You can check for texture effects (preferred orientation) by obtaining multiple patterns of the material. It's realistic to expect some differences, but preferred orientation is manifest by not being able to replicate the pattern. That's the simple test. Let us know what you find. Another issue for "improper intensities" is when the specimen is not sufficiently wide enough at low angles (typically below 20-degrees 2-Theta with copper radiation) and the x-ray beam does not fully impinge on the specimen. The observed reflections in the low angle region will be less than calculated by a modelling program. Frank May Research Investigator Department of Chemistry and Biochemistry University of Missouri - St. Louis One University Boulevard St. Louis, Missouri 63121-4499 314-516-5098
________________________________ From: Gerard, Garcia S [mailto:[EMAIL PROTECTED] Sent: Wed 5/7/2008 8:57 AM To: [email protected] Subject: Preferred orientation? Dear all, I have a laboratory Bragg-Brentano X-ray (Cu) pattern that shows intensity mismatches only at low angles, ie 20-50 2theta or 1.8 to 4 Angstroms. There are overestimated peaks and also underestimated peaks.I have tried to discard factors that might cause this problem: The thermal parameters look sensible. Moreover, the data at high angle looks ok, so intensity transfer from low angle to high angle or vice versa does not seem to be the cause. Atomic positions also look sensible. And again, data at high angle looks ok. Is the scattering angle dependence of the atomic positions the same as for the thermal parameters? (I cannot remember that, but i am pretty sure it is not). Following the advice published in J. Appl. Cryst. 32, 36 (1999), the other factor that might cause this problem is preferred orientation: I have tried to find a hkl dependence in the overestimated and underestimated peaks but i could not find any. If i try to model preferred orientation with spherical harmonics the problems disappears nicely. The problem is how to justify the existence of preferred orientation. The crystal system is orthorhombic. But i have no other information that supports the existence of preferred orientation. Is there any other problem that I cannot think of?Is the preferred orientation correction masking any of these other problems I cannot think of? Regards Gerard ________________________________ Heriot-Watt University is a Scottish charity registered under charity number SC000278.
