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  • 1
    Electronic Resource
    Electronic Resource
    Vibrational spectra of Mg(OH)2 and Ca(OH)2 under pressure (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 5910-5915 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effects of compression on the structure and bonding of Mg(OH)2 brucite and Ca(OH)2 portlandite are documented to pressures of 34 and 24 GPa, respectively, by way of infrared spectroscopy of the O–H stretching vibration at 300 K. The frequency of the infrared-active (A2u) mode of both hydroxides decreases with pressure, by −0.6 cm−1/GPa for Mg(OH)2 over the pressure range studied, and by −3.5 cm−1/GPa for Ca(OH)2 to 10.6 GPa. An additional mode observed in Mg(OH)2 is due to an optically induced hot band (A2u X A2u overtone): with increasing pressure, its intensity grows and its frequency decreases (−3.7 cm−1/GPa). The negative pressure dependencies of these modes (negative Grüneisen parameters) are explained in terms of compression increasing the hydrogen bond strength within the hydroxide structure. On increasing pressure above 12.8 GPa, the full width at half-maximum of the O–H vibration in Ca(OH)2 rapidly broadens by a factor of 4. The infrared data suggest that Ca(OH)2 undergoes pressure-induced amorphization at 11.7(±1.1) GPa at 300 K, consistent with independently collected x-ray diffraction patterns. In the amorphous phase, a distribution of O–O bond lengths ranging between 2.8 and 3.3 A(ring) is inferred from the breadth of the vibrational band. On decompression, the infrared spectra show a full return to the crystalline form at 2.8 (±1.4) GPa. Neither upon amorphization with increasing pressure nor upon recrystallization with decreasing pressure are there any prescursory phenomena evident in the spectra. In contrast with Ca(OH)2, the isomorphous Mg(OH)2 appears to be stable throughout the pressure range of this study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457460
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  • 2
    Electronic Resource
    Electronic Resource
    Compositional controls on the partitioning of U, Th, Ba, Pb, Sr and Zr between clinopyroxene and haplobasaltic melts: implications for uranium series disequilibria in basalts
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 128 (1994), S. 407-423 
    Details
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0012-821X(94)90159-7
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  • 3
    Electronic Resource
    Electronic Resource
    Fast rise times and the physical mechanism of deep earthquakes (1991)
    [s.l.] : Nature Publishing Group
    Nature 352 (1991), S. 520-522 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The notion that phase transformations may explain the existence of deep earthquakes is nearly half a century old14, but has recently gained support from laboratory experiments. The observation of high-pressure shear failure in ice and Mg2GeO4 undergoing metastable phase transitions4"6 led to the ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/352520a0
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  • 4
    Electronic Resource
    Electronic Resource
    An infrared spectroscopic study of lawsonite to 20 GPa (1999)
    Springer
    Physics and chemistry of minerals 26 (1999), S. 437-445 
    Details
    ISSN: 1432-2021
    Keywords: Key words lawsonite ; high pressure ; infrared spectroscopy ; hydrogen bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The infrared spectrum of CaAl2Si2O7 · H2O-lawsonite, has been characterized to pressures of 20 GPa at 300 K. Our results constrain the response to compression of the silicate tetrahedra, hydroxyl units, and water molecules in this material. The asymmetric and symmetric stretching and bending vibrations of the Si2O7 groups (at zero pressure frequencies between 600 and 1000 cm−1) increase in frequency with pressure at rates between 3.6 and 5.9 cm−1/GPa. All silicate modes appear to shift continuously with pressure to 20 GPa, although the lowest frequency stretching vibration becomes unresolvable above 18 GPa, and a splitting of the main bending vibration is observed near this pressure. The O-H stretches of the hydroxyl units exhibit a discontinuity in their mode shifts at ∼8–9 GPa, which we interpret to be produced by a pressure-induced change in hydrogen bonding. The stretching and bending vibrations of the water molecule are relatively unaffected by compression to 20 GPa, thus demonstrating that the structural cavities in which water molecules reside are relatively rigid. Significant changes in the amplitude of the O-H stretches of the hydroxyl and water units are observed at this pressure as well; nevertheless, our results demonstrate that the dominant structural units in lawsonite persist metastably at 300 K with only modest structural modifications well beyond the known stability field of this phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050206
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  • 5
    Electronic Resource
    Electronic Resource
    A theory of cross-sectional shrinkage distortion and its experimental verification (1992)
    Springer
    Wood science and technology 26 (1992), S. 353-368 
    Details
    ISSN: 1432-5225
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Summary A theory has been developed for calculating the cup and edge distortion that will occur when green boards are dried, or the moisture content of dry boards changes in service. The parameters on which the calculations are based are the annual ring orientation coordinates R and θ of the boards, and the transverse shrinkage factors. For boards of square-cross-section the theory agrees very closely with the shrinkage predicted by the older theory of Greenhill, MacLean and Keylwerth. For Beilschmiedia tawa specimens 50×50 mm in cross-section the experimental and calculated width and thickness shrinkage were in excellent agreement. For radiata pine boards 200×50 mm in cross-section the experimental cup, edge distortion and shrinkage in width and thickness agreed very closely with the values predicted by the theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00226077
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  • 6
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    Fast intracavity polarization dynamics of an erbium-doped fiber ring laser: Inclusion of stochastic effects (1997)
    American Physical Society
    Details
    Publication Date: 1997-03-01
    Print ISSN: 1050-2947
    Electronic ISSN: 1094-1622
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Published by American Physical Society
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  • 7
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    Equivalence of the Boson Peak in Glasses to the Transverse Acoustic van Hove Singularity in Crystals (2011)
    American Physical Society
    Details
    Publication Date: 2011-05-31
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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  • 8
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    A Cr 3+ luminescence study of natural topaz Al 2 SiO 4 (F,OH) 2 up to 60 GPa (2019)
    Mineralogical Society of America
    Details
    Publication Date: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉Topaz [Al〈sub〉2〈/sub〉SiO〈sub〉4〈/sub〉(F,OH)〈sub〉2〈/sub〉] is a subduction-related mineral that is found in metasediments and has a large pressure and temperature stability field. Here, we use luminescence spectroscopy of Cr〈sup〉3+〈/sup〉 to probe the Al site in topaz at pressures up to ~60 GPa, which corresponds to a depth of ~1400 km in the Earth. This technique allows us to probe all three unique Al environments (i.e., [AlO〈sub〉4〈/sub〉(OH)〈sub〉2〈/sub〉]〈sup〉7–〈/sup〉, [AlO〈sub〉4〈/sub〉(F)〈sub〉2〈/sub〉]〈sup〉7–〈/sup〉, and [AlO〈sub〉4〈/sub〉OH,F]〈sup〉7–〈/sup〉) simultaneously under high pressure. We find that the R-line luminescence from all three Al environments shift linearly to longer wavelength to ~40 GPa. Above ~40 GPa, they shift nonlinearly and begin to flatten out at ~48 GPa, with a pressure shift of ~0 cm〈sup〉–1〈/sup〉/GPa from ~48–55 GPa. Our results, combined with previous high-pressure single-crystal X-ray diffraction studies to ~45 GPa, strongly indicate that there is a change in the compression mechanism in topaz above ~40 GPa. Our high-pressure room-temperature results show that the metastable persistence of topaz on compression represents one of the most extreme cases among tetrahedrally coordinated silicates.〈/span〉
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences , Physics
    Published by Mineralogical Society of America
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  • 9
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    A Cr3+ luminescence study of spodumene at high pressures: Effects of site geometry, a phase transition, and a level-crossing (2016)
    Mineralogical Society of America
    Details
    Publication Date: 2016-06-03
    Description: Cr 3+ luminescence of the green Cr-bearing variety of spodumene (LiAlSi 2 O 6 ) has been studied under hydrostatic conditions up to ~15 GPa. R-line luminescence is a particularly sensitive site-specific probe of the Al-site, and high-pressure phase transitions that affect the symmetry or electron density at this site should produce obvious changes in the luminescence spectra. Thus, the nature of Cr 3+ luminescence is probed across known and possible phase transitions in spodumene. Discontinuous shifts of the R-lines and their sidebands to higher energy at 3.2 GPa are associated with the C 2/ c to P 2 1 / c phase transition. Both R-lines and sidebands shift to lower energy after the 3.2 GPa transition up to ~15 GPa. The C 2/ c to P 2 1 / c phase transition is confirmed to be first order in nature based on its observed hysteresis on decompression, and R-line and sideband measurements give no evidence of a second proposed transition up to ~15 GPa. The splitting between the R 1 and R 2 bands is dramatically enhanced by pressure, with the split decreasing at the phase transition. These trends correspond to pressure-induced shifts in the distortion of the M1 site, and a likely shift in off-centeredness of the Cr 3+ ion. Pressure-induced decreases in line widths are consistent with the R-lines shifting at slower rates than the phonons to which they are most closely coupled, as demonstrated by large pressure shifts of vibronic peaks. Observations of a pressure-induced cross-over between the 4 T 2 and 2 E levels of the Cr 3+ ion indicate that spodumene undergoes a shift from an intermediate strength crystal field environment to a high strength crystal field environment at pressures between ambient and 3.2 GPa.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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  • 10
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    A high-temperature Brillouin scattering study on four compositions of haplogranitic glasses and melts: High-frequency elastic behavior through the glass transition (2013)
    Mineralogical Society of America
    Details
    Publication Date: 2013-02-13
    Description: The sound velocities ( nv p , v p , v s ) and refractive index n of four haplogranitic glasses and melts have been measured as a function of temperature by Brillouin scattering spectroscopy. The measurements were conducted at GHz frequency, through the glass transition temperature ( T g ), using both platelet and backscattering geometries. The compositions of the four haplogranites are based on the addition of ~5 wt% each of the components Li 2 O, F 2 O –1 , Na 2 O, and K 2 O to a haplogranitic (HPG8) composition. Marked changes in slope and sign are observed in the temperature dependences of sound velocities ( nv p , v p , v s ) as a function of composition. The glass transition temperatures T g of the haplogranite samples are determined from distinct slope changes of sound velocities ( v p and v s ) vs. temperature. The lithium-enriched glass has the lowest glass transition temperature (466 °C), while the potassic glass has the highest glass transition temperature (575 °C). The unrelaxed bulk moduli vary markedly with composition below the glass transition, as do their temperature dependencies: the bulk moduli of the F- and Na-rich glasses have positive shifts with temperature. For comparison, the shear moduli have relatively similar temperature dependences below T g for different alkali contents. At temperatures above the glass transition, the temperature derivatives of the bulk moduli, which for these frequencies reflect the vibrational compressibilities of the liquids, shift to more negative values. However, the compositional range over which the bulk moduli undergo positive or small negative temperature shifts of the vibrational compressibility appears to extend to NBO/T ratios near 0.3–0.4, or spanning most haplogranite compositions.
    Print ISSN: 0003-004X
    Electronic ISSN: 1945-3027
    Topics: Geosciences
    Published by Mineralogical Society of America
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