Browsing by Author "Moldenhauer, Jörg"

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Open Access
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.
Open Access
FT-IR absorption spectroscopy of BEDT-TTF radical salts: charge transfer and donor-anion interaction
(1993) Moldenhauer, Jörg; Horn, Christof; Pokhodnia, Konstantin I.; Schweitzer, Dieter; Heinen, Ilsabe; Keller, Heimo J.
IR absorption spectra from various K-phases of BEDT-TTF radical cation salts as well as from α-(BEDT-TTF)2I3 are presented. From tbese spectra one special mode ν27 representing the asymmetric ring C=C stretching vibration is assigned and the dependence of its frequency from the average charge on the donor molecule is given. The investigation of the metal-insulator phase transition of α-(BEDT-TTF)2I3 at 135 K with respect to this vibrational model ν27 gives strong indication of a charge localization in at least one of the two crystallographic different stacks. Furthermore, we correlate the frequencies of the CH2 stretching modes of a variety of BEDT-TTF radical salts with the superconducting phase transition temperatures. These frequencies are evidently not charge dependent, but significantly reflect the strength of the interaction of the donor molecule with the respective anion. It could be shown that phases with a higher Tc of their superconducting transition exhibit a smaller red shift of these frequencies, i.e., a less attractive donor-anion interaction.
Open Access
FT-IR investigations of (BEDT-TTF)2I3 radical salts
(1993) Moldenhauer, Jörg; Pokhodnia, Konstantin I.; Schweitzer, Dieter; Keller, Heimo J.
Fourier transform infrared absorption spectra of structurally different phasis of the radical cation salt (BEDT-TTF)2I3 in the range of the molecular vibration of the donor are presented. The low-temperature spectra provide exact fingerprints of the different phases as long they have different unit cells. Additional differences concerning the position of ethylene group reflect themselves in the CH2-stretching vibrations. As a result, it could be shown that the ethylene groups of the αt-phase and β-phase must have a different order. Concerning the tempering of the different phases, it is shown that a least αt- and χt-(BEDT-TTF)2I3 are the same.
Open Access
FT-IR investigations of BEDO-TTF and radical salts of BEDO-TTF
(1993) Moldenhauer, Jörg; Pokhodnia, Konstantin I.; Schweitzer, Dieter; Heinen, Ilsabe; Keller, Heimo J.
We investigated powder absorption spectra of the donor BEDO-TTF and some radical salts of BEDO-TTF, which are metals even at low temperatures. After an assignment of the bands in the neutral donor we found in the radical salts different vibrational frequencies of bands correlated with C-O vibrations. These frequencies are directly related to the average charge on the donor molecule. Additionally frequencies of CH2-stretching vibrations exhibit differences, which can be ascribed to a varying strength of donor-anion interaction depending on the respective anion.
Open Access
Superconductivity in polycrystalline pressed pellets of k-(BEDT-TTF)2I3
(1993) Balthes, Eduard; Breining, Angela; Kahlich, Siegfried; Moldenhauer, Jörg; Schweitzer, Dieter; Bele, Petra; Brunner, Hermann; Heinen, Ilsabe; Nuber, Bernhard; Keller, Heimo J.
Investigations of the transport properties of single crystals and polycrystalline pressed samples of K-( BEDT-TTF)2I3 are presented. In contrast to polycrystalline pressed samples of K-(BEDT-TTF)2Cu(NCS)2 and K-(BEDT-TTF)2Cu [N(CN)2]Br those of K-(BEDT-TTF)2I3 show bulk superconductivity indicating that the loss of superconductivity in the first two types of samples is not due to the special structure of the K-phase, but probably due to a disproportionation of Cu1+ under the anisotropic pressure during the preparation of the samples. Annealing the single crystals as well as the polycrystalline pressed samples of K-(BEDT-TTF)2I3 at 75°C for a few days results in a structural transfomation with an increase in the transition temperature for superconductivity (about 8 K for the crystals). IR-spectra indicate a transfomatlon into a structure which is identical with αt-(BED-TTF)2I3 which seems to be the thermodynamically most stable phase of the several (BEDT-TTF)2I3 phases.