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  • 1
    Electronic Resource
    Electronic Resource
    Instrumentation and key elements of the dispersive x-ray absorption spectrometer for accurate measurements (invited) (abstract) : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1616-1616 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Measurement of very small differences of the total cross section is the current demand for the spectrometers dedicated to time-dependent experiments carried out under various time-ramped parameters. The dispersive optics and more precisely the full x-ray-absorption spectrometer is mechanically movement-free during data collection which can last over 12 h at LURE-DCI to be sensitive to relative change of the absorption of the order of 10−5. In this range, artefacts due to the drift of silicon lattice spacing under temperature change of the crystal, and drifts of the detector position because of liquid–nitrogen evaporation contained in the cryostat, are sources of errors which have been identified and cured or ... by-passed. The accuracy in difference measurements is now of the order of 10−5 for a total cross section measured equal to 1. In term of optics stability a difference signal of 10−4 out of 1 can be generated by an absorption edge shift caused by a 0.05 K drift of the temperature of the silicon crystal at 7 keV. These performances are essential for the measurement of XMCD in the hard-x-ray range. Water cooling of the dynamically bent crystal reduces dramatically the change of the Si temperature. Adequate geometry makes the spatial drift of the position of the photodiode array much less concerning. The focusing efficiency is also a key parameter to push high-pressure x-ray-absorption spectroscopy (55 GPa), and high-temperature XAS (2000 K), and the combination (15 GPa, 800 K). Simple devices, taking advantage of the focusing geometry, have been successfully tested these last two years. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145859
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  • 2
    Electronic Resource
    Electronic Resource
    Powder X-ray diffraction under extreme conditions of pressure and temperature (1999)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 6 (1999), S. 81-86 
    Details
    ISSN: 1600-5775
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An important work has been carried out in the field of X-ray diffraction in obtaining accurate structural information from materials at extreme conditions of pressure and temperature. An experimental set-up combining a diamond-anvil high-pressure cell and a laser-heating technique has been installed at the high-pressure beamline ID30 at the ESRF (Grenoble) to study two major constituents of the Earth's deep interior: MgSiO3 perovskite and iron. Experiments carried out on MgSiO3 perovskite up to 86 GPa and over 2000 K yielded detailed structural information on this compound under these conditions and thus important constraints for the lower mantle mineralogical model, favouring a mixture of perovskite and magnesiowüstite. X-ray diffraction patterns recorded on imaging plates with micro-focused monochromatic radiation revealed a new high-temperature structure of iron above 40 GPa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S090904959900028X
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  • 3
    Electronic Resource
    Electronic Resource
    High-pressure behaviour of germanate olivines studied by X-ray diffraction and X-ray absorption spectroscopy (1996)
    Springer
    Physics and chemistry of minerals 23 (1996), S. 173-185 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Germanate olivines Mg2GeO4, Ca2GeO4 and CaMgGeO4 have been studied by high-pressure X-ray Diffraction and high-pressure X-ray Absorption Spectroscopy. The three compounds were compressed, in the 0–30 GPa pressure range, at room temperature in a diamond-anvil cell, silicon oil being used as the pressure transmitting medium. Values of K0 are 166 ± 15, 117 ± 15 and 152 ± 14 GPa for Mg2GeO4, Ca2GeO4 and CaMgGeO4 respectively. These olivines all exhibit compression anisotropy, the a axis being the least compressible. Crystal to crystal phase transitions have been observed in Mg2GeO4 and Ca2GeO4 above 12 GPa and 6 Gpa respectively. The nature of these structural changes remains unclear yet. The onset of amorphization has been observed in Mg2GeO4 and Ca2GeO4 at pressures above about 22 and 11 GPa respectively. These phase transitions and amorphization processes do not involve any detectable increase in the coordination number of germanium atoms. At higher pressure (P 〉23 GPa), we report the onset of a transition from a phase with fourfold coordinated germanium to a phase with higher germanium coordination number in CaMgGeO4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00220728
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  • 4
    Electronic Resource
    Electronic Resource
    P-V-T equation of state of lawsonite (1999)
    Springer
    Physics and chemistry of minerals 26 (1999), S. 406-414 
    Details
    ISSN: 1432-2021
    Keywords: Key words Lawsonite ; Equation of state ; X-ray diffraction ; High-pressure ; High-temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  A pressure-volume-temperature data set has been obtained for lawsonite [CaAl2Si2O7(OH)2.H2O], using synchrotron X-ray diffraction and an externally heated diamond anvil cell. Unit-cell volumes were measured to 9.4 GPa and 767 K by angle dispersive X-ray diffraction using imaging plates. Phase changes were not observed within this pressure-temperature range, and lawsonite compressed almost isotropically at constant temperature. The P-V-T data have been analyzed using a Birch- Murnaghan equation of state and a linear equation of state expressed as β=–1/V0 (∂V/∂P) T . At room temperature, the derived equation of state parameters are: K 0=124.1 (18) GPa K'0 set to 4) and β–1=142.0(24) GPa, respectively. Our results are intermediate between previously reported measurements. The high-temperature data show that the incompressibility of lawsonite decreases with increasing temperature to ∼500 K and then increases above. Hence, the second order temperature derivative of the bulk modulus is taken into account in the equation of state; a fit of the volume data yields K 0=123.9(18) GPa, (∂K/∂T)P=–0.111(3) GPa K–1, (∂2 K/∂T 2)P=0.28(6) 10–3 GPa K–2, α0=3.1(2) 10–5 K–1, assuming K'0=4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050201
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  • 5
    Electronic Resource
    Electronic Resource
    High-temperature thermal expansion of lime, periclase, corundum and spinel (1999)
    Springer
    Physics and chemistry of minerals 27 (1999), S. 103-111 
    Details
    ISSN: 1432-2021
    Keywords: Key words X-ray diffraction ; High-temperature ; Oxides ; Thermal expansion ; Anharmonicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The high-temperature cell parameters of lime (CaO), periclase (MgO), corundum (Al2O3), and spinel (MgAl2O4) have been determined from 300 up to 3000 K through X-ray diffraction experiments with synchrotron radiation. The good agreement found with dilatometric results suggests that vacancy-type defects do not make a large contribution to thermal expansion for these oxides, even near the melting point, justifying the use of X-ray diffraction for determining volume properties up to very high temperatures. Thermal expansion coefficients were determined from the measured cell volumes with equations of the form α=α0 + α1 T + α2/T 2. Along with available isobaric heat capacity and compressibility data, these derived coefficients clearly show that anharmonic effects contribute little to the isochoric heat capacities (C v ) of CaO, MgO, and Al2O3, which do not depart appreciably from the 3nR Dulong and Petit limit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050246
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