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Elastic behavior, phase transition, and pressure induced structural evolution of analcime
No full textElastic and structural behavior of a natural cubic analcime (space group: Ia(3) over bard) from Sardinia (Italy) was investigated at high pressure by in situ single-crystal X-ray diffraction. A first-order phase transition is observed in the pressure range between 0.91(5) and 1.08(5) GPa. Unit-cell constants and reflection conditions confirm that the space group of the HP-polymorph is P(1) over bar. No further phase-transition has been observed at least up to 7.14 GPa. Fitting the volume data of the cubic polymorph with a second-order BM-EoS we obtain: V-0 = 2571.2(4) angstrom(3), K-T0 = 56(3) GPa, and K = 4 (fixed). For the triclinic polymorph, a third-order EoS gives: V-0 = 2607(9) angstrom(3), K-T0 = 19(2) GPa, and K' = 6.8(7). Axial bulk moduli of the triclinic polymorph, calculated with a linearized BM-EoS, are: K-T0(a) = 29(2) GPa, with K'(a) = 4.9(6) and a(0) = 13.727(10) angstrom; K-T0(b) = 20(1) GPa, with K'(b) = 5.2(5), and b(0) = 13.751(15) angstrom; K-T0(c) = 11(1) GPa, with K'(c) = 12.6(6) and c(0) = 13.822(31) angstrom. The elastic behavior of the HP-polymorph appears to be strongly anisotropic, being K-T0(a):K-T0(b):K-T0(c) = 2.64:1.82:1.00. The relevant structural variations in response to the cubic --> triclinic phase transition are due to tetrahedral tilting. The tetrahedral framework distortion gives rise to a change of the eight- and six-ring channels ellipticity and of the extra-framework topological configuration: it appears in fact that for the high-pressure triclinic polymorph the coordination number of some of the Na atoms is seven (2H(2)O + five framework O atoms) instead of six (2H(2)O + four framework O atoms)
The effect of Ca substitution on the elastic and structure behaviour of orthoenstatite (Mg2Si2O6) up to 10.2 GP
No full textAbstract 3.3.a
The effect of Ca substitution on the compressional behavior of enstatite (Mg2Si2O6) up to 10 GPa
No full textAbstract n° A25
Behaviour at high pressure of Rb7NaGa8Si12O40·3H2O (a zeolite with EDI topology): a combined experimental–computational study
No full textThe high-pressure behaviour and the P-induced structural evolution of a synthetic zeolite Rb7NaGa8Si12O40·3H2O (with edingtonite-type structure) were investigated both by in situ synchrotron powder diffraction (with a diamond anvil cell and the methanol:ethanol:water = 16:3:1 mixture as pressure-transmitting fluid) up to 3.27 GPa and by ab initio first-principles computational modelling. No evidence of phase transition or penetration of P-fluid molecules was observed within the P-range investigated. The isothermal equation of state was determined; V0 and KT0 refined with a second-order Birch–Murnaghan equation of state are V0 = 1311.3(2) Å3 and KT0 = 29.8(7) GPa. The main deformation mechanism (at the atomic scale) in response to the applied pressure is represented by the cooperative rotation of the secondary building units (SBU) about their chain axis (i.e. [001]). The direct consequence of SBU anti-rotation on the zeolitic channels parallel to [001] is the increase in pore ellipticity with pressure, in response to the extension of the major axis and to the contraction of the minor axis of the elliptical channel parallel to [001]. The effect of the applied pressure on the bonding configuration of the extra-framework content is only secondary. A comparison between the P-induced main deformation mechanisms observed in Rb7NaGa8Si12O40·3H2O and those previously found in natural fibrous zeolites is made
Compressional behaviour and P-induced structural evolution of topaz, Al2SiO4(F,OH)2
No full textAbstract 3.4.b
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