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Crystal builder

The crystal builder dialogue allows to generate interactively crystal structures (Fig. 1).

Figure1

Figure 1 Crystal builder.

The 3-D crystal structure displayed is generated from the space-group, lattice parameters and the 5 atoms of the table. The complete orbit (equivalent atoms) of Al at Wyckoff position h is displayed in colored in white. Defining a new structure requires the knowledge of the space-group, lattice parameters and atoms position.

The space-group and lattice parameters are defined using the spaceGroup tool button.

Figure2

Figure 2 Space-group and lattice parameters.

During the generation of the unit cell, the selected area diffraction pattern can be plotted with the spotPattern tool button. The other tools (from left to right) are used to:

Figure3

Figure 3 Space-group dialogue.

Figure4

Figure 4 Atom dialogue to define a new orbit of atoms.

In order to add an atom to the unit cell, it is necessary to set the atom symbol before specifying its (x, y, z) fractional coordinates. The Wyckoff position of the atom (a, b, c, ...) uniquely defines the frational coordinates of equivalent or orbit related atoms. Figure 5 shows a tabular list of the unit cell atoms.

Figure5

Figure 5 Atoms of the unit cell.


The tool buttons at the bottom of the table (from left to right) allow to:

The Wyckoff positions are provided by the System tab (Fig. 6). This tab also tabulates the space-group and point-group symmetry operations. Atom Co of Figure 5, being at Wyckoff position d, initial fractional coordinates (x, y, z) are automatically defined. Furthermore it is only necessary to explicitely set the x coordinate of atom Al in Wyckoff position h since coordinate y = 2x and z = 1/4.

Figure6

Figure 6 Wyckoff positions of space-group P 63/m 2/m 2/c.

The Atoms tab also allows to show the atoms bonds (Fig. 7), to change the resolution of the spheres and/or bonds (Resolution tab) and to change the atoms color and size (Species tab).

Figure7

Figure 7 Al5Co2 unit cell with Al-Co bonds and the Al k orbit.

Figure8

Figure 8 Builder frame drawing tab.

The Drawing tab controls the view type (perspective or projection). When the unit cell is hexagonal, 3 unit cells can be displayed in order to better see the crystal structure (Fig. 9). The magnification of the projection or perspective view is selectable in the Zoom tab.

Figure9

Figure 9 [0, 0, 1] projection view of Al5Co2 (3 unit cells and orbit of Co atom at Wyckoff position h).


The Duplicate tab allows to duplicate the unit cell (Fig. 10) by 2, 4 or 8. Other duplication factors are obtained using the make tool button.

Figure10

Figure 10 [0, 0, 1] projection view of Al5Co2 (2 x 2 duplicated unit cells and orbit of Co atom at Wyckoff position h). After duolication the unit cell is triclinic.

The sterographic projection makes possible to display the structure in many [uvw] orientations (Fig. 11).

Figure11

Figure 11 [1,1,0] projection view of the 2 x 2 x 2 duplicated (and shown as hexagonal) structure.

At any building stage of the unit cell a SAED pattern can be plotted (Fig. 12).

Figure12

Figure 12 [1,1,0] kinematical SAED pattern.