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Behavior of 10-Å phase at low temperatures

Title data

Zanazzi, P. F. ; Comodi, Paola ; Nazzareni, S. ; Rotiroti, Nicola ; van Smaalen, Sander:
Behavior of 10-Å phase at low temperatures.
In: Physics and Chemistry of Minerals. Vol. 34 (2006) Issue 1 . - pp. 23-29.
ISSN 1432-2021
DOI: https://doi.org/10.1007/s00269-006-0123-9

Abstract in another language

The thermal evolution of 10-Å phase Mg₃Si₄O10(OH)₂ ·H₂O, a phyllosilicate which may have an important role in the storage/release of water in subducting slabs, was studied by X-ray single-crystal diffraction in the temperature range 116--293 K. The lattice parameters were measured at several intervals both on cooling and heating. The structural model was refined with intensity data collected at 116 K and compared to the model refined at room temperature. As expected for a layer silicate on cooling in this temperature range, the a and b lattice parameters undergo a small linear decrease, α a = 1.7(4) 10⁻⁶ K⁻¹ and α b = 1.9(4) 10⁻⁶ K⁻¹, where α is the linear thermal expansion coefficient. The greater variation is along the c axis and can be modeled with the second order polynomial c T = c₂₉₃(1 + 6.7(4)10⁻⁵ K⁻¹ΔT + 9.5(2.5)10⁻⁸ K⁻²ΔT)²) where ΔT = T − 293 K; the monoclinic angle β slightly increased. The cell volume thermal expansion can be modeled with the polynomial V T = V₂₉₃ (1 + 8.0 10⁻⁵ K⁻¹ ΔT + 1.4 10⁻⁷ K⁻² (ΔT)²) where ΔT = T − 293 is in K and V in ų. These variations were similar to those expected for a pressure increase, indicating that T and P effects are approximately inverse. The least-squares refinement with intensity data measured at 116 K shows that the volume of the SiO₄ tetrahedra does not change significantly, whereas the volume of the Mg octahedra slightly decreases. To adjust for the increased misfit between the tetrahedral and octahedral sheets, the tetrahedral rotation angle α changes from 0.58° to 1.38°, increasing the ditrigonalization of the silicate sheet. This deformation has implications on the H-bonds between the water molecule and the basal oxygen atoms. Furthermore, the highly anisotropic thermal ellipsoid of the H₂O oxygen indicates positional disorder, similar to the disorder observed at room temperature. The low-temperature results support the hypothesis that the disorder is static. It can be modeled with a splitting of the interlayer oxygen site with a statistical distribution of the H₂O molecules into two positions, 0.6 Å apart. The resulting shortest Obas--OW distances are 2.97 Å, with a significant shortening with respect to the value at room temperature. The low-temperature behavior of the H-bond system is consistent with that hypothesized at high pressure on the basis of the Raman spectra evolution with P.

Further data

Item Type: Article in a journal
Refereed: Yes
Institutions of the University: Faculties > Faculty of Mathematics, Physics und Computer Science > Group Material Sciences > Chair Crystallography > Chair Crystallography - Univ.-Prof. Dr. Sander van Smaalen
Faculties
Faculties > Faculty of Mathematics, Physics und Computer Science
Faculties > Faculty of Mathematics, Physics und Computer Science > Group Material Sciences
Faculties > Faculty of Mathematics, Physics und Computer Science > Group Material Sciences > Chair Crystallography
Result of work at the UBT: Yes
DDC Subjects: 500 Science > 530 Physics
Date Deposited: 26 Feb 2016 07:41
Last Modified: 24 Oct 2017 13:42
URI: https://eref.uni-bayreuth.de/id/eprint/31189