Croat. Chem. Acta 67 (1994) 273-288.

Powder-Pattern-Fitting Methods in Structure Determination

Biserka Grzeta^a and Hideo Toraya^b

^a Rudjer Boskovic Institute, P. O. B. 1016, HR-10001 Zagreb, Croatia
E-mail: grzeta@olimp.irb.hr
^b Ceramics Research Laboratory, Nagoya Institute of Technology, Asahigaoka, Tajimi 507, Japan

The Rietveld method is a well known powder-pattern-fitting method which consists in adjusting the complete theoretical diffraction pattern, calculated on the basis of the model for the sample crystal structure, to the experimental powder diffraction pattern. In the fitting procedure, the structure model is being refined. The Retvield method also enables determination of some other structural properties of the material, like crystallite size and strains, and the quantitative phase analysis of a multicomponent mixture. Complementary fitting methods to the Rietveld method are the individual profile fitting method and the whole-powder-pattern decomposition method, which do not require structural models. The individual profile fitting method enables decomposition of the overlapping diffraction lines in a small range of the powder pattern, while the whole-powder-pattern decomposition method simultaneously decomposes the whole powder pattern into individual lines and refines the unit-cell parameters of the sample. Although the powder-pattern-fitting methods are not methods for direct structure determination, they are very powerful tools in the course of structure determination when the sample is not available in a single crystal form. Several examples of the application of the described methods in structure determination are presented.