2. Introduction
• It is a novel & non destructive method of chemical analysis and
a variety of x –ray techniques are available in practice.
• These are : X – Ray Absorption : X-ray diffraction
X-ray Fluorescence
• “ Every crystalline substance gives a pattern; the same substance
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• “ 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”.
7. Why to select XRD?
• Measure the average spacing's between layers of atoms.
• Determine the orientation of a single crystal.
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• Find the crystal structure of an unknown material.
• Measure the size, shape and internal stress of small
crystalline regions.
8. What is Crystallography???
• The atoms are arranged in a regular
pattern, and there is as smallest volume
element that by repetition in three
dimensions describes the crystal. This
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dimensions describes the crystal. This
smallest volume element is called a unit
cell.
• The dimensions of the unit cell is
described by three axes : a, b, c and the
angles between them α, β , and γ are
lattice constants which can be
determined by XRD.Lattice
9. Diffraction Conditions
Fraunhofer diffraction Bragg diffraction
}d
}d
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For constructive
interference,
d sin = n
For constructive
interference,
2(d sin) =n
d
}
}
d
d sin
}
}d
d sin d sin
10. How X-rays are Produced???
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X-rays are produced whenever high-speed electrons collide with a metal
target. A source of electrons – hot W filament, a high accelerating voltage
between the cathode (W) and the anode and a metal target, Cu, Al, Mo,
Mg.
13. D8 ADVANCE Bragg-Brentano
Diffractometer
• A scintillation counter may be
used as detector instead of film
to yield exact intensity data.
• Using automated goniometers
step by step scattered intensity
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step by step scattered intensity
may be measured and stored
digitally.
• The digitised intensity may be
very detailed discussed by
programs.
• More powerful methods may be
used to determine lots of
information about the specimen.
16. Experimental XRD data are compared to
reference patterns to determine what
phases are present
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The reference patterns are represented by sticks
the position and intensity of the reference sticks
should match the data.
A small amount of mismatch in peak position and
intensity is acceptable experimental error.
21. All calculations are more accurate if you use more
peaks over a longer angular range
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If you use one or two peaks, you must assume:
– That there is no specimen displacement error when calculating lattice
parameters
– That there is no microstrain broadening when calculating crystallite
size.
22. If you use many peaks over a long angular range (for
example, 7+ peaks over a 60° 2theta range), you can:
Calculate and correct for specimen displacement when
solving lattice parameters.
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solving lattice parameters.
Calculate and account for microstrain broadening when
calculating crystallite size.
Improve precision by one or two orders of magnitude.
24. Applications of XRD
XRD is a non destructive technique to identify
crystalline phases.
The powder xrd pattern may be thought of as
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The powder xrd pattern may be thought of as
finger print of the single crystal structure, and it
may be used conduct qualitative and quantitative
analysis.
XRD is a technique used to determine the
orientation of the given crystal compound.
25. Obtain XRD pattern are used to measure d-spacings of
the given compound.
Determination of Cis-Trans isomerism.
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Determination of Cis-Trans isomerism.
To measure thickness of thin films and multi-layers.
To determine atomic arrangement.
