caa a22 4500 463217012 CHVBK 20180405153200.0 cr unu---uuuuu 170326e20070101xx s 000 0 eng 10.1007/s00269-006-0123-9 doi (NATIONALLICENCE)springer-10.1007/s00269-006-0123-9 Behavior of 10-Å phase at low temperatures [Elektronische Daten] [P. Zanazzi, P. Comodi, S. Nazzareni, N. Rotiroti, S. van Smaalen] 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 116-293K. The lattice parameters were measured at several intervals both on cooling and heating. The structural model was refined with intensity data collected at 116K 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) 10−6K−1 and α b =1.9(4) 10−6K−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 =c 293(1+6.7(4)10−5K−1ΔT+9.5(2.5)10−8K−2(ΔT)2) where ΔT=T−293K; the monoclinic angle β slightly increased. The cell volume thermal expansion can be modeled with the polynomial V T =V 293 (1+8.0 10−5K−1 ΔT+1.4 10−7K−2 (ΔT)2) where ΔT=T−293 is in K and V in Å3. 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 116K 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, 0.6Å apart. The resulting shortest Obas-OW distances are 2.97Å, 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. Springer-Verlag, 2006 10-Å phase nationallicence Thermal expansion nationallicence Low-temperature nationallicence Zanazzi P. Dipartimento di Scienze della Terra, Università di Perugia, Piazza dell'Università, 06100, Perugia, Italia aut Comodi P. Dipartimento di Scienze della Terra, Università di Perugia, Piazza dell'Università, 06100, Perugia, Italia aut Nazzareni S. Dipartimento di Scienze della Terra, Università di Perugia, Piazza dell'Università, 06100, Perugia, Italia aut Rotiroti N. Dipartimento di Scienze della Terra, Università di Milano, Milano, Italy aut van Smaalen S. Laboratory of Crystallography, University of Bayreuth, Bayreuth, Germany aut Physics and Chemistry of Minerals Springer-Verlag 34/1(2007-01-01), 23-29 0342-1791 34:1<23 2007 34 269 https://doi.org/10.1007/s00269-006-0123-9 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s00269-006-0123-9 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Zanazzi P. Dipartimento di Scienze della Terra, Università di Perugia, Piazza dell'Università, 06100, Perugia, Italia aut NATIONALLICENCE 700 1- Comodi P. Dipartimento di Scienze della Terra, Università di Perugia, Piazza dell'Università, 06100, Perugia, Italia aut NATIONALLICENCE 700 1- Nazzareni S. Dipartimento di Scienze della Terra, Università di Perugia, Piazza dell'Università, 06100, Perugia, Italia aut NATIONALLICENCE 700 1- Rotiroti N. Dipartimento di Scienze della Terra, Università di Milano, Milano, Italy aut NATIONALLICENCE 700 1- van Smaalen S. Laboratory of Crystallography, University of Bayreuth, Bayreuth, Germany aut NATIONALLICENCE 773 0- Physics and Chemistry of Minerals Springer-Verlag 34/1(2007-01-01), 23-29 0342-1791 34:1<23 2007 34 269 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer