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  • 1
    Digitale Medien
    Digitale Medien
    Effects of deviatoric stress and radial strain on the shock-induced diffusionless transformation in boron nitride (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 527-529 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The phase transformation of graphitelike BN (h-BN) to wurtzite-type high-pressure BN (w-BN) was investigated through shock-recovery techniques under quasihydrodynamic and nonhydrodynamic shock compressions and under various strain conditions. The experimental results support a diffusionless mechanism, by which the hydrodynamic c-axis compression of h-BN is preferred. This mechanism is topologically considered based on the relationship of crystal structures between h-BN and w-BN. The presence of deviatoric stress and strain depresses the yield of w-BN and the development of w-BN (100) relative to (002). © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.364132
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  • 2
    Digitale Medien
    Digitale Medien
    High-resolution transmission electron microscopy of cubic Si3N4 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 3070-3072 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A cubic Si3N4 phase/nanostructure has been characterized by means of high-resolution analytical electron microscopy. The specimen prepared from β-Si3N4 powders at a high pressure and temperature by shock wave compression contained nanometer-sized Si3N4 crystallites. The results of nano-beam electron diffraction analysis and high-resolution lattice images as well as computer simulations revealed that the Si3N4 crystallites had a cubic symmetry with spinel structure. The electron energy loss spectrum suggested that the chemical compositions of these nanostructures were close to Si3N4. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1287765
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  • 3
    Digitale Medien
    Digitale Medien
    Phase transformation of germanium nitride (Ge3N4) under shock wave compression (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4403-4406 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The phase transformation behavior of hexagonal germanium nitride, including both α- and β-Ge3N4, has been studied under shock wave compression. The shock compressed quenched samples indicate phase transformation from hexagonal into a cubic spinel structure (γ-Ge3N4). This transformation is completed with increasing shock pressure up to 40–46 GPa (temperature of 1300–1500 K). The lattice constant of γ-Ge3N4 is measured to be 0.820 63±0.000 19 nm, and the crystal density 6.581 g/cm3, by the powder x-ray diffraction. The stability of γ-Ge3N4 also has been investigated under shock wave compression. It is found that the spinel structure is very stable, and up to at least 63 GPa (temperature of ∼1700 K) there is no indication of the formation of a postspinel phase. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1407851
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  • 4
    Digitale Medien
    Digitale Medien
    Time-resolved measurement on ablative acceleration of foil plates driven by pulsed laser beam (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 2032-2035 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Coupled with the push-pull type velocity interferometer system for any reflector, an electronic streak camera recording system has been established, which provides subnanosecond time resolution in the detection of interferential fringes. Complete acceleration histories of Al, Au, and Pt foil plates, driven by pulsed laser beam at 30–400 GW/cm2, have been measured by using this system. For the 10-μm-thick Al foil irradiated at 280 GW/cm2, an ablative acceleration up to terminal velocity about 9 km/s within 25 ns has been determined with a velocity uncertainty of ∼1%. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1357227
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  • 5
    Digitale Medien
    Digitale Medien
    Radiation temperatures of soda-lime glass in its shock-compressed liquid state (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 1711-1716 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A radiation pyrometer in conjunction with a two-stage light gas gun has been used to measure shock temperatures of soda-lime glass in the pressure range 54–109 GPa. This pyrometer consists of two parts, i.e., an optical multichannel analyzer which measures the radiation spectrum over the visible range (∼450 nm window) and a four-channel photomultiplier tube system which records the time-varying behavior of shock temperatures. The measured radiation spectra are compared with the Planck function to estimate the shock temperatures and emissivities. Obtained spectra are well fit by the Planck function with moderate emissivities, indicating that relatively homogeneous thermal radiation is the main component of radiation. Obtained shock temperatures range from 2800 (100) to 5700 (300) K and they seem to represent shock temperatures of liquefied soda-lime glass (melt). The Hugoniot is well described by a linear relation, us=0.14(21)+1.92(5)up km/s. It is deduced that the radiation from liquids under shock compression, in contrast to the radiation from solids under shock compression, is more thermal and fits the Planck function well, even at lower temperatures. This is because the radiation spectrum of solids under compression often shows nonthermal radiation due to heterogeneous deformation, while the radiation spectrum of liquids under compression could not have such a nonthermal component. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.366889
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  • 6
    Digitale Medien
    Digitale Medien
    High-temperature metastability of cubic spinel Si3N4 (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 2719-2721 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The metastability of cubic spinel Si3N4 has been investigated at high temperature, up to about 1800 K, and in Ar atmosphere by quench experiments and differential thermal analyses coupled with thermogravimetry. The results indicate that the enthalpy change from spinel-type Si3N4 to β-Si3N4 is −29.2±3.5 kJ/mol and that the transformation starts at 1670 K. The high-temperature metastability of spinel Si3N4 may provide various directions for industrial applications. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1412826
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  • 7
    Digitale Medien
    Digitale Medien
    Shock-induced transformation of β-Si3N4 to a high-pressure cubic-spinel phase (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3706-3708 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: β-Si3N4 powders were shock compressed and quenched from 12 to 115 GPa. β-Si3N4 transforms to the spinel-type Si3N4 (c-Si3N4) by a fast reconstructive process at pressures above about 20 GPa. The yield of c-Si3N4 recovered from 50 GPa and about 2400 K reaches about 80% and the grain sizes are about 10–50 nm. It is proposed that the fast transformation to c-Si3N4 occurs by rearrangement of nitrogen stacking layers, which initiates partial breakup of the SiN4 tetrahedra and formation of SiN6 octahedra at high density. Because of the advantages of massive production and the nanometer characteristics of shock-synthesized c-Si3N4, it is possible to investigate the mechanical properties experimentally and to develop new industrial applications. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.126756
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  • 8
    Digitale Medien
    Digitale Medien
    29Si magic-angle-spinning nuclear-magnetic-resonance study of spinel-type Si3N4 (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 3050-3051 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: 29Si magic-angle-spinning nuclear-magnetic resonance has been measured on spinel-type cubic silicon nitride (c-Si3N4). c-Si3N4 shows two 29Si resonances at −50.0±0.2 and −225.0±0.2 ppm, corresponding to the tetrahedron SN4 and the octahedron SiN6, respectively. Integration of the spectrum gives SN4/SiN6 about one half that of the spinel structure. Ab initio self-consistent field Hartree–Fock molecular orbital calculations also indicate that the chemical shift for octahedral Si is more negative in nitride than in oxides. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1372199
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  • 9
    Digitale Medien
    Digitale Medien
    Sixfold-coordinated carbon as a postdiamond phase (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 350-352 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Carbon behavior at extremely high pressures, which at present cannot be investigated by direct experiments, was evaluated based on high-pressure experimental results on various SiC and NaCl-type carbides. Sixfold-coordinated carbon C(VI) was determined to be the most probable candidate for the postdiamond phase. Taking into account structural variations in the corresponding metals, the volume of C(VI) is estimated to be 3.08 cm3/mol at ambient conditions and 2.8 cm3/mol at pressures of 100–250 GPa. The postdiamond phase of C(VI) may display a greater zero-pressure bulk modulus than diamond. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.123068
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  • 10
    Digitale Medien
    Digitale Medien
    Direct transformation of cubic diamond to hexagonal diamond (2002)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 81 (2002), S. 610-612 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: For a long time, hexagonal diamond has been formed only by static and shock wave compression of well-crystallized graphites. Here, we demonstrate that cubic diamond loses its structure stability and transforms to hexagonal diamond in massive. This transformation has been completed in nanoseconds under a shock wave compression of cubic diamond, in which the shock pressure and temperature are only tens of giga pascal and hundreds of kelvin, thermodynamically being within the stability of cubic diamond. The formation of hexagonal diamond is interpreted as a direct transition (solid to solid) of cubic diamond by a kinetic mechanism due to the shear stress and enhanced temperature induced by the rapid shock wave compression. © 2002 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1495078
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