Universität Stuttgart

Permanent URI for this communityhttps://elib.uni-stuttgart.de/handle/11682/1

Browse

Subject: search.filters.subject.530Institute: search.filters.UBSInstitut.Sonstige EinrichtungStart date: 1986End date: 1987Author: search.filters.author.Keller, Heimo J.

Search Results

Now showing 1 - 10 of 30
  • Thumbnail Image
    ItemOpen Access
    Molecular solids containing BEDT-TTF and structurally related transition metal complexes
    (1986) Keller, Heimo J.; Niebl, Roland; Nöthe, Dietrich; Schweitzer, Dieter; Weber, Angelika
    The special physical properties of BEDT-TTF salts, e.g. their two-dimensional behaviour, are caused by the typical geometry of this donor and the arrangement of the cations in the crystal lattice of its salts. In order to extend the range of physical properties produced by BEDT-TTF like compounds, we synthesized sulfur containing transition metal complexes with a molecular structure very similar to BEDT-TTF. The bis(5.6-dihydro-1.4-dithin-2.3-dithiolate)metallates of the nickel triad can be prepared in different oxidation states as anions and in neutral form. The anionic complexes can be reacted with BEDT-TTF cations.
  • Thumbnail Image
    ItemOpen Access
    Metallic coordination polymers using CS2 as starting material
    (1987) Keller, Heimo J.; Klutz, Thomas; Münstedt, Helmut; Renner, Gerd; Schweitzer, Dieter
    Organic polymers with "metallic" properties have found widespread interest during the last few years. Acetylene and aniline as well as different nitrogen and sulfur heterocycles have been used as starting materials. One main problem hampering the technical application of these solids up to now is their environmental and thermal instability. Therefore, we introduced metal ions to stabilize polymeric backbones with high electrical conductivity. Because of the enormous coordination ability of sulfur to many transition metal ions we decided to use a polymeric carbon-sulfur backbone.
  • Thumbnail Image
    ItemOpen Access
    New charge tranfer salts containing BEDT-TTF and structurally related transition metal complexes
    (1987) Keller, Heimo J.; Niebl, Roland; Nöthe, Dietrich; Schweitzer, Dieter; Weber, Angelika
    The two-dimensional behaviour of BEDT-TTF salts is normally explained with the typical geometry of this donor and its arrangement in the crystal lattice. In order to extend the range of physical properties produced by BEDT-TIF like compounds, we synthesized sulfur containing transition metal complexes with a molecular structure very similar to BEDT-TTF. The bis(5,6-dihydro-1,4-dithiin-2,3-dithiolate)metallates of the nickel triad can be prepared in different oxidation states as anions and in a fully oxidized neutral form.
  • Thumbnail Image
    ItemOpen Access
    ODMR of triplet states of organic electron donors
    (1986) Grimm, Hans; Schweitzer, Dieter; Hausser, Karl H.; Keller, Heimo J.
    Energies of the first excited triplet states and triplet zero field splitting parameters /D/ and /E/ of several organic donors - usually used for the preparation of organic metals and superconductors - are reported.
  • Thumbnail Image
    ItemOpen Access
    Two superconducting phases in the organic conductor: β-(BEDT-TTF)2I3
    (1986) Creuzet, Francois; Bourbonnais, Claude; Creuzet, Gerard; Jerome, Denis; Schweitzer, Dieter; Keller, Heimo J.
    We have investigated the nature and the stability of the high-Tc(∼8 K) and low-Tc (∼1.5 K)superconducting phases (respectively called β-H and β-L) of the organic conductor β-(BEDT-TTF)2I3. First, by resistivity measurements and following a well-defined temperature-pressure cycling process, we show that the β-H phase is stabilized at ambient pressure and low temperature, exhibiting a very sharp and complete superconducting transition at 8.1 K and 1 bar. Secondly, an AC-susceptibility study reveals that this state is stable and exhibits bulk superconductivity at high Tc and ambient P as long as the sample is not warmed above 125 K. Finally, we present NMR results on the 1H spin-lattice relaxation rate behaviour in both the β-H phase and the β-L phase.
  • Thumbnail Image
    ItemOpen Access
    The high-Tc superconducting state of β-(BEDT-TTF)2I3 at atmospheric pressure: bulk superconductivity and metastability
    (1986) Creuzet, Francois; Jerome, Denis; Schweitzer, Dieter; Keller, Heimo J.
    The AC susceptibility study of β-(BEDT-TTF)2I3 reveals that the high-Tc metastable superconducting state which can be stabilized at atmospheric pressure after a particular pressure-temperature cycling procedure, exhibits bulk superconductivity resembling very closely that of the high-Tc state, which is stabilized above 1 kbar. Annealing experiments show that the high-Tc state remains stable at low temperature as long as the annealing temperature does not exceed 125 K.
  • Thumbnail Image
    ItemOpen Access
    Radical cation salts of BEDT-TTF and an unsymmetrical BEDT-TTF derivative
    (1986) Schweitzer, Dieter; Bender, Klaus; Endres, Helmut; Gärtner, Stephan; Heid, Rolf; Heinen, Ilsabe; Keller, Heimo J.; Weber, Angelika; Weger, Meir
    Investigations of several BEDT-TTF and DIMET radical salts are presented. Measurements on β-(BEDT-TTF)2IAuI crystals show that their conducting and superconducting properties might vary strongly depending on the decomposition of (IAuI)− anions during the electrochemical process.
  • Thumbnail Image
    ItemOpen Access
    The effect of disorder on the conduction electron spin resonance linewidth of the α and β phases of (BEDT-TTF)2I3
    (1987) Forró, Laszlo; Schweitzer, Dieter; Keller, Heimo J.
    We present the electron spin resonance linewidth of α and β phases of the organic conductor di-bis (ethylenedithiolo) tetrathiafulvalene driiodide [(BEDT-TTF)2I3] disordered by fast electron irradiation. In the high temperature metallic phase the linewidth decreases in both phases with defect concentration in contrast to the predictions of the Elliott mechanism for spin relaxation in metals.
  • Thumbnail Image
    ItemOpen Access
    Thermal expansion of the organic conductor β-(BEDT-TTF)2I3
    (1986) Hamzic, Bojana; Creuzet, Gerard; Schweitzer, Dieter; Keller, Heimo J.
    We report high resolution thermal expansion measurements between 1.2 and 300 K along the c*-axis in the organic conductor β-(BEDT-TTF)2I3 where the superconducting properties are strongly dependent on the way the system is prepared in the pressure-temperature diagram. We clearly observed a strong anomaly at 172 K related to the structural phase transition and the resistivity anomalies reported by several groups. The temperature analysis in the low temperature regime is coherent with a phonon dominant contribution. Finally, the presence of small hysteresis in a large region around the transitions seem to indicate why both the pressure and the temperature cycling may stabilize small regions of the high-Tc phase of the system, as observed.
  • Thumbnail Image
    ItemOpen Access
    Frequency-dependent conductivity in pure and iodine-doped α-(BEDT-TTF)2I3
    (1987) Przybylski, Michael; Helberg, Hans W.; Schweitzer, Dieter; Keller, Heimo J.
    Measurements of the microwave conductivity at 10 GHz show a plateau below the metal-insulator transition at 135 K in contrast to the further dropping dc conductivity. In pure material the plateau is independent of frequency (4 GHz, 10 GHz. and 22 GHz), but in the temperature range above 135 K strong frequency dependence is observed. Iodine doping causes frequency dependence also in the plateau range. Particular doping rates give rise to several conductivity behaviors for different crystal directions. The results are discussed referring to CDW depinning and relaxation processes.