Preferred orientation correction in powder pattern-fitting

An appropriate form of the preferred orientation correction has been derived for the powder pattern-fitting based on data of the powder diffractometry with a flat specimen holder. The seven powder specimens with different average particle sizes were prepared by grinding the synthetic crystals of taeniolite, KLiMg2Si4O10F2. The intensity data were collected on an X-ray powder diffractometer with CuKα radiation, employing step scan technique. The preferred orientation factor was estimated for each reflection of the respective specimens by comparing the observed intensity with the calculated value after scaling by the least-squares procedure. The factor shows a dependence upon the acute angle φ between the preferred orientation direction and the scattering vector. To obtain an analytical expression of the correction factor, several types of functions were examined by trying to correct the effect of preferred orientation with least-squares calculations. The preferred orientation effect was satisfactorily corrected with a function of the form, p(φ)=P1+(1−P1)·exp(−P2·φ2), where P1 and P2 are parameters determined by least-squares fitting.