10-10m)which is
about the same size as an atom.
• They occur in that portion of the electromagnetic spectrum between gamma
rays and the ultraviolet.
• The discovery of X-rays in 1895 enabled scientists to probe crystalline structure
at the atomic level.
If we use a white light we cannot look
at objects smaller than the wavelength
of light, which is about 10 -6 m. Since
the atom has dimensions of about 10-10
m we cannot image an atom with a
photon of white light. X-rays, on the
other hand, have a wavelength of about
10 -10 m and are suitable for imaging
objects at the atomic scale.
WHY X-RAY IS
USED

GENERATION OF X-RAYS
 X-rays can be generated by decelerating electrons.
 Hence, X-rays are generated by bombarding a target (say Cu) with an electron beam.
 The resultant spectrum of X-rays generated (i.e. X-rays versus Intensity plot) is shown
in the next slide. The pattern shows intense peaks on a ‘broad’ background.
 The intense peaks can be ‘thought of’ as monochromatic radiation and be used for
X-ray diffraction studies.
Beam of electrons Target X-rays
An accelerating (or
decelerating) charge
radiates
electromagnetic
radiation

WHY XRD ?
 Measure the average spacing's between layers or rows of atoms
 Determine the orientation of a single crystal or grain
 Find the crystal structure of an unknown material
 Measure the size, shape and internal stress of small crystalline regions
X-RAY
SOURCES
the sealed-
tube
the rotating
anode

Sealed tube
The sealed tube is simply a glass or ceramic tube where a tungsten cathode has been
placed above a metallic stationary anode. The tube is then evacuated and current is
applied to the cathode and the anode
Rotating anode
A rotating anode is similar to the sealed tube instrument except for the fact that the metallic
anode is now spinning. The spinning anode spreads the heat of the electron bombardment
over a wider area. This allows for higher wattages, which produces a higher X-ray flux.
For diffraction experiments the X-rays should be monochromatic.
The crystal
monochromator
produces more
monochromatic X-rays
at the expense of X-ray
flux.
The metallic filter is
normally used with
powder diffraction
and results in high
X-ray flux with poor
monochromation.
To do this we employ either a crystal monochromator or a metallic filter.

The anode is also rectangular which allows for a line focus (which is broad but
has low flux and a point focus, which is intense but has a narrow illumination
area. In practice the line focus is used with powder diffraction so as to
illuminate more sample and the point focus is used in single crystal and
small angle x-ray scattering instruments for higher flux for small samples.

X ray diffraction(xrd) principle and use

The X-rays that are generated are of two types
1) Characteristic (ejection of electrons from the atom in the anode
2) White Radiation (synchrotron effect)
Electron strikes the
target and ejects an
electron. The cascade
of electrons from
higher orbitals
generates X-ray
M
Characteristic
X-rays
Kalpha Kbeta
Electron reaccelerate
when entering the metal
and "bend" their
trajectory path. Loss of
momentum results in
generation of X-rays.
M
White Radiation
“Bremsstrahlung”
or breaking
radiation

The energy of the X-ray is determined from the observed wavelength and is
given by the formula :
Energy (KeV) = 1.2398 / λ (nm)
Intensity
Wavelength ()
0.2 0.6 1.0 1.4
White
radiation
Characteristic radiation →
due to energy transitions
in the atom
K
K
Intense peak, nearly
monochromatic
Energy for K alpha (for Mo) = 17.28 KeV
Mo Target impacted by electrons
accelerated by a 35 kV potential shows
the emission spectrum as in the
figure(schematic)
X-ray sources with different 
for doing XRD studies
Target
Metal
 Of K
radiation (Å)
Mo 0.71
Cu 1.54
Co 1.79
Fe 1.94
Cr 2.29

X-ray sources with different  for doing XRD studies
Elements (KV)  Of K1
radiation
(Å)
 Of K2
radiation (Å)
 Of Kβ
radiation (Å)
Kβ-Filter
(mm)
Ag 25.52 0.55941 0.5638 0.49707 Pd
0.0461
Mo 20 0.7093 0.71359 0.63229 Zr
0.0678
Cu 8.98 1.540598 1.54439 1.39222 Ni
0.017
Ni 8.33 1.65791 1.66175 1.50014 Co
0.0158
Co 7.71 1.78897 1.79285 1.62079 Fe
0.0166
Fe 7.11 1.93604 1.93998 1.75661 Mn
0.0168
Cr 5.99 2.2897 2.29361 2.08487 V
0.169

WORKING PRINCIPLE
 A beam of X-rays directed at a crystal interacts with the electrons of the atoms in the crystal.
 The electrons oscillate under the influence of the incoming X-Rays and become secondary sources
of EM radiation.
 The secondary radiation is in all directions.
 The waves emitted by the electrons have the same frequency as the incoming X-rays  coherent.
 The emission can undergo constructive or destructive interference.
Incoming X-rays
Secondary
emission
Oscillating charge re-radiates  In phase with
the incoming x-rays
Sets Electron cloud into oscillation
Sets nucleus into oscillation
Small effect  neglected

BRAGGS’ LAW Braggs’ law is followed because here diffraction can
be visualised as reflection
 The scattering planes have a spacing ‘d’.
 Ray-2 travels an extra path as compared to Ray-1 (= ABC). The path difference between
Ray-1 and Ray-2 = ABC = (d Sin + d Sin) = (2d.Sin).
 For constructive interference, this path difference should be an integral multiple of :
n = 2d Sin  the Bragg’s equation. (More about this sooner).
 The path difference between Ray-1 and Ray-3 is = 2(2d.Sin) = 2n = 2n. This implies
that if Ray-1 and Ray-2 constructively interfere Ray-1 and Ray-3 will also constructively
interfere. (And so forth).

Understanding the Bragg’s equation
 n = 2d Sin
The equation is written better with some descriptive subscripts:
 n is an integer and is the order of the reflection
(i.e. how many wavelengths of the X-ray go on to make the path difference between planes).
Note: if hkl reflection (corresponding to n=1) occurs at hkl then 2h 2k 2l reflection (n=2) will occur at a higher angle 2h 2k 2l.
  For large interplanar spacing the angle of reflection tends towards zero → as d increases,
Sin decreases (and so does ).
 The smallest interplanar spacing from which Bragg diffraction can be obtained is /2 →
maximum value of  is 90, Sin is 1  from Bragg equation d = /2.
2 SinCu K hkl hkln d 
Order of the reflection (n)
 For Cu K radiation ( = 1.54 Å) and d110= 2.22 Å
n Sin = n/2d 
1 0.34 20.7º • First order reflection from (110)  110
2 0.69 43.92º
• Second order reflection from (110) planes  110
• Also considered as first order reflection from (220) planes  220

Relation between dnh nk nl and dhkl
2 2 2
Cubic crystal
hkl
a
d
h k l

 
8
220
a
d 
2
110
a
d 
2
1
110
220

d
d
2 2 2
( ) ( ) ( )
nhnk nl
a
d
nh nk nl

 
2 2 2
hkl
nhnk nl
da
d
nn h k l
 
 
110
220
2
d
d 
2 sinhkl hkln d 
 sin2
n
dhkl

n n n n n n2 sinh k l h k ld 
1nhnk nl
hkl
d
d n


A modern automated x-ray diffractometer
X-
ray
tube
Detector

Basic components & Features of XRD
Production
Diffraction
Detection
Interpretation

Detection of Diffracted X-rays by a Diffractometer
Bragg - Brentano Focus Geometry, Cullity

Clay prep. And analysis
• Clay fraction needs to be separated (by size) for detailed analyses – mix sample in
water, clays will be suspended, decant and centrifuge liquid to concentrate the clays
• Several methods for mounting the clays – need to orient them flat
• Depending on the type of clay, further preparation is needed
Methods include:
 Solvating with ethylene glycol or glycerol (replaces water – gives a constant
interlayer spacing)
 Baking at various high temperatures to destroy parts of the crystal structure
 Saturating with cations (Mg, K, etc.) may produce diagnostic structural changes
14Å, 10Å, 7Å Clay Groups
 Smectites (shrinking-swelling clays) 14+Å, greater than 14Å if interlayer water
 Chlorite 14Å and 7Å peaks
 Kaolinite 7Å peak
 10Å clays are Micas, Illite or Glauconite
 Vermiculite 14Å and
 Å depending on Mg, Na, Fe

X ray diffraction(xrd) principle and use

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