Data di Pubblicazione:
2003
Citazione:
Effects of pressure on the structure of bikitaite / P. Comodi, G.D. Gatta, P.F. Zanazzi. - In: EUROPEAN JOURNAL OF MINERALOGY. - ISSN 0935-1221. - 15:2(2003), pp. 247-255. [10.1127/0935-1221/2003/0015-0247]
Abstract:
The structural behaviour of bikitaite, Li2(Al2Si4O12). 2H2O, was investigated under hydrostatic pressure using X-ray single-crystal diffraction data. A Merrill-Bassett diamond anvil cell was mounted with glycerol, as non penetrating pressure-transmitting medium, ruby chips and a small crystal of quartz as the calibrant. A strong anisotropic compression was observed by linear regressions of lattice parameters against P, bikitaite being softer along the c axis (βc=9.3(1) 10-3 GPa-1), than along b (βb = 6.6(1) 10-3 GPa-1) and a (βa = 2.4(1) 10-3 GPa-1) (βa: βb: βc=1: 2.75 :3.9 . Fitting the cell-volume - pressure data to a second order Birch-Murnaghan equation of state, as indicated by the finite strain-stress plot, yielded K0 = 44.2(4) GPa, with K' = 4 and V0 = 295.58(2) Å3. The evolution of the bikitaite structure with P was studied by comparing the results of refinements with data collected at room conditions, at 3.2 GPa and after decompression. The structure can be described as sheets of six-membered rings parallel to (001), connected by pyroxene-like chains. 8-ring and 5-ring channels run along [010] and inside the 8-ring channel there is a onedimensional chain of water molecules, which is linked to the framework through the extra-framework Li atoms. Under pressure, the kinking of the pyroxene-like chain decreased the free diameters of the 5-ring channels, strongly reducing the distance between the ab planes. On the contrary, the tridymite-like planes with 6-membered rings were more rigid. The positions of the extra-framework cations and water were maintained at HP even though the configuration of the water chains changed slightly: the distances between the water molecules decreased, whereas the kinking angle of the chain increased.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
zeolite; bikitaite; single-crystal X-ray diffraction; high-pressure; compressibility
Elenco autori:
P. Comodi, G.D. Gatta, P.F. Zanazzi
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