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  • 1
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    Optical phonons, OH vibrations, and structural modifications of phlogopite at high temperatures: An in-situ infrared spectroscopic study (2016)
    Mineralogical Society of America
    Details
    Publication Date: 2016-08-03
    Description: The thermal behavior of optical phonons and OH vibrations of phlogopite (a trioctahedral mica) was examined at temperatures up to 1000 K using in situ infrared spectroscopy. The results showed that with increasing temperature, O–K bands in phlogopite exhibited a relatively strong variation in frequency in a manner similar to those in muscovite. The work revealed that different types of OH bands (fundamentals and combinations) have very different thermal behavior or temperature dependence, and their absorption coefficients are commonly not constant on heating. OH combination bands that are associated with summation processes of multi-phonon interactions commonly show a decrease in their intensities on heating, but in contrast combination bands due to difference processes generally exhibit an increase. This means that temperature dependencies of their absorption coefficients need to be considered when using the Beer-Lambert law to determine or estimate OH contents or hydrogen concentrations at high temperatures. The results showed a structural anomaly associated with a discontinuity in the temperature derivative of the wavenumber of Al–O and Si–O vibrations and O–H stretching near 600 K. However, framework-related phonon modes in the FIR and MIR regions do not suggest a break of the original monoclinic structural symmetry in the investigated temperature region. The complex changes are attributed to temperature-induced alteration of local configuration involving TO 4 tetrahedra and a possible change of the orientation of OH dipoles, in addition to a previously reported distortion of MO 6 octahedra. Increasing temperature to 1000 K also causes partial dehydroxylation, as evidenced by the disappearance of the OH band near 3623 cm –1 and the decrease in OH band height and area of other OH bands. The study did not record the formation of H 2 O inside phlogopite as a result of partial dehydroxylation. The work offers new data and findings that have important implications in understanding the complex structural modifications and the behavior of phonon modes and the thermal stability of hydroxyls on approaching the dehydroxylation, as well as the way hydrogen is released from micas at high temperatures. Our data also show that phologpite becomes less transparent with increasing temperature suggesting a change of radiative properties and ability to transmit heat, which could be of interest for modeling thermal-transmission in crustal rocks.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 2
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    The nature of the 660-kilometer discontinuity in Earth's mantle from global seismic observations of PP precursors (2006)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2006-01-18
    Description: The 660-kilometer discontinuity, which separates Earth's upper and lower mantle, has been detected routinely on a global scale in underside reflections of precursors to SS shear waves. Here, we report observations of this discontinuity in many different regions, using precursors to compressional PP waves. The apparent absence of such precursors in previous studies had posed major problems for models of mantle composition. We find a complicated structure, showing single and double reflections ranging in depth from 640 to 720 kilometers, that requires the existence of multiple phase transitions at the base of the transition zone. The results are consistent with a pyrolite mantle composition.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Deuss, Arwen -- Redfern, Simon A T -- Chambers, Kit -- Woodhouse, John H -- New York, N.Y. -- Science. 2006 Jan 13;311(5758):198-201.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Earth Sciences, University of Cambridge, Cambridge CB3 0EZ, UK. deuss@esc.cam.ac.uk〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16410518" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 3
    Electronic Resource
    Electronic Resource
    Structures of synthetic K2MgSi5O12 leucites by integrated X-ray powder diffraction, electron diffraction and 29Si MAS NMR methods (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 31-41 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768193008754
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  • 4
    Electronic Resource
    Electronic Resource
    Structural relations and tetrahedral ordering pattern of synthetic orthorhombic Cs2CdSi5O12 leucite: a combined synchrotron X-ray powder diffraction and multinuclear MAS NMR study (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 50 (1994), S. 560-566 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768194003393
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  • 5
    Electronic Resource
    Electronic Resource
    UNITCELL: a nonlinear least-squares program for cell-parameter refinement and implementing regression and deletion diagnostics (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 30 (1997), S. 84-84 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889896011673
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  • 6
    Electronic Resource
    Electronic Resource
    Distortion Characteristics Across the Structural Phase Transition in (Cu1−xZnx)WO4 (1997)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 53 (1997), S. 102-112 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Rietveld analysis of neutron powder diffraction data on the sanmartinite (ZnWO4)-cuproscheelite (CuWO4) solid solution has enabled the comparison of microscopic and macroscopic order parameters associated with the P2/c–P\overline 1 structural phase transition. The macroscopic spontaneous strain, calculated from the lattice parameters, conforms well with a second-order Landau model. Furthermore, this is also true of the symmetry-related atomistic M—O order parameter and the quadratic elongation of the MO6 octahedra. It is clear that the Jahn–Teller effect, associated with the divalent Cu cation, is the driving force for the phase transition and the excess elongation evident in the M—O(2) bond giving rise to the non-symmetry predicted strain element e22. The existence of a large region of order parameter saturation at the copper-rich end of the solid solution is also associated with the MO6 elongation and the breakdown of the homogeneous strain field of the zinc solute atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108768196010403
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  • 7
    Electronic Resource
    Electronic Resource
    Determination of olivine cooling rates from metal-cation ordering (1996)
    [s.l.] : Nature Publishing Group
    Nature 381 (1996), S. 407-409 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] It has been recognized for some time that non-equilibrium cation ordering in minerals might provide a means to measure rock cooling rates, from early work on Mg/Fe ordering in amphi-boles6 and extensive studies of pyroxenes7'8 to more recent analysis of Al/Si ordering in alkali feldspars9. ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/381407a0
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  • 8
    Electronic Resource
    Electronic Resource
    Spontaneous strain below the $$I\bar 1 - P\bar 1$$ transition in anorthite at pressure (1989)
    Springer
    Physics and chemistry of minerals 16 (1989), S. 539-544 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The phase transition between the $$P\bar 1$$ and $$I\bar 1$$ phases of anorthite has been studied at elevated pressure by single-crystal X-ray diffraction in a diamond-anvil cell. The phase transition is shown to be first-order in character for both end-member anorthite (CaAl2Si2O8) and for an anorthite with a small amount of albite component (NaAlSi3O8) in solid solution. Reversals of the transition across the phase boundary at three other compositions show that the transition pressure (P Tr) increases with increasing albite content. This behaviour is compared with that observed at elevated temperatures, and is analysed in terms of Landau theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202208
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  • 9
    Electronic Resource
    Electronic Resource
    Kinetics of dehydration of Ca-montmorillonite (1999)
    Springer
    Physics and chemistry of minerals 26 (1999), S. 591-600 
    Details
    ISSN: 1432-2021
    Keywords: Key words Montmorillonite ; Fuller's earth ; Dehydration ; Kinetics ; Thermogravimetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Isothermal thermogravimetric experiments have been carried out to determine the reaction kinetics of the dehydration processes in fuller's earth, a natural Ca-montmorillonite. Dehydration in swelling clays is a complex reaction, and analysis of the thermogravimetric data using empirical rate equations and time-transformation analysis reveals that the nature of the rate controlling mechanism is dependent upon both the temperature regime of the sample as well as the extent of reaction. For fuller's earth, we find that the dehydration kinetics are dominated by a nucleation and growth mechanism at low temperatures and fractions transformed (stage I), but above 90 °C the last stages of the reaction are diffusion controlled (stage II). The activation energy for dehydration during stage I is around 35 kJ · mol−1, whereas the removal of water during stage II requires an activation energy of around 50 kJ · mol−1. These two stages of dehydration are associated with primary collapse of the interlayer (stage I) and movement of water that is hydrated to cations within the interlayer (stage II).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050223
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  • 10
    Electronic Resource
    Electronic Resource
    Cu 2p absorption spectroscopy as a probe for the site occupancy of (ZnxCu1−x)WO4 solid solution (1993)
    Springer
    Physics and chemistry of minerals 20 (1993), S. 375-381 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The solid solution sanmartinite (ZnWO4)—cuproscheelite (CuWO4) has been studied using Cu 2p X-ray absorption spectroscopy. While a single L3 absorption peak is observed for CuWO4, two distinct L3 absorption peaks with a separation of ∼0.8 eV are observed for the intermediate samples in the solid solution. The two peaks represent distinct Cu sites: one with all CuO6 next nearest neighbours in the (Cu,Zn)O6 chains, another having at least one ZnO6 next nearest neighbour. Both sites show a linear increase in covalency as a function of increasing Cu-content. The relative intensities of the two absorption peaks is dependent upon the Cu-content and has been used to model the site occupancies. The results reveal that the local structural effects can be associated with a composition-dependent structural phase transition from P2/c (ZnWO4) to P $$\bar 1$$ (CuWO4). Deviations from a single-site model are explained in terms of the local environments, and evidence for site preferences and local clustering are explored.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203106
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