Rietveld refinement of LaB6:: data from μXRD

The Rietveld method of crystal structure refinement was an important breakthrough, allowing crystal structural information to be obtained from powder diffraction data. One remaining challenge is to collect Rietveld-quality data for polycrystalline minerals in situ, using laboratory-based micro X-ray diffraction (mu XRD) techniques. Here a new data collection method is presented, called 'multiframes', which produces high-quality data, suitable for Rietveld refinement, using the Bruker D8 DISCOVER micro X-ray diffractometer. 91 frames of two-dimensional X-ray diffraction data were collected for powdered NIST SRM 660 LaB6 standard material, using a general area-detector diffraction system (GADDS), at intervals of 0.8 degrees 2 theta. For each frame, only the central 1 degrees 2 theta was integrated and merged to produce a diffraction profile from 17 to 90 degrees 2 theta. Rietveld refinement of this data using TOPAS2 gave a unit-cell parameter (a(o)) and atomic position of boron (x) for LaB6 of 4.1549 (1) angstrom and 0.1991 (9), respectively (R-wp = 4.26, R-Bragg = 3.21). The corresponding La - B bond length was calculated to be 3.0522 angstrom. These parameters are in good agreement with the literature values for LaB6. These encouraging results suggest that Rietveld-quality micro X-ray diffraction data can be collected from the Bruker D8 DISCOVER diffractometer, provided that the GADDS detector is stepped in small increments, for each frame only the central 1 degrees 2 theta is integrated at constant arc length, and counting time is sufficient to yield adequate intensity (similar to 10 000 counts).