XRAY DIFFRACTION (XRD)

2. X-RAY DIFFRACTION
SPECTROSCOPY

3. CONTENTS
 INTRODUCTION
 BRAGG’S LAW
 X-RAY DIFFRACTION
 METHODS
 APPLICATIONS OF XRD
 ADVANTAGES AND DISADVANTAGES

4. INTRODUCTION:
• It is the novel and destructive method of chemical analysis and a variety
of x-ray techniques are available in practice.
These area as follows:
• X-Ray Absorption,
• X-Ray Diffraction
• X-Ray Fluorescence.
X-Ray Diffraction: "Every crystal substance gives a pattern; and in a mixture
of substances each produces its pattern independently of 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.
Definition:
The atomic planes of a crystal cause an incident beam of x-rays, to interfere
with one another as they leave the crystal. This phenomenon is known as x-
ray diffraction

6. BRAGG’S LAW
• After few months, In 1913,English Physicists Sir William Henry Bragg and
his son Sir William Lawrence Bragg developed a relationship to explain
why the cleavage faces of crystals appear to reflect X-Ray beams at certain
angles of incidence (θ).
• The variable d is the distance between atomic layers in a crystal,and the
variable λ is the wavelength of the incident X-ray beam; where ‘n’ is an
integer.

7. • Although Bragg’s law was used to explain the interference
pattern of X-rats scattered by crystals, diffraction has been
developed to study the structure of all states of matter with
any beam.
• Bragg’s carried out a series of experiments, the results of
which he published the Bragg’s Equation:
nλ=2dsinθ
Where assume n = 1 for the first order reflection.
λ = wavelength
θ = X-ray incidence angle
d = distance between atomic layers.

8. X-RAY DIFFRACTION METHODS:
• Generally, there are three methods which is used for
diffraction of X-ray:
i. Laue Method
ii. Rotating Crystal Method
iii. Powder Method
•
Orientation
Single Crystal
Polychromatic Beam
Fixed Angle
Lattice constant
Single Crystal
Monochromatic Beam
Variable Angle
Lattice Parameters
Polycrystal(powdered)
Monochromatic Beam
Fixed Angle

9. POWDER METHOD
If a powdered specimen is used, instead of a single
crystal, then there is the specimen, because there will
always be some crystals at an orientation for which
diffraction is permitted. Here a monochromatic X-
ray beam is incident on a powdered or
polycrystalline sample.
This method is used for samples that are difficult to
obtaining single crystal form.

10. • For every set of crystal planes, by chance, one or more crystals
will be in the correct orientation to give correct Bragg’s angle to
satisfy Bragg’s equation. Every crystal plane is thus capable of
diffraction. Each diffraction line is made up of a large number
of small spots, each from a spectral crystal. Each spot is so small
as to give the appearance of a continue line.

11. POWDER DIFFRACTION PATTERN

12. ADVANTAGES AND DISADVANTAGES OF X-RAYS
ADVANTAGES:
• X-ray is the most cheapest, the most convenient and
widely used method.
• X-rays are not absorbed very much air, so the specimen
need not be in an evacuated chamber.
DISADVANTAGES:
• They do not interact very strongly with lighter elements.