Browsing by Author "Bender, Klaus"

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    α- and β-(BEDT-TTF)2+I3-: two dimensional organic metals
    (1985) Hennig, Ingolf; Bender, Klaus; Schweitzer, Dieter; Dietz, Klaus; Endres, Helmut; Keller, Heimo J.; Gleitz, Arno; Helberg, Hans W.
    Electronic properties of α- and β-(BEDT-TTF)2I3 crystals are reported.
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    (BEDT-TTF)2+J3- : a two-dimensional organic metal
    (1984) Bender, Klaus; Dietz, Klaus; Endres, Helmut; Helberg, Hans W.; Hennig, Ingolf; Keller, Heimo J.; Schäfer, Herbert; Schweitzer, Dieter
    Temperature-dependent thermopower-, dc- and microwave-conductivity measurements on the two-dimensional organic metal (BEDT-TTF)2+J3- are reported.
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    Electric conductivity and thermoelectric power of various polypyrroles
    (1987) Bender, Klaus; Gogu, Emil; Hennig, Ingolf; Schweitzer, Dieter; Münstedt, Helmut
    The dc-conductivity and thermoelectric power of electrochemically prepared polypyrroles have been investigated in the temperature range between 300 K and 1.3 K on unaged, aged (24-120 days at 80°C in air) and chemically modified samples. The linear temperature dependence of the thermopower of unaged polypyrroles demonstrates clearly the contribution of metallic regions to the electronic transport properties. The temperature dependence of the conductivity of the polypyrroles investigated corresponds to that predicted by the variable range hopping model.
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    Electric conductivity and thermopower of quasi one-dimensional (perylene)2(AsF6)0.75(PF6)0.35•0.85CH2Cl2 crystals
    (1983) Bender, Klaus; Schweitzer, Dieter; Keller, Heimo J.
    The temperature dependence of the conductivity parallel and perpendicular to the stack axis as well as of the thermopower S of (pe)2(AsF6)0.75(PF6)0.35.0.BSCH2Cl2 crystals is reported.
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    Magnetic susceptibility under pressure and anisotropy of electrical conductivity in quasi-one-dimensional (perylene)2(AsF 6)0.75(PF6)0.35 × 0.85CH2Cl2
    (1983) Moritz, I.; Shaheen, Salem A.; Hardebusch, U.; Schilling, James S.; Weger, Meir; Bender, Klaus; Schweitzer, Dieter; Keller, Heimo J.
    The magnetic susceptibility and electrical conductivity of the quasi-one-dimensional organic metal (Perylene)2(AsF6)0.75(PF6)0.35 × 0.85CH2Cl2 was studied in the temperature range 3–300 K. The measured susceptibility can be separated into its defect χd, core χc and enhanced paramagnetic spin susceptibility χp components. χp is found to decrease upon lowering the temperature or applying pressure, in analogy with results on charge transfer compounds such as TTF-TCNQ. The conductivity ratio σdouble vertical bar/σperpendicular also decreases with falling temperature. The present results are discussed within the context of a model which takes into account band-narrowing (electron localization) due to strong electron-phonon coupling.
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    Organic metals from simple aromatic hydrocarbons: perylene radical salts
    (1985) Schweitzer, Dieter; Hennig, Ingolf; Bender, Klaus; Endres, Helmut; Keller, Heimo J.
    Crystal structures, temperature dependent thermopower and conductivity measurements of several metallic perylene radical salt phases are discussed.
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    Preparation, structure and investigations of BEDT-TTF trihalides
    (1985) Endres, Helmut; Hiller, M.; Keller, Heimo J.; Bender, Klaus; Gogu, Emil; Heinen, Ilsabe; Schweitzer, Dieter
    Crystals of the β-phases of (BEDT-TTF)2Br-I-Br (1) and (BEDT-TTF)2I-I-Br (2) have been isolated by electrocrystallization. The solids can be obtained using different tetrabutylammonium trihalides containing iodine and bromine as supponing electrolytes. Cyclovoltammetric results show clearly that the trihalide anions are involved in the oxidation reactions near the anode which finally lead to the crystals.
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    Preparation, structure and physical properties of BEDT-TTF nitrates
    (1985) Weber, Angelika; Endres, Helmut; Keller, Heimo J.; Gogu, Emil; Heinen, Ilsabe; Bender, Klaus; Schweitzer, Dieter
    Electrocrystallization of BEDT-TIF in THF with tetrabutylammonium nitrate as supporting electrolyte leads to the deposition of at least three different phases. Sheets of BEDT-TTF radical cations with short intermolecular S···S contacts (>3.315(4) A) are separated by anion layers. Two more BEDT-TrF nitrates have been characterized by their unit cell data. Resuhs of temperature dependent electrical conductivity and thermopower measurements on crystals of the a-phase are presented. They are metallic down to about 30 K.
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    Radical cation salts of an unsymmetrical BEDT-TTF derivative: DIMET
    (1987) Bender, Klaus; Endres, Helmut; Gärtner, Stephan; Gogu, Emil; Heid, Rolf; Heinen, Ilsabe; Keller, Heimo J.; Kraatz, Andrea; Schweitzer, Dieter
    A surprising fact in the structures of the organic superconductors (TMTSF)2 Cl04 and -β-(BEDT-TTF)2X (X=I3-, IBr2- and AuI2-) is that there exists a slight dimerisation of the donor molecules within the stacks of these radical cation salts. Therefore, the question arises whether a more pronounced dimerisation in organic radical salts of this type leads to stronger intra- and interstack interactions and to stronger couplings between the unpaired electrons. This might result in an increase of the transition temperature to superconductivity. A step in this direction is the preparation of "unsymmetrical" donors like DIMET, which was synthesized recently. This new donor was electrocrystallized by us in different solvents using tetrabutylammonium salts of various anions like ClO4-, ReO4-, NO3-, I3-, (AuI2)-, PF6-, ASF6- and SbF6- as electrolytes. With all these anions radical salts were obtained and in some cases even several crystallographic different phases.
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    Radical cation salts of an unsymmetrical BEDT-TTF derivative: molecular structure and physical properties of (DIMET)2ClO4xTHF
    (1985) Heid, Rolf; Endres, Helmut; Keller, Heimo J.; Gogu, Emil; Heinen, Ilsabe; Bender, Klaus; Schweitzer, Dieter
    Sheets of cations with an average charge of 1/2+ are separated by sheets of anions and THF solvent molecules. Intermolecular S···S contacts result in two-dimensional physical properties. Electrical conductivity and thermopower measurements indicate two broad phase transitions at around 200 K and 80 K.
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    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.
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    Synthesis, structure and physical properties of a two-dimensional organic metal, di[bis(ethylenedithiolo)tetrathiofulvalene] triiodide, (BEDT-TTF)2+I3-
    (1984) Bender, Klaus; Hennig, Ingolf; Schweitzer, Dieter; Dietz, Klaus; Endres, Helmut; Keller, Heimo J.
    Electrical oxidation of bis(ethylenedithiolo)tetrathiofulvalene (BEDT-TTF) 1 in a nitrogen saturated tetrahydrofurane solution containing (n-C4H10)4N+I3 as electrolyte results in the deposition of crystal plates of (BEDT-TTF)+2I3 (C10H8S8)2I3. These two dimensional crystals are triclinic, space group P1, a = 9.211(2), b=10.850(4), c = 17.488(5) Aring, agr=96.95(2), β = 97.97(2), γ = 90.75(2)°, V = 1717 Aring3, Mr = 1150.01, Z=2, Dx =2.22 g cm-3. Rw = 0.037 for 2462 observed reflections. Sheets of alternating cations and anions occur in the compound. The most prominent intermolecular S-S contacts (∼3.5Aring) are found between the stacks of BEDT-TTF. The stacking of the molecules and the interstack contacts give the compound a two-dimensional character which influences the physical properties.
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    Temperature and pressure dependence of the resistivity of β-(BEDT-TTF)2X (X=I3, I2Au) and αt-(BEDT-TTF)2I3
    (1988) Weger, Meir; Bender, Klaus; Klutz, Thomas; Schweitzer, Dieter; Gross, Frieder; Heidmann, Claus Peter; Probst, Christian; Andres, Klaus
    The temperature dependence of the resistivity of the organic metals and superconductors {β-(BEDT-TTF)2I3, β-{3-(BEDT-TTF)2I2Au and αt(BEDT-TTF)2I3 was measured at ambient and at several isotropic pressures (up to 2.5 kbar). By the application of a relatively low pressure, it is possible to measure the term in the resistivity that is linear in temperature. This term is masked by the larger T2 term at ambient pressure. It is shown that in the temperature range below 120 K, the external modes are mainly responsible for the resistivity, while above this temperature the flipping of the CH2 groups becomes important. The linear electron-phonon coupling corresponds to a value of λ between 1 and 1.5.