STRUCTURAL EVOLUTION OF MICROPOROUS ZIRCONOSILICATE ELPIDITE UNDER HIGH PRESSURE
Yu. V. Seryotkin1,2, V. V. Bakakin3, I. V. Pekov4
1Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
3Nikolaev Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
4Lomonosov Moscow State University, Moscow, Russia
Keywords: zirconosilicate, elpidite, crystal structure, high pressure, phase transitions
Abstract
A high-pressure (up to 4.95 GPa) single-crystal XRD study is carried out of the natural zeolite-like hetero-framework zirconosilicate elpidite |Na1,65Ca0,15(H2O)3| [ZrSi6O15], sp. gr. Pbcm, a = 7.13201(19) Å, b = 14.6787(4) Å, c = 14.6297(3) Å, V = 1531.56(7) Å3, Z = 4. At pressures above 1.2 GPa, the elpidite undergoes a phase transition with the doubling of the a parameter of the unit cell (sp. gr. Pbca). The transition is caused by the opposite rotation of the originally equivalent Zr octahedra. Above 3.5 GPa, another phase transition is detected, this time with the symmetry being reduced to monoclinic (sp. gr. C1121/a). The framework deformation leads to a partial reorientation of H bonds in the extra-framework subsystem and a change in the configuration of Na and H2O chain from a unilaterally branched pattern to a bilaterally branched one.
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