FORMULA FOR THE ASYMMETRIC DIFFRACTION PEAK PROFILES BASED ON DOUBLE SOLLER SLIT GEOMETRY

The asymmetric diffraction peak profiles and peak shift of conventiona l powder diffractometry systems caused by the angular divergence along the vertical axis are reproduced by asymmetrized peak profile functio ns. The asymmetrization is achieved by convoluting the angular dispers ions of both incident and scattered beams along the vertical axis. A g eneral method for mapping vertical window functions to the horizontal direction is proposed, and the formulas of two types of horizontal win dow functions mapped from symmetric double vertical Bartlett (triangul ar) and Gaussian window functions are presented. Both formulas incorpo rate a single asymmetry parameter connected with the open width of the Seller slits along the vertical direction. When experimental diffract ion peak profiles are fitted by asymmetrized pseudo-Voigt functions, t he asymmetry parameter gives good coincidence with the Sailer slit ang le, which is clearly specified in a given diffractometer. (C) 1998 Ame rican Institute of Physics. [S0034-6748(98)00806-5].