Powder option in Jana2000: refinement of standard and modulated structures from X-Ray and neutron powder data.

M. Dušek, V. Petříček

Institute of Physics, Academy of Sciences, Na Slovance 2, 182 21 Praha 8, Czech Republic.

Program Jana2000 is based on the generalized crystallography following from the superpace approach [1]. This provides a uniform access to both standard and modulated structures. Currently it can be applied to single crystal or powder data measured with X-rays or neutrons. The powder option was introduced in the year 2000 [2] in response to growing interest among users to refine modulated structures from powder data. After four years of development the program bears comparison with established powder systems.

The profile refinement includes refinement of cell parameters and q vectors, Gaussian, Lorentzian or Pseudo-Voight profiles, correction for anisotropic particle and strain broadening, correction for asymmetry, preferred orientation, absorption and several kinds of background description. It should be noted that no indexation tool is available. As soon as the profile fitting is finished all tools hitherto available for single crystals are activated. Jana2000 works with structures up to 6 dimensions (three q vectors) and can refine all basic structure parameters, anharmonic ADP and coefficients of anomalous dispersion. It enables modulation of occupancy, position and ADP (including anharmonic ones). For standard structures multipole refinement is available, too. The symmetry restrictions of refined parameters are calculated automatically. Powerful constraints and restrains and a flexible rigid body access can be used to build very complicated structure models. The program can also calculate, visualize and evaluate more dimensional Fourier maps, plot various parameters as a function of the internal coordinate t, calculate distances and angles, call external programs for direct methods or plotting crystal structures and many other things.

Jana2000 is free software available in www-xray.fzu.cz/jana including the source code and user manual with solved examples. In the poster we present a program scheme and two examples. The first one concerns refinement of a complicated misfit layer structure of [Ca₂CoO₃][CoO₂]_1.62 [3]. The another one shows result of rigid body refinement of P(OC₆H₅)₃) [4].

Acknowledgement

This work was supported by the Grant Agency of the Czech Republic (GA 202/03/0430).

[1] Wolff de P.M., Janssen T & Janner A.(1981). Acta Cryst. A37, 625-636.

[2] Dušek,M., Petříček,V., Wunschel,M., Dinnebier,R.,E. & Van Smaalen,S. (2001). J.Appl.Cryst. 34,398-404

[3] Grebille,D., Lambert,S., Bouree,F. & Petricek, V.(2004). J.Appl.Cryst, accepted

[4] Hernandez,O., Hedoux,A., Lefebvre,J., Guinet, Descamps,M., Papoular,R. & Masson,O. J. Appl. Cryst. (2002). 35, 212–219