STATE-OF-THE-ART HIGH-RESOLUTION POWDER X-RAY DIFFRACTION (HRPXRD) ILLUSTRATED WITH RIETVELD STRUCTURE REFINEMENT OF QUARTZ, SODALITE, TREMOLITE, AND MEIONITE

Abstract

Synchrotron high-resolution powder X-ray diffraction (HRPXRD) data and Rietveld structure refinements were used to examine the crystal structures of quartz, sodalite, tremolite, and meionite Me79.6, and compare them with those obtained by single-crystal diffraction (SXTL). The purpose is to illustrate that crystal structures obtained by HRPXRD are comparable to those obtained by SXTL. The comparisons indicate important and significant differences between the structures obtained by the two methods. The cell parameters obtained by Rietveld refinements using HRPXRD data appear of superior quality to those obtained by SXTL. The distances in pure SiO4 tetrahedron in quartz, sodalite, and tremolite are 1.6081(3), 1.6100(2), and 1.620(1) A, respectively. These values are affected by interstitial cations. In meionite Me79.6, the average and distances are 1.647(1) and 1.670(1) A, respectively, and they indicate that the occupancies are (Al0.28Si0.72) for T 1 where the atoms are partially ordered and (Al0.45Si0.55) for T 2 site where the atoms are nearly disordered, based on sodalite Si–O and Al–O distances of 1.6100(2) and 1.7435(2) A, respectively.