Example 2: indexation of a Laue diagram
We will describe here the steps which must be
followed during the indexation of an experimental Laue diagram.
We use as an example the one
presented by J.Laugier and A.Filhol in their
publication (see bibliography).
Select the "Crystal" button in the "Data" pulldown menu.
Choose the "Triclinic" crystal system.
Then press the "Select space group" button: this display a
sub-menu containing triclinic groups. Click on
"P -1".
Next press the "Cell parameters" button to enter the
parameters of the cell which are a=9.01, b=12.89, c=18.18,
alpha=121.8, beta=90.58, and gamma=97.3 degrees.
Select the "Detector" button in the "Data" pulldown menu.
In the new window, give a
distance from crystal to detector of 4.5 cm, and a detector size
of 18 cm x 13 cm.
Since this example is a transmission case,
click on the "Close" button to validate the data.
Use the "Spots" button in the "Data" pulldown menu.
Drag the cursor to indicate the number of
experimental Bragg spots, 6 in this example.
Next click on the "Spot coordinates" button to
enter the position for every spot (in cm) in the
detector axes (See paragraph on the set of axes):
Xd Yd
2.42 -0.02
0.44 -4.28
-3.59 -0.31
-4.51 -5.04
-3.97 2.59
-2.93 -2.11
Remember that these spots must be spots with low Miller indexes.
Although it is possible, using the "Options" button of the
"Indexation" menu, to modify the parameters used during the
indexation attempt of an experimental diagram, we
suggest to use the default values, and to
modify them only when you will
be an experienced user of laueX.
Run the indexation procedure by
selecting the "Try indexing" button of the "Indexation" pulldown menu.
It may needs some time,
depending on the speed and load of your computer:
please wait !
At the end of the indexation, the program notifies that
there are three possible solutions.
Activate the "Solutions" button of the "Indexation" menu
to display them.
In the example shown here, we note that solution 2
has the lower Miller indices for the spots.
So it is logical to try first solution 2 by clicking
on it; then press the "Close" button to
close this menu.
Select the "Options" button in the "Simulation" pulldown menu.
Choose 11 as the limits for absolute values of
h, k and l. Spots with lower hkl values only will be
drawn.
Activate the "Compute" button in the "Simulation" menu
to compute the diagram. At the end of the computation the
simulation is displayed in the drawing area.
The first two experimental spots
are indicated by crosses (x).
To obtain some informations concerning a spot,
just click on it.
When the simulation is satisfactory, i.e. when it is similar
to the experimental diagram, one may need to rotate
the crystal to align a given cristallogaphic axis
in the direction of the X-ray source.
Suppose for instance that we
want to get the [100] direction pointing towards the X-ray source.
Select the "Align" button in the "Orientation" pulldown menu.
Give [100] as direct axis in the new menu, and
click on the "Beam axis (X)" button if not yet
selected.
Then, according to the characteristics of the goniometer,
choose dependant or independant rotations.
Finally, press the "Compute possible rotations" button; the program
suggests four possible solutions. You
may choose one of them by clicking on it, and then compute a new
simulation.
Before ending laueX, it is recommanded to save your work: this will
avoid to give the same parameters
and options during a later use of the program with similar data.
Select the option "other data" of the "Save" button in the "File"
pulldown menu.
Give the name
of the file you want to create. Then click on "OK".