On the high-pressure behavior of gobbinsite, the natural counterpart of the synthetic zeolite Na–P2

Abstract

An in situ high-pressure single-crystal X-ray diffraction study of gobbinsite, the natural counterpart of the synthetic zeolite Na–P2, was carried out up to 4.3GPa. No evidence of amorphization was observed within pressure-range investigated. Using a non-penetrating P-medium, two changes of the elastic behavior occur: the first at 1.1–1.3GPa and the second at 2.7–3.2GPa. Birch-Murnaghan equations of state truncated to the second order were used to fit the experimental P–V data within the three P-ranges (i.e. 0.0001–1.1, 1.3–2.7 and 3.2–4.3GPa), giving the following isothermal bulk moduli (KV0): 46.3(9), 52(8) and 28(6) GPa, respectively. The unit-cell compression is significantly anisotropic. In response to the applied pressure, the 8-membered ring channel parallel to [100] undergoes a significant increase of ellipticity, whereas the channel parallel to [010] undergoes a shrinking towards a circular shape at P≥1.3GPa. A partial re-organization of the H2O sites occurs between 1.1 and 1.3GPa, and new framework deformational modes onset at P≥3.2GPa, coupled with a change in the coordination environment of the extraframework cations.