Synchrotron X-ray polycrystalline diffractometry

Results using parallel-beam polycrystalline geometry at the Stanford Storage Ring are compared with conventional X-ray tube focusing. The PC-automated instrumentation included a pair of vertical-scan diffractometers for wavelength selection using a Si(111) channel monochromator and for powder specimens which may be measured in reflection or transmission. The dependence of intensity, profile shape, width and position on instrument parameters is described. All the profiles in patterns of well crystallized specimens with a selected receiving slit are symmetrical and primarily Gaussian with nearly the same width, thereby greatly simplifying the algorithms and programs for profile fitting and interpretation of profile broadening. The easy wavelength selection allows the use of a wavelength just longer than the absorption edge of elements in the sample to obtain maximum P/B ratio, and short wavelengths permit access to very high hkls. Because of the absence of the Kα doublet and the simple symmetrical profile shape the resolution need not be as good as in focusing geometry to achieve comparable overlap separation. The average precision of lattice-parameter determination was Δd/d = 5.6 × 10⁻⁵ using forward reflections.