Pressure-induced symmetry changes in body-centred cubic zeolites. Issue 7 (24th July 2019)

• Record Type: Journal Article
• Authors: Nearchou, Antony; Cornelius, Mero-Lee U.; Jones, Zöe L.; Collings, I. E.; Wells, Stephen A.; Raithby, Paul R.; Sartbaeva, Asel
• Is Part Of: Royal Society open science. Volume 6:Issue 7(2019)
• Publication Date: 2019-07-24
• Subjects: zeolite -- high pressure -- X-ray diffraction -- symmetry -- phase transition -- cubic; Science -- Periodicals; 500
• DOI: 10.1098/rsos.182158
• Languages: English
• ISSNs: 2054-5703

Abstract

Abstract : Previous work has shown a strong correlation between zeolite framework flexibility and the nature of structural symmetry and phase transitions. However, there is little experimental data regarding this relationship, in addition to how flexibility can be connected to the synthesis of these open-framework materials. This is of interest for the synthesis of novel zeolites, which require organic additives to permutate the resulting geometry and symmetry of the framework. Here, we have used high-pressure powder X-ray diffraction to study the three zeolites: Na-X, RHO and ZK-5, which can all be prepared using 18-crown-6 ether as an organic additive. We observe significant differences in how the occluded 18-crown-6 ether influences the framework flexibility—this being dependent on the geometry of the framework. We use these differences as an indicator to define the role of 18-crown-6 ether during zeolite crystallization. Furthermore, in conjunction with previous work, we predict that pressure-induced symmetry transitions are intrinsic to body-centred cubic zeolites. The high symmetry yields fewer degrees of freedom, meaning it is energetically favourable to lower the symmetry to facilitate further compression.