Crystallography and XRay Diffraction
Objective :
The aim of this experiment is to determine the crystal structure of an unknown pure element
by using Xray diffraction method.
Specimens :
Unknown specimen.
Apparatus :
1. XRay Diffractometer.
2. Calculator.
Theory :
Crystal structures of elements can be classified as crystal systems. There are seven crystal
systems which are made up of different lattice parameters (Unit cell edge lengths and
interaxial angles). We can determine these crystal systems by using Xray diffraction.
Diffraction occurs when a wave encouters a series of regularly spaced obstacles, that are
capable of scattering the wave, and have distance between themselves comparable in
magnitude to the wavelengths. In addition, waves should have a certain phase relation
between themselves. A diffracted beam may be defined as a beam composed of a large
number of scattered rays mutually reinforcing one another. In diffraction, the reflection
angle (
θ29
, interplanar spacing in cubic system (d
hkl
) or wave length (
λ29
can be found by
using
Bragg’s law.
n
λ=2
d
hkl
sin
θ
( 1 29
In order to find the lattice length we can use a equation for crystal structures having cubic
symetry which is
d
hkl
=
a
(2)
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View Full Document√h²+k²+l²
Results and Discussion :
In this experiment, we have used the equation which is found by combining the Bragg’s law
equation with the equation for the lattice length.
sin²
θ
=
sin²
θ
=
λ
²
(3)
( h²+k²+l² )
s
4a²
We have obtained six 2
θ
value from the computer for an unknown element. (Xray
diffractometer has transfered the datas into the computer before.) We have used 2
θ
in above
equation as sin²
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 Spring '11
 adad
 Crystallography, Cubic crystal system, Crystal system, lattice length

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