Elastic behavior and pressure-induced structural modifications of the microporous Ca(VO)Si4O10·4H2O dimorphs cavansite and pentagonite
Articolo
Data di Pubblicazione:
2015
Abstract:
The behavior of natural microporous cavansite and pentagonite, orthorhombic dimorphs of Ca(VO) (Si4O10) ·4H2O, was studied at high pressure by in situ synchrotron x- ray powder diffraction with a diamond anvil cell using two different pressure- transmitting fluids: MeOH:EtOH:H2O = 16:3:1 (m.e.w.) and silicone oil (s.o.) . In situ diffraction- data on a cavansite sample were collected up to 8.17(5) GPa in (m.e.w) , and up to 7.28(5) GPa in (s.o) . The high- pressure structure evolution was studied from structural refinements at 1.08(5) , 3.27(5) and 6.45(5) GPa. The compressional behavior is strongly anisotropic. When the sample is compressed in s.o. from Pamb to 7.28(5) GPa, the vol. contraction is 12.2 %, whereas a, b and c decrease by 1.6 %, 10.3 % and 0.3 %, resp. The main deformation mechanisms at high- pressure are basically driven by variation of the T- O- T angles. Powder diffraction data on a pentagonite sample were collected up to 8.26(5) GPa in (m.e.w) and 8.35(5) GPa in (s.o) . Addnl. single- crystal x- ray diffraction expts. were performed in (m.e.w) up to 2.04(5) GPa. In both cases, pressure- induced over- hydration was obsd. in m.e.w. at high pressure. The penetration of a new H2O mol. leads to a stiffening effect of the whole structure. Also, between 2.45(5) and 2.96(5) GPa in (m.e.w) , a phase transition from an orthorhombic to a triclinic phase was obsd. In (s.o.) pentagonite also transformed to a triclinic phase >1.71(5) GPa. The overall compressibility of pentagonite and cavansite in (s.o.) is comparable, with a vol. contraction of 11.6 % and 12.2 %, resp. Crystallog. data and at. coordinates are given.
Tipologia CRIS:
03A-Articolo su Rivista
Keywords:
Heteropolyhedral frameworks, Cavansite, Pentagonite, Elastic behavior, Pressure-induced hydration
Elenco autori:
Rosa Micaela Danisi;Thomas Armbruster;Rossella Arletti;G. Diego Gatta;Giovanna Vezzalini;Simona Quartieri;Vladimir Dmitriev
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