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).

Entering the crystal data:

  • 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.

    Entering the detector data:

    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.

    Entering experimental spots:

    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.

    Indexation and choice of a solution:

  • 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.

    Simulation of a solution:

  • 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.

    Crystal alignment:

  • 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.

    Saving the data:

  • 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".