Dehydration dynamics of bikitaite: I. In situ synchrotron X-ray powder diffraction study

High-temperature behavior and the process of thermal dehydration in the natural zeolite bikitaitehave been studied by ab initio molecular dynamics simulations, and favorably compared with the X-raypowder diffraction data presented in Part I of this work (Ferro et al. 2003). The microscopic dynamicalbehavior of the extraframework species (water molecules and Li cations) has been characterized as afunction of temperature. Two regimes have been detected, and the transition is characterized by thebreaking of the one-dimensional water chain typical of bikitaite at room temperature. The elementarysteps for the diffusion of water inside the bikitaite channels have been studied by means of a rareevents-sampling technique (Bluemoon Ensemble). The activation free-energy for a site-to-site waterjump has been calculated and a mechanism for the dehydration process is proposed.