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

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 Me(79.6), 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 < Si-O > distances in pure SiO(4) tetrahedron in quartz, sodalite, and tremolite are 1.6081(3), 1.6100(2), and 1.620(1) angstrom, respectively. These values are affected by interstitial cations. In meionite Me79.6, the average < T1-O > and < T2-O > distances are 1.647(1) and 1.670(1) angstrom, respectively, and they indicate that the occupancies are (Al(0.28)Si(0.72)) for T1 where the atoms are partially ordered and (Al(0.45)Si(0.55)) for T2 site where the atoms are nearly disordered, based on sodalite Si-O and Al-O distances of 1.6100(2) and 1.7435(2) angstrom, respectively.