IGCAR : Annual Report - Indira Gandhi Centre for Atomic Research

IGC
Annual Report 2007
characterization of the crystals
and even today it is the first step
in assessing the crystal quality.
In the Laue camera, instead of
the photographic X-ray film an
imaging plate cut in a circular
shape is loaded and covered
with an opaque paper. The
exposed plates are scanned to
obtain the image. The Laue
diffraction pattern for Si crystal
in both transmitted and back
reflected geometries are given
in Fig.1. The inset in Fig. 1
shows the enlarged view of a
particular Laue spot which
depends on the nature of the
crystal.
The powder XRD experiment
was carried out using the
imaging plate for a BaF 2
standard sample. The sample
was kept in front of the
collimator in Debye Scherrer
geometry and the imaging plate
kept at a distance of 77.6 mm
from the sample. Mo K X-ray
°
with a wavelength of 0.709 A is
used for this experiment. The
Fig.2 Powder diffraction pattern of BaF 2 sample; with some isolated
diffraction spots along the Debye rings indicated using the small circles
in the images. The blue circle and the arc shows the psi angle
XRD image obtained is shown
in figure 2. The sample was
well powdered before carrying
out the diffraction experiment.
In spite of this there are a few
isolated diffraction spots
(shown by the circles in the
image) in the powder pattern
indicating the coarse grained
nature of the sample. This 2D
pattern is converted into a 1D
pattern by azimuthal integration
of pixel intensities from 0 to
360° and by increasing the
radius value from the centre of
the concentric rings to the edge
of the plate (2000 units). The
center point of the rings is
identified by triangulation of
Fig.2 Powder diffraction pattern of BaF 2 sample; with some isolated
diffraction spots along the Debye rings indicated using the small circles
in the images. The blue circle and the arc shows the psi angle
three points of any one of the
rings. This centre is a crucial
factor in the 1D data quality
hence its accurate location is
essential. In order to compare
the integrated data with that
collected using a standard
powder diffractometer (with a
point detector), the intensity of
every 2 step is normalized by
the number of pixels
contributing to it. Also in the
converted data there is high
background hence it is
removed from the image using
an algorithm. The as acquired
XRD image and the background
subtracted image are shown in
Fig. 2 and the inset (intensity
plot along the circumference of
the ring) shows the coarse
grained nature in the sample.
The converted 1D pattern
before and after removing the
background is shown in figure
3. The conclusion is that if
there is a single crystal
diffractometer with area
detector like imaging plate the
same could be used for powder
diffraction experiments.
BASIC RESEARCH 167