High-pressure behavior and crystal-fluid interaction in natural erionite-K

The high-pressure behavior of a natural erionite-K has been investigated by in situ single-crystal synchrotron X-ray diffraction with a diamond anvil cell (DAC), using four different P-transmitting fluids: the non-penetrating silicone oil and the potentially penetrating methanol:ethanol:H2O = 16:3:1 mixture, pure H2O and naturally hydrated glycerol. The investigated crystals showed typical offretite stacking faults in the diffraction pattern. The experiment in silicone oil showed that the erionite bulk compressibility lies within the range observed for the previously investigated zeolites, as its refined bulk modulus (KV0 = 1/βV0), calculated within the range Pamb-1.52(5) GPa, resulted equal to 47(2) GPa. The high-pressure experiments performed using potentially penetrating P-transmitting fluids showed significantly lower compressibilities, unambiguously suggesting the P-mediated intrusion of new molecules into the structural voids. Further evidence is provided by the comparative analysis of the framework deformation mechanisms: erionite-K compressed in m.e.w. showed a drastically lower compressibility of the erionite cage, with respect to silicone oil. In conclusion, this study suggests natural erionite, a relatively common zeolite, as a suitable candidate for the P-mediated intrusion and hyper-confinement of molecules into the framework microcavities.