Browsing by Author "Zamboni, Roberto"

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    Assignment of fundamental vibrations and estimation of electron-molecular vibration coupling constants for bis(ethylenedioxy)tetrathiafulvalene (BEDO)
    (1993) Pokhodnia, Konstantin I.; Kozlov, Mikhail E.; Onischenko, V. G.; Schweitzer, Dieter; Moldenhauer, Jörg; Zamboni, Roberto
    The 1.r. absorption and Raman spectra of BEDO are investigated. All fundamental vibrations are assigned using correlations between the obtained data and those for a well-known compound BEDT-TTF (ET). Comparative normal coordinate analysts has been done. The results are used for calculation of electron-intramolecular vibration coupling constants of BEDO based superconducting charge-transfer complexes. Comparison of these values with the constants obtained earlier for ET shows that BEDO is a perspective donor for searching new superconductors on its basis.
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    Bulk superconductivity at ambient pressure in polycrystalline pressed samples of organic metals
    (1990) Schweitzer, Dieter; Kahlich, Siegfried; Gärtner, Stephan; Gogu, Emil; Grimm, Hans; Zamboni, Roberto; Keller, Heimo J.
    Bulk superconductivity in polycrystalline pressed samples of αt-(BEDT-TTF)2I3 and βp-(BEDT-TTF)2I3 is reported. This finding shows that organic superconductors can be used in principle for the preparation of electronic devices and superconducting cables.
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    Bulk superconductivity in polycrystalline pressed samples of αt-(BEDT-TTF)2I3 and βp-(BEDT-TTF)2I3
    (1990) Schweitzer, Dieter; Kahlich, Siegfried; Gärtner, Stephan; Gogu, Emil; Grimm, Hans; Zamboni, Roberto; Keller, Heimo J.
    Bulk superconductivity at ambient pressure in pressed samples of polycrystalline αt-(BEDT-TTF)2I3 and βp-(BEDT-TTF)2I3 is reported. This finding is remarkable because it demonstrates that organic superconductors can be used in principal for applications such as the preparation of electronic devices and superconducting cables. In addition the observation of bulk superconductivity in large pressed samples of crystallites of a typical diameter of 1μm of organic metals indicates that superconductivity in organic polymers should be observable as well.
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    FT-IR absorption spectra of polycrystalline pressed samples of the organic metals and superconductors α-, β-(BEDT-TTF)2I3 and (BEDT-TTF)2Cu(NCS)2
    (1989) Zamboni, Roberto; Schweitzer, Dieter; Keller, Heimo J.; Taliani, Carlo
    IR absorption spectra of polycrystalline pressed samples of the organic metals α-(BEDT- TTF)2I3, β-(BEDT-TTF)2I3 and (BEDT-TTF)Cu(NCS) are presented and discussed. Normal prononated as well as deuterated materials were studied. The spectra range from 400 cm-1 to 5000 cm-1 and are similar to the IR reflectance spectra reported earlier. The data are of special interest in view of the fact that recently bulk superconductivity was observed in such polycrystalline samples of organic metals, and therefore the application of organic superconductors for the preparation of electronic devices seems possible.
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    (FT-NIR) Raman scattering in pressed pellets of BEDT-TTF based organic metals
    (1991) Zamboni, Roberto; Schweitzer, Dieter; Keller, Heimo J.
    The low lying (1.25 eV) electronic state of a family of BEDT-TTF based organic metals has been investigated with FT-NIR resonant Raman scattering. We assign the 1.25 eV electronic state to the BEDT-TTF cation radical. The enhanced Raman modes coupled with this electronic transition are discussed and assigned.
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    Raman investigations on single crystals and polycristalline pressed samples of organic superconducters
    (1991) Zamboni, Roberto; Schweitzer, Dieter; Keller, Heimo J.
    The investigation of molecular vibrations is a powerful tool which can increase our knowledge on structures and on electron molecular vibrations, which are due to charge oscillation between dimerized moIecuIes,coupled with totally symmetric intramolecular modes. Raman scattering studies account for totally symmetric vibrations. In addition, Raman spectroscopy can take advantage of resonant effects. In fact, when resonant conditions are fulfilled, selected molecular vibrations are obtained as well as information on the electronic manifold involved in the resonance process. In this paper, we report on Raman investigations of polycrystalline pressed materials of superconducting tempered -α(BEDT-TTF)2I3, called in the following, αt-{BEDT-TTF)2I3 and on untempered α(BEDT-TTF)2I3. Furthermore we report on the polarized resonant Raman scattering in the superconducting regime of (BEDT-TTF)2Cu(NCS)2 single crystals.
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    Resonant Raman scattering on single crystals of (BEDT-TTF)2Cu(NCS)2
    (1990) Zamboni, Roberto; Schweitzer, Dieter; Keller, Heimo J.
    Resonant Raman spectra of the organic superconductor (BEDT-TTF)2Cu(NCS)2 have been measured at 1.3 K as well as at 120 K. The Raman data do not show a superconducting gap opening in the investigated two dimensional superconducting system. The vibrational modes found in the Raman spectra are discussed and assigned. Possible mechanisms for resonance conditions in such two-dimensional organic superconducting systems are proposed.
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    Transport properties of single crystals and polycristalline pressed samples of (BEDT-TTF)2X salts and related coordination polymers
    (1991) Schweitzer, Dieter; Kahlich, Siegfried; Gärtner, Stephan; Gogu, Emil; Grimm, Hans; Heinen, Ilsabe; Klutz, Thomas; Zamboni, Roberto; Keller, Heimo J.; Renner, Gerd
    Ten years ago in 1979, superconductivity was observed for the first time in an organic metal. today, about 30 different organic metals are known, which become superconducting under pressure or ambient pressure. The organic superconductors with the highest transition temperatures are all radical salts of the donor bis(ethylenedithioio)-tettathiafulvalene (BEDT-TTF), namely at ambient pressure (BEDT-TTF)2CU(NCS)2 (Tc = 10.4 K) and αt,-(BEDT-TTF)2I3 (Tc = 8 K) and under isotropic pressure β H- (BEDT-TTF)2I3(0.5 kbar, Tc = 7.5 K) The latter β H-phase can even become superconducting at 8 K and ambient pressure, after a special pressure-temperature cycling procedure i.e. pressurization up to 1 kbar at room temperature, and release of the helium gas pressure at temperarures below 125 K. Nevertheless, this superconducting state at 8 K in β H-(BEDT -TTF)2I3 is only metastable , since warming up the crystal above 125 K and cooling down again under ambient pressure, results only in superconductivity at 1.3 K, the so-called β L - or β-phase.