Two Goals in Texture Analysis

Concerning interest in texture analysis, the community of diffractionists can be roughly divided in two categories. For the first category the goal is a quantitative texture analysis. The texture can have important effects on some physical properties of manufactured materials. Consequently, the texture determination is a necessary step in material characterization. 

The traditional method to measure the pole distributions becomes unsatisfactory if the peaks are overlapped. This happens for low symmetry compounds or when the sample contains many phases. In addition, by using a position sensitive detector or neutron time-of-flight diffraction, a large segment or the whole pattern can be recorded simultaneously, and using only a small number of peaks, a large volume of information is lost. To eliminate these drawbacks, Wenk, Matthies and Lutterotti proposed a combination of the WIMV procedure (or other inversion method) with the Rietveld method - more exactly with the Le Bail (Chapter 8) routine for peak intensity extraction. In this combined method it is presumed that the structural parameters, or 

Bragg peak intensities for the random sample, are known and then are not refined. 

Those interested mostly in structure determination from powder diffraction see the texture problem differently. The presence of the preferred orientation makes a good pattern fitting difficult or even impossible and, consequently, a procedure is needed to correct for the texture effect in the Rietveld codes. For that it is not necessary to find the ODF, but to have a reliable model of the pole distribution whose parameters are refined together with the structure and other parameters. 

Later Von Dreele implemented the general description of texture by spherical harmonics in GSAS. Von Dreele proved that, by using this description, beside the robustness of the texture correction in the Rietveld method it is also possible to perform a reliable quantitative texture analysis. He measured by neutron time-of-flight diffraction a standard calcite sample previously used for a texture round robin. The patterns from different detector banks and sample orientations were processed by GSAS, refining the harmonic coefficients simultaneously with the structural and other parameters. Six pole distributions calculated from the refined harmonic coefficients and used as input in the 

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