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Download filePressure-Induced Hydration and Order−Disorder Transition in a Synthetic Potassium Gallosilicate Zeolite with Gismondine Topology
journal contribution
posted on 05.03.2008, 00:00 authored by Yongjae Lee, Sun Jin Kim, Chi-Chang Kao, Thomas VogtTwo high-pressure phases of a potassium gallosilicate with a gismondine framework (K−GaSi-GIS) were characterized using Rietveld refinements of in-situ high-pressure, high-resolution synchrotron
X-ray powder diffraction data. The observed response of the K−GaSi-GIS framework under hydrostatic
pressure is a gradual flattening of the so-called “double crankshaft” structural chain units. At pressures
below 1.0(1) GPa, additional water molecules from the hydrostatic pressure-transmitting medium are inserted
into the potassium-water guest network (“pressure-induced hydration”) resulting in a “super-hydrated” high-pressure phase I. As the flattening of the double crankshaft structural units in the GIS framework continues
above 1.6 GPa, the ellipticity of the cross-linking 8-ring windows is reduced below a certain threshold, and
a disordering of the potassium-water guest structure along the 8-ring channel, characteristic of a disordered
high-pressure phase II, is observed. The concerted framework distortion and guest network disordering
accommodates the increased hydration level while maintaining the seven-fold coordination environment of
the potassium cations to framework oxygen atoms and water molecules. We have thus established the
atomistic details of a guest−host order−disorder transition under pressure-induced hydration conditions in
a zeolite with GIS framework and compared it to other zeolites during pressure-induced hydration. We find
that the structural changes mediated by the extra-framework cations and their coordination environment
under PIH conditions are at the core of these different mechanisms and are driving the changes in the
ellipticity of pore openings, order−disorder and disorder−order transitions, and framework distortions.