Abstract
The structural transformations accompanying the thermal dehydration of natural elpidite, Na2ZrSi6O15 · 3H2O, have been studied by X-ray powder diffraction and IR spectroscopy. The crystal structures of both elpidite (a = 7.1136(1), b = 14.6764(2), c = 14.5977(2) A; sp. Gr. Pbcm) and the dehydration product Na2ZrSi6O15 (a = 14.0899(1), b = 14.4983(1), c = 14.3490(1)A; sp. gr. Cmce = Cmca) are based on a heteropolyhedral Si-Zr-O framework. The Na cations and (in hydrous elpidite) H2O molecules reside in extra-framework sites. The dehydration-induced distortion of the framework leads to a doubling of the a cell parameter, and the water loss is accompanied by a considerable decrease in molar volume.
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