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  • 1990-1994  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Electron paramagnetic resonance of defects in β-iron disilicide ceramics (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1693-1698 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The point defects in β-iron disilicide ceramics, which may influence the thermoelectric properties of the ceramics, have been investigated by electron paramagnetic resonance (EPR). The 77-K EPR spectra are dependent upon the Si/Fe ratio of the ceramics specimens. Several S=1/2 centers with g factors of about 2.0 are observed in both silicon-deficient p-type and iron-deficient n-type specimens prepared by sintering and subsequent annealing of FeSix(1.9〈x〈2.8) grains. These centers disappear in a specimen prepared by directly annealing a lump of FeSi2 alloy without sintering. By considering the difference of the sample-preparation procedures, we conclude that the S=1/2 centers exist in the oxidized intergrain region of the ceramics. An S=1/2 signal with an anisotropic g factor (g1=2.061, g2=2.047, g3=2.024) arises only in iron-deficient n-type specimens. This signal is attributable to unionized donor electrons. A multiplet signal with zero-field splitting arises in nearly stoichiometric p-type specimens. The multiplet signal is explained in terms of an S=3 center. Several possible models based on exchange interaction between two spins were examined to elucidate the origin of the S=3 center. The most plausible model is the pair of a high spin Fe3+ (S=5/2) and an S=1/2 center (a silicon vacancy or an acceptor hole).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356356
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Point defects and thermoelectric properties of iron disilicide ceramics sintered with SiH4-plasma-processed micrograins (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2097-2103 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The point defects in β-iron disilicide (β-FeSi2) have been investigated by electron paramagnetic resonance (EPR) along with the thermoelectric properties. The samples used are FeSix (1.9≤x≤2.8) ceramics sintered with FeSix micrograins processed in SiH4-plasma and nonprocessed. EPR detects (1) several S=1/2 signals and (2) a multiplet signal. An S=1/2 signal with orthorhombic g factors (g1=2.061, g2=2.047, g3=2.024) is detected in all n-type specimens, and ascribed to unpaired electrons of donors associated with iron vacancies. The other S=1/2 signals are detected in both n-type and p-type specimens. The centers responsible for these signals are considered to exist in an oxidized intergrain region of the ceramics. The EPR intensity of the multiplet signal due to the closed-pair of a high spin Fe3+ ion (S=5/2) and an S=1/2 center is reduced by SiH4-plasma treatments. SiH4-plasma processing of FeSix micrograins prior to sintering changes the Seebeck coefficient sign and magnitude, depending upon the condition of plasma processing. This Seebeck change is explained in terms of the introduction of silicon- and/or iron-vacancies. SiH4-plasma processing increases the electrical conductivity of nearly stoichiometric specimens and reduces the EPR intensity of the multiplet signal. A possible model for the increased conductivity is discussed using an energy band model for the ceramic grains and grain boundaries. We consider that the change of the thermoelectric properties by SiH4-plasma processing is mainly due to the modification of defects in and near the ceramic intergrain region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357620
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Possible selective effects of Interferon α-2b on a malignant clone in a case of polycythemia vera (1993)
    Springer
    Annals of hematology 66 (1993), S. 161-162 
    Details
    ISSN: 1432-0584
    Keywords: Polycythemia vera ; Interferon ; Translocation, IgA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A patient with polycythemia vera associated with chromosomal translocation (6; 8) (q27; p11) and IgA monoclonal gammopathy was treated with interferon α-2b. Interferon α-2b induced good hematological control and reduced only IgA levels, but not IgG and IgM levels. In addition, cytogenetic improvement was obtained, the abnormal cells with chromosomal translocation declining from 100% to 50%. Interferon a may have selective effects on a malignant clone in polycythemia vera.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01697629
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    Paper (German National Licenses)
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