Search Results - (Author, Cooperation:S. Kamba)

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  1. 1
    Staff View
    Publication Date:
    2011-07-08
    Publisher:
    Nature Publishing Group (NPG)
    Print ISSN:
    0028-0836
    Electronic ISSN:
    1476-4687
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Published by:
    http://www.nature.com/

    Latest Papers from Table of Contents or Articles in Press
  2. 2
    Staff View
    Publication Date:
    2013-10-18
    Publisher:
    Nature Publishing Group (NPG)
    Print ISSN:
    0028-0836
    Electronic ISSN:
    1476-4687
    Topics:
    Biology
    Chemistry and Pharmacology
    Medicine
    Natural Sciences in General
    Physics
    Published by:
    http://www.nature.com/

    Latest Papers from Table of Contents or Articles in Press
  3. 3
    Kamba, S. ; Petzelt, J. ; Buixaderas, E. ; Haubrich, D. ; Vanek, P.

    [S.l.] : American Institute of Physics (AIP)
    Published 2001
    Staff View
    ISSN:
    1089-7550
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    High-frequency dielectric properties of A5B4O15 (A=Ba, Sr, Mg, Zn, Ca; B=Nb, Ta) dielectric ceramics are studied by means of the microwave cavity technique, a combination of far-infrared reflection and transmission spectroscopy and time-resolved terahertz transmission spectroscopy. Microwave permittivity ε′ and Q×f factor vary, depending on the chemical composition, between 11 and 51, and 2.4 and 88 THz, respectively. The temperature coefficient τf varies between −73 and 232 ppm/°C, and in two samples |τf| is less than 15 ppm/°C. It is shown that the microwave permittivity ε′ of the ceramics studied is determined by the polar phonon contributions and that linear extrapolation of the submillimeter dielectric loss ε″ down to the microwave region is in agreement with the microwave data of single phase samples. The relationship among phonon spectra, the crystal structure, and the unit cell volume is discussed. © 2001 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.1351873

    Articles: DFG German National Licenses
  4. 4
    Kamba, S. ; Pokorný, J. ; Porokhonskyy, V. ; Petzelt, J.

    Woodbury, NY : American Institute of Physics (AIP)
    Published 2002
    Staff View
    ISSN:
    1077-3118
    Source:
    AIP Digital Archive
    Topics:
    Physics
    Notes:
    Polarized microscope observation of ferroelastic domains in a SrBi2Ta2O9 (SBT) single crystal reveals the presence of domains up to Tc1(similar, equals)770 K, which supports the ferroelasticity and Amam symmetry of the intermediate phase between ferroelectric and paraelectric phases. Far-infrared spectra of SBT ceramics, single crystal and thin films show a well underdamped optical soft mode at 28 cm−1, which partially softens to 21 cm−1 near the ferroelectric transition temperature (Tc2≅600 K). This softening does not explain the entire anomaly of low-frequency permittivity observed near Tc2. On the basis of high-frequency measurements, which do not show a significant dispersion, central-mode-type dispersion in the 10–100 GHz range is proposed as an explanation. So, the phase transition at Tc2 apparently shows a crossover behavior between the displacive and the order–disorder type. © 2002 American Institute of Physics.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1063/1.1498005

    Articles: DFG German National Licenses
  5. 5
    Staff View
    ISSN:
    0022-2860
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Chemistry and Pharmacology
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://linkinghub.elsevier.com/retrieve/pii/0022-2860(90)80037-K

    Articles: DFG German National Licenses
  6. 6
    Staff View
    ISSN:
    0038-1098
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://linkinghub.elsevier.com/retrieve/pii/0038-1098(90)90416-9

    Articles: DFG German National Licenses
  7. 7
    Staff View
    ISSN:
    0038-1098
    Source:
    Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics:
    Physics
    Type of Medium:
    Electronic Resource
    URL:
    http://linkinghub.elsevier.com/retrieve/pii/0038-1098(89)90947-2

    Articles: DFG German National Licenses
  8. 8
    Kamba, S. ; Petzelt, J. ; Zelezný, V.
    Springer
    Published 1986
    Staff View
    ISSN:
    1572-9486
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Physics
    Notes:
    Abstract The polarized reflectivity of BaMnF4 single crystals was measured in the 20–600 cm−1 range for temperatures from 10 to 300 K. The results were evaluated using Kramers-Kronig analysis to obtain the dielectric function. The number of active modes in the high temperature polar phase (T〉T i ≃250K) is in agreement with group-theoretical expectation. In the incommensurate phaseT〈T i the number of active modes increases more than two times. All the results are in reasonable agreement with previous Raman and far infrared data.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF01598334

    Articles: DFG German National Licenses
  9. 9
    Ferreira, V. M. ; Baptista, J. L. ; Kamba, S. ; Petzelt, J.
    Springer
    Published 1993
    Staff View
    ISSN:
    1573-4803
    Source:
    Springer Online Journal Archives 1860-2000
    Topics:
    Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes:
    Abstract Magnesium titanate (MgTiO3) powder was prepared by a chemical route (Pechini method) and different dopants were added to prepare several compositions. These pure and doped compositions were sintered in air and dense ceramics were obtained. The pure MgTiO3 samples were also subjected to different heat treatments during sintering. Complex permittivity spectra of ceramic samples were determined by various techniques in the 109–1014 Hz range. These techniques included infrared spectroscopy in transmission and reflectivity modes and microwave dielectric measurements. Extrapolation to microwave frequencies from infrared data, according to the proportionality ɛ″(v) ∝ v, agrees quite well with the microwave data measured at 8 GHz and it is a useful procedure to estimate intrinsic microwave losses. Fast cooling from high temperatures of MgTiO3 samples increased dielectric loss, probably due to a structural disorder. Dopants have two types of effect depending on whether they form a distinct second phase or a solid solution with MgTiO3. In this last case intrinsic losses are strongly affected.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1007/BF00365198

    Articles: DFG German National Licenses
  10. 10
    Kulek, J. ; Hilczer, B. ; Kamba, S. ; Petzelt, J.

    Weinheim : Wiley-Blackwell
    Published 1995
    Staff View
    ISSN:
    0323-7648
    Keywords:
    Chemistry ; Polymer and Materials Science
    Source:
    Wiley InterScience Backfile Collection 1832-2000
    Topics:
    Chemistry and Pharmacology
    Physics
    Notes:
    We studied the influence of hot-pressing temperature as well as poling and ageing conditions on the amount of polar phase of hot-pressed PVDF and P(VDF/TFE)-(0.98/0.02) foil. FIR transmission spectra of hot-pressed homopolymer and copolymer films were measured in the 30-450 cm - 1 range as a function of hot-pressing temperature Thp and poling temperature Tp. The FIR studies show that homopolymer and copolymer consist of both polar and nonpolar modifications of PVDF. The content of the polar phase tends to decrease with Thp and increase after poling. The FIR spectra of our samples exhibit a strong absorption peak near 100 cm - 1 absent in the biaxially oriented Solef samples, which is believed to be due to the amorphous phase in our samples. Four thermally stimulated current (TSC) maxima are attributed to the relaxation in the amorphous region (∼40°C), to the dipolar relaxation in the nonpolar (∼60°C) and polar (∼80°C) phase, and the space charge relaxation (dependent on the poling temperature). The pyroelectric coefficient of the homopolymer and copolymer thermoelectret foil prepared by hot-pressing is of the same order as that of the PVDF thermoelectret foil produced by Solvay and can be influenced by the hot-pressing conditions. The dielectric response of the hot-pressed PVDF-type foils can be described by the Kohlrausch--Williams-Watts function and is characteristic of a heterogeneous system.
    Additional Material:
    10 Ill.
    Type of Medium:
    Electronic Resource
    URL:
    http://dx.doi.org/10.1002/actp.1995.010460209

    Articles: DFG German National Licenses