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.

View full abstract

In order to investigate the availability of the Pattern Fitting Strucutre Refinement (PFSR) method for phyllo-silicates, the structure of muscovite (2M₁ type) by Jackson and West was refined. Enhancement of X-ray intensity by preferred orientation was reduced by the sample treatment with plastic aerosol and further corrected by an orientation function introduced by Rietveld. 49 parameters, including 28 positional ones, were varied with the use of both Gaussian and Lorentzian profile functions. The positional parameters obtained were mostly comparable to those of single crystal study, but some of them, 3 in the Gaussian case and 6 in the Lorentzian, were noticed to differ apparently over 3σ. This was probably due to the inadequacy of profile functions used and the incomplete reduction or correction for preferred orientation.

View full abstract