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  • 1
    Digitale Medien
    Digitale Medien
    Nanostructure and atomic ordering in vanadium carbide (1999)
    Springer
    JETP letters 69 (1999), S. 472-478 
    Details
    ISSN: 1090-6487
    Schlagwort(e): 61.46.+w
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Nanostructured nonstoichiometric vanadium carbide VC0.87 was obtained in powdered form using the ordering effect. The composition, structure, and properties of the carbide were studied by chemical and thermogravimetric analysis, gas chromatography, x-ray diffraction, optical and electronic microscopy, electron-positron annihilation, magnetic susceptibility, and microhardness methods. Nanostructured vanadium carbide VC0.87 possesses the crystal structure of the cubic ordered phase V8C7 with space group P4332. Vanadium carbide nanocrystallites are shaped in the form of 400–600 nm in diameter and 15–20 nm thick curved petals. The surface layer of the nanocrystallites contains defects of the vacancy agglomerate type. The microhardness of vanadium carbide, obtained by vacuum sintering of VC0.87 nanopowder was 60–80 GPa, which is 3–4 times greater than the microhardness of coarse-grained vanadium carbide with the same composition and close to the hardness of diamond.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.568054
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  • 2
    Digitale Medien
    Digitale Medien
    Magnetic properties of a monocrystalline quasicrystal in the Al-Pd-Mn system (2000)
    Springer
    JETP letters 72 (2000), S. 144-147 
    Details
    ISSN: 1090-6487
    Schlagwort(e): 75.50.Kj ; 75.0.Ej ; 61.44.Br
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Magnetic susceptibility of a monocrystalline icosahedral Al70.2Pd21.3Mn8.5 quasicrystal was measured over the temperature range from 4 to 1100 K. The susceptibility was found to include the temperature-independent diamagnetic contribution, the temperature-dependent Curie’s contribution, and the contribution from the Pauli paramagnetism of an electron system with energy gap. An analysis of the low-temperature susceptibility revealed the presence of about 0.008% of ions with magnetic moment 4µB in the quasicrystal at 4 K. It is assumed that the ions with uncompensated magnetic moments appear near the structural vacancies in the quasicrystal lattice. The energy gap between the valence and conduction bands is estimated at Δ=0.64 eV, and the effective mass of charge carriers is equal to approximately 70 electron masses.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.1316819
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  • 3
    Digitale Medien
    Digitale Medien
    Irradiation-induced atomic defects in SiC studied by positron annihilation (1995)
    Springer
    Applied physics 61 (1995), S. 51-53 
    Details
    ISSN: 1432-0630
    Schlagwort(e): PACS: 61.70; 61.80; 78.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract.  The present paper reports on positron lifetime measurements on atomic defects in SiC after low-temperature (80 K) electron irradiation of low (0.47 MeV) and high (2.5 MeV) electron energies and doses from 1.8×1017 to 1.9×1019 e/cm2 as well as after subsequent isochronal annealing up to 1900 K. For these studies the single crystals of nitrogen doped (2-3×1018 cm-3) SiC grown by a modified Lely technique with hexagonal structure (6H polytype) were used. According to the positron lifetime measurements, very different types of vacancy-like positron traps are introduced after irradiation with electrons of either low or high energy. The formation of defect agglomerates and their decay at high temperatures is studied during isochronal annealing and related to earlier studies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01538210
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  • 4
    Digitale Medien
    Digitale Medien
    Irradiation-induced atomic defects in SiC studied by positron annihilation (1995)
    Springer
    Applied physics 61 (1995), S. 51-53 
    Details
    ISSN: 1432-0630
    Schlagwort(e): 61.70 ; 61.80 ; 78.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The present paper reports on positron lifetime measurements on atomic defects in SiC after low-temperature (80 K) electron irradiation of low (0.47 MeV) and high (2.5 MeV) electron energies and doses from 1.8×1017 to 1.9×1019 e/cm2 as well as after subsequent isochronal annealing up to 1900 K. For these studies the single crystals of nitrogen doped (2–3×1018 cm−3) SiC grown by a modified Lely technique with hexagonal structure (6H polytype) were used. According to the positron lifetime measurements, very different types of vacancy-like positron traps are introducted after irradiation with electrons of either low or high energy. The formation of defect agglomerates and their decay at high temperatures is studied during isochronal annealing and related to earlier studies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01538210
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  • 5
    Digitale Medien
    Digitale Medien
    Two-sublattice ordering in titanium monoxide (2000)
    Springer
    JETP letters 71 (2000), S. 460-464 
    Details
    ISSN: 1090-6487
    Schlagwort(e): 61.50.Ks ; 61.66.Fn; 61.50.Nw
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The disordered and ordered structures of nonstoichiometric titanium monoxide TixOz≡TiOy(y=z/x) containing structural vacancies simultaneously in the nonmetallic and metallic sublattices were studied. In the stoichiometry range from TiO0.9 to TiO1.1, an ordered monoclinic phase [space group C2/m (A12m/1)] of the Ti5O5 type is formed in the TiOy monoxide at temperatures below 1300 K. The disorder-order TiOy−Ti5O5 phase-transition channel involves Lifshitz {k10} and non-Lifshitz {k4} and {k11} star rays. The ordering proceeds as a first-order phase transition with a decrease in the volume of the basal cubic lattice. The titanium and oxygen distribution functions in the metallic and nonmetallic sublattices of titanium monoxide are calculated. The domain of allowed values is determined for the long-range order parameter.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.1307993
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  • 6
    Digitale Medien
    Digitale Medien
    Preparation of disordered and ordered highly nonstoichiometric carbides and evaluation of their homogeneity (2000)
    Springer
    Physics of the solid state 42 (2000), S. 1280-1286 
    Details
    ISSN: 1063-7834
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The features of solid-phase synthesis of highly nonstoichiometric carbides with controlled concentration of structural vacancies in the carbon sublattice have been considered. Four main stages are distinguished in the synthesis of nonstoichiometric carbides by the solid-phase sintering technique. It is shown that the inhomogeneity of highly nonstoichiometric compounds leads to the broadening of diffraction reflections. The analytical relation between the broadening and the inhomogeneity is obtained for the first time, and the method based on diffraction measurements is proposed for the quantitative evaluation of the degree of homogeneity of nonstoichiometric compounds. As an illustration of the advanced approach, the degree of homogeneity of nonstoichiometric niobium carbide is evaluated from the experimental data on the width of x-ray diffraction peaks. The heat treatment conditions providing the preparation of nonstoichiometric Group IV and V transition metal carbides in the disordered and ordered states are determined.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1134/1.1131377
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