Xray Diffraction

X-ray Diffraction (XRD)
X-ray Diffraction (XRD) is a technique used to uniquely identify the crystallinty of materials
Merits of X-ray Diffraction
Measure the structural properties (strain state, grain size, epitaxy, phase composition, preferred
orientation, and defect structure).
XRD is also used to determine the thickness of thin films and multilayers, and atomic
arrangements in amorphous materials (including polymers)
XRD is noncontact and nondestructive, which makes it ideal for in situ studies.
The intensities measured with XRD can provide quantitative, accurate information on the atomic
arrangements at interfaces
In semiconductor and optical materials applications, XRD is used to measure the strain,
orientation, and defects in epitaxial thin films, which affect the film’s electronic and optical
properties.
Samples can be powder,sintered pellets coatings on substartes etc
Basics
X-rays are electromagnetic (EM) waves with wavelengths typically in the range from 0.01 nm to
a few nanometers.
This wavelength region is comparable with typical interplanar spacings in crystals.
When X-rays strike a crystal, the EM waves penetrate the crystal structure.
Each plane of atoms in the crystal reflects a portion of the waves.
The reflected waves from different planes then interfere with each other and give rise to a
diffracted beam which is at a well-defined angle 2θ to the incident beam.
Some of the incident beam goes through the crystal undiffracted and some of the beam becomes
diffracted.
The diffracted rays exist only in certain directions.
These diffraction directions correspond to well-defined diffraction angles 2θ,

The diffraction angle 2θ, the wavelength of the X-rays and the interplanar separation d of the
diffraction planes within the crystal are related through the Bragg diffraction condition,
that is, 2d sin 2θ = nλ... n = 1, 2, 3, . . …
I. the detector moves in a circle around the sample
II. the detector position is recorded as angle 2θ
III. The detector records the number of X-rays observed at each angle 2θ
IV. The X-rays intensity is usually recorded as counts or counts per second
Many powder diffractometers use the Bragg-Brentano Parafocusing geometry to keep the X-rays
beams focused, the incident angle changes in conjunction with 2theta.This is achieved by
rotating the sample or by rotating the x-ray tube.X-rays scatter from the samples or materials and
contain information about the atomic arrangement.
Diffraction occurs when light is scattered by a periodic array with long range array, producing
constructive interference at specific angles. The electrons in each atom coherently scatter light
and the strength with which an atom scatters light is proportional to the number of electrons
around the atom. Thus, atoms in a crystal are arranged in a periodic array with long-range order
and can produce diffraction. The crystal structure determines the The wavelength of X-rays is
similar to the distance between atoms in a crystal. This is the reason for atomic structure using
X-rays. The scattering of X-rays from atoms produce a diffraction pattern which contains
information about the atomic arrangement and crystal structure of a given sample. The
diffraction pattern is a product of the unique crystal pattern of a material. The crystal structure
determines the position and intensity of the diffraction peaks in an x-ray scattering position.
Interatomic distances determine the positions of the diffraction peaks while the type of atom and
positions determine the diffraction peak intensities. Diffraction peak widths and shapes are
mostly a function of instrument and microstructural parameters.
Amorphous materials do not have a periodic array of long range order so they do not produce a
diffraction pattern. Their X-ray scattering pattern features are broad , poorly defined amorphous
“humps”
X-ray scattering pattern of a sample.
Different methods of x-ray diffraction

Laue:variable wavelengths, fixed angle and only single crystals specimen can be measured.
Rotating crystal: fixed wavelengths,variable angle,single crystal
Powder:Fixed wavelength,variable angle and powder specimen
Demerits of X-ray diffraction
Only small fraction of crystallites in the sample actually contribute to the observed diffraction
pattern other crystallites are not oriented properly to produce diffraction from any planes of
atoms.
Only a small fraction of the scattered X-rays are observed by the detector-a point detector
scanning in an arc around the samples only observes one point on each diffraction cone.
Low intensity of diffracted X rays.

Xray Diffraction

Uploaded by

Copyright:

Available Formats

Xray Diffraction

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Xray Diffraction

Uploaded by

Copyright:

Available Formats

X-ray Diffraction (XRD)

Samples can be powder,sintered pellets coatings on substartes etc

Each plane of atoms in the crystal reflects a portion of the waves.

The diffracted rays exist only in certain directions.

These diffraction directions correspond to well-defined diffraction angles 2θ,

X-ray scattering pattern of a sample.

Different methods of x-ray diffraction

You might also like