Temperature-dependent structural study of microporous CsAlSi5O12 |
| |
Authors: | Martin Fisch Boris Kolesov |
| |
Institution: | a Mineralogical Crystallography, Institute of Geological Sciences, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland b Institute of Inorganic Chemistry at the Russian Academy of Sciences, Novosibirsk, Russia |
| |
Abstract: | CsAlSi5O12 crystals were synthesized at high temperature by slow cooling of a vanadium oxide flux. Single-crystal X-ray diffraction structure analysis and electron microprobe analyses yielded the microporous CAS zeolite framework structure of Cs0.85Al0.85Si5.15O12 composition. High-temperature single-crystal and powder X-ray diffraction studies were utilized to analyze anisotropic thermal expansion. Rietveld refined cell constants from powder diffraction data, measured in steps of 25 °C up to 700 °C, show a significant decrease in expansion above 500 °C. At 500 °C, a displacive, static disorder-dynamic disorder-type phase transition from the acentric low-temperature space group Ama2 to centrosymmetric Amam (Cmcm in standard setting) was found. Thermal expansion below the phase transition is governed by rigid-body TO4 rotations accompanied by stretching of T-O-T angles. Above the phase transition at 500 °C all atoms, except one oxygen (O6), are fixed on mirror planes. Temperature-dependent polarized Raman single-crystal spectra between −270 and 300 °C and unpolarized spectra between room temperature and 1000 °C become increasingly less resolved with rising temperature confirming the disordered static-disordered dynamic type of the phase transition. |
| |
Keywords: | CsAlSi5O12 CAS zeolite framework structure Phase transition Temperature-dependent X-ray diffraction Raman spectroscopy |
本文献已被 ScienceDirect 等数据库收录! |
|