Fyzikální ústav Akademie věd ČR

Department of structure analysis investigates crystalline materials. They are characterized by regular atomic arrangement, so called translation periodicity, which can be found in three dimensions (classical crystallography) or in more dimensional space (crystallography of aperiodic structures). Both kinds of materials are investigated with help of x-ray or electron diffraction and the diffraction data are processed with our own computing system Jana, the world-wide respected tool for calculation of complicated crystal structures.

Development of the program Jana is our most important theoretical output. Step by step all branches of crystallography are incorporated in the program with aim to develop a universal tool for studies of crystal structures, from trivial ones to very complicated cases. Jana enables combination of various kinds of diffraction data. Therefore it can serve as a general calculation tool for all diffraction methods used in our department.

In experimental area the main focus is on complementarity of methods in order to be able to investigate variety of materials: single crystals with classical x-ray diffraction and structure analysis; powders with powder diffraction and Rietveld refinement; micro-samples with precession electron diffraction. The only way of solution for many complicated materials is combination of those methods. Unique computation tools based in the program Jana are very helpful for any combination of diffraction methods.

The atomic structure has an impact on their electronic and magnetic properties which can be measured with spectroscopic methods. Analysis of x-ray spectra provides structure information even in cases when usage of diffraction methods is limited (glasses, clusters, boundaries). The theoretical group - an important part of the department - analyses x-ray spectral data, makes quantum-mechanical calculations of total energies from the first principles and studies hardness of materials.

Another area supported by the department is a service provided by laboratory of electron microscopy in the field of quantitative and qualitative elementary analysis and surface morphology. Another often required service is orienting of single crystals with help of Laue or precession photographic method.

Three basic diffraction methods illustrated with help of Ewald sphere and reciprocal crystal lattice. The diffraction occurs when a point of the reciprocal lattice meets the surface of the Ewald sphere. (1) Diffraction with single crystal requires sample rotation in order to bring maximum of the reciprocal lattice points to the surface of the Ewald sphere. (2) Diffraction with powder sample can be done without sample rotation because each grain possesses a randomly oriented crystal lattice. (3) Electron diffraction requires sample rotation. Ewald sphere is very large due to short wavelength of the electrons. Therefore multiple diffraction of many reciprocal lattice points is highly probable. In order to minimize multiple diffraction the incoming electron beam makes a precession movement. (4) The logo of the program Jana in the centre symbolizes unified processing of all the mentioned kinds of diffraction data by this program.