Crystal-fluid interaction and compressional behavior of chabazite with Li+, Na+, Ag+, K+, Rb+, and Cs+ as extra-framework cations

The high-pressure behavior of monovalent-cation-exchanged chabazites from Rubendorfel (Bohemia) (Ca1.6Na0.5Si8.4Al3.6O24·14.3H2O), in the form of Li+, Na+, Ag+, K+, Rb+, and Cs+ chabazite, was investigated by means of in situ synchrotron X-ray powder diffraction using pure water as penetrating pressure-transmitting fluid up to 5.5 GPa (at room temperature). The experiments were conducted: i) under hydrostatic consitions in the low-P range (< 1-5 GPa), and ii) under non-hydrostatic conditions in the higher P range (P > 1.5 GPa), in order to describe potential transformation phenomena even with sample compressed in solid H2O. In situ high-pressure synchrotron X-ray powder diffraction experiments on the as-prepared cation-forms of chabazites were performed at beamline 10-2 at the Stanford Synchrotron Radiation Light source (SSRL) at the SLAC National Accelerator Laboratory. At beamline 10-2, the synchrotron radiation from the wiggler insertion device impinges on a Si(111) crystal followed by two pinholes in order to create an approximately 200 micrometer diameter beam of monochromatic X-rays with a wavelength of 0.61992(5) Å. A Pilatus 300K-w Si-diode CMOS detector manufactured by DECTRIS was used to collect powder diffraction data. The detector held at distance of ca. 1032(2) mm from the sample was stepped to produce scattering angle coverage in 2- theta up to ca. 40°. A modified Merrill-Bassett diamond anvil cell (DAC), with two opposing diamonds supported by tungsten-carbide plates, was used for high-pressure XRD measurements. The pressure of a sample in the DAC was measured by detecting the shift in the R1 emission line of the included ruby chips (uncertancy: +/-0.05 GPa). Pressuredependent changes in the unit-cell lengths and volumes were derived from a series of whole profile fitting procedures using the EXPGUI suite of programs. Rietvel structure refinements are in progress. In all cases, except for Na-chabazite, a phase transition from the original rhombohedral to triclinic symmetry is observed in the range between 3.0 GPa and 5.0 GPa. The phase transition is accompanied by an abrupt decrease of the unit-cell volume by up to 10%. The apparent drasticaly different compressibility of the low-P rhombohedral forms suggests: i) P-induced penetration phenomena of H2O molecules, which lead to an anomalous stiffnes of the structure, ii) a drastic control of the extraframework population on the compressional behaviour and crystal-fluid interaction.