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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 366-372 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The 0.255 A(ring)/kbar linear pressure shift of the intense, narrow, and well-isolated 5D0-7F0 (named 0-0) emission line of SrB4O7:Sm2+ (at 6854.1 A(ring) in ambient conditions) is proposed as a new optical pressure gauge for the diamond anvil cell. The pressure determinations can be made with the same experimental devices as those currently used for the ruby sensor. The good accuracy results from the singlet character and a small linewidth which is no more than 2.5 A(ring) up to 200 kbar in a 4:1 methanol:ethanol mixture, provided the linewidth is "relaxed'' through thermal cycles. Such a process can probably be of general interest for this purpose. In nonisostatic media, a similar pressure coefficient and a broadening of ∼0.1 A(ring)/kbar are obtained. This broadening does not greatly disturb the pressure measurements, at least up to 200 kbar. High-pressure determinations up to 400 °C are also shown to be more accurate than with the ruby, owing to the very limited temperature effect on the wavelength (−0.001 A(ring)/°C) and linewidth (∼0.005 A(ring)/°C) of the 0-0 line. The other characteristics of the emission spectrum of SrB4O7:Sm2+ are promising for (a) simultaneous measurements of pressure and temperature (at least up to 400 °C) using this same material and (b) further research on other rare-earth-doped compounds. The possibility of pressure coefficients larger than that of the R1 ruby line is shown by the 0.45 A(ring)/kbar value measured for another emission line of SrB4O7:Sm2+.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The volumes of the pure synthetic pyrope, spessartine and uvarovite garnets have been determined by powder x-ray diffraction as a function of pressure up to 25 GPa in a diamond anvil cell at room temperature. Experiments in different pressure transmitting media have been systematically carried out to determine the effects of anisotropic stress components, which were found to be substantial and have been taken into account. Assuming that the bulk moduli determined from ultrasonic experiments have the lowest uncertainties, the following values for the pressure derivatives of the bulk modulus of uvarovite, spessartine and pyrope were respectively obtained: 4.7±0.7, 7−7.3±1 and 3.4±1. The value for pyrope can be attributed to the small size of the Mg2+ cation in its dodecahedral site.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2021
    Keywords: Key words Germanium dioxide ; High pressure phase transition ; Rietveld refinement
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  Germanium dioxide was found to undergo a transition from the tetragonal rutile-type to the orthorhombic CaCl2-type phase above 25 GPa. The detailed structural evolution of both phases at high pressure in a diamond anvil cell has been investigated by Rietveld refinement using angle-dispersive, X-ray powder-diffraction data. The square of the spontaneous strain (a−b)/(a+b) in the orthorhombic phase was found to be a linear function of pressure and no discontinuities in the cell constants and volume were observed, indicating that the transition is second-order and proper ferroelastic. Compression of the GeO6 octahedra was found to be anisotropic, with the apical Ge-O distances decreasing to a greater extent than the equatorial distances and becoming shorter than the latter above 7 GPa. Above this pressure, the GeO6 octahedron exhibits the common type of tetragonal distortion predicted by a simple ionic model and observed for most rutile-type structures such as those of the heavier group-14 dioxides and the metal difluorides. Above the phase transition, the columns of edge-sharing octahedra tilt about their two fold axes parallel to c and the rotation angle reaches 10.2(5)° by 36(1) GPa so as to yield a hexagonal close-packed oxygen sublattice. The compressibility increases at the phase change as is expected for a second-order transition at which an additional compression mechanism becomes available.
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature genetics 7 (1994), S. 122-123 
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Sir — The fragile X locus locus is flanked by two CA repeat-loci, FRAXAC1 and FRAXA C2, 10 kilobases from the expanded (CGG)n repeat, on the centromeric and telomeric sides, respectively2. On the basis of polymorphisms exhibited by these CA repeats, we and others6,8,9 have shown that some ...
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  • 5
    ISSN: 0921-4534
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The structure of moganite-type phosphorus oxynitride quenched from high-pressure high-temperature conditions has been refined using neutron powder diffraction data. This moganite-type structure, space group I2/a, Z = 12, is slightly less distorted with respect to the Imab aristotype than is moganite (a monoclinic form of silica). A close topological relationship has been identified between the moganite-type and orthorhombic BeH2 structures indicating that SiO2, PON and BeH2 all adopt structures belonging to the twinned-quartz-based group. This group represents another possible structure type for systems composed of corner-sharing AX4 tetrahedra. Structures of this group are obvious candidates for intermediate phases between the cristobalite and quartz types.
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  • 7
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Inorganica Chimica Acta 139 (1987), S. 253-255 
    ISSN: 0020-1693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 2351-2354 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The previously determined optical properties of SrB4O7 ;Sm2+ make this compound a possible better pressure calibrant than ruby, particularly when used at elevated temperatures. Moreover, it can be used with the same experimental devices. In fact, SrB4O7 ;Sm2+ displays an intense emission line which is a nondegenerated singlet, 5D0−7F0, at 685.41 nm in the same spectral range as ruby, 694.22 nm. In the present study, its shift with pressure has been calibrated with the shift of the ruby R1 line up to 60 GPa and has also been recorded to over 100 GPa. No phase transition of SrB4O7 ;Sm2+ was found at least up to 108 GPa. The pressure profiles in the diamond anvil cell have been established at 60 and 105 GPa. In addition, the bulk modulus of SrB4O7 ;Sm2+, B0=170 GPa, has been determined from x-ray diffraction experiments up to 27 GPa. An analytical expression for the shift of the wavelength with pressure is derived and applications to ruby and strontium borate are given.
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