CH2 vibrations in radical cation salts based on the donor BEDT-TTF

Investigations of the CH2 stretch vibrations in radical cation salts based on the donor BEDT-TTF and the neutral donor itself are presented. The spectra taken by Fourier transform infrared absorption technique not only demonstrate the importance of the relationship between the possible positions of the CH2 groups in the BEDT-TIF molecule and the physical properties of the organic metal but also offer the opportunity to achieve structural information by the use of a simple method

Electric conductivity and thermopower of quasi one-dimensional (perylene)2(AsF6)0.75(PF6)0.35•0.85CH2Cl2 crystals

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

Resonance Raman investigations of the symmetric stretching mode of I3- anions in α and β phases of di-bis(ethylenedithio)tetrathiafulvalene tri-iodide

The resonance Raman spectra of I3- anions in the organic superconductor β-(BEDT-TTF)2I3 [BEDT-TTF represents bis(ethylenedithio)tetrathiafulvalene] were studied and discussed in comparison with the nonsuperconducting phase of α-(BEDT-TTF)2I3. In both modifications at low temperature a splitting of the Raman mode assigned to the symmetric stretching mode of the I3- anions was discovered. The splitting of this mode in the β-(BEDT-TTF)2I3 crystals is related to the commensurate superstructure developed below 125 K in contradiction to the α phase where the splitting is related to a crystal-field effect. It is shown that an electronic excitation of the β-phase crystals by laser light can induce a structural transformation at least in a thin layer of the surface. This transformation is observed by a disappearance of the splitting of the symmetric stretching mode. The structural change can be related to a transformation from the commensurate superstructure with a superconducting transition temperature Tc=1.3 K into a more ordered and symmetric structure which becomes superconducting at Tc=8.1 K

Raman investigations on single crystals and polycristalline pressed samples of organic superconducters

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

Magnetically modulated microwave absorption (MMMA) at low magnetic fields in (BEDT-TTF)-superconductors

We report magnetically modulated microwave absorption (MMMA) at low magnetic fields in crystals of the organic superconductors αt-(BEDT-TTF)2I3 and κ-(BEDT-TTF)2Cu(NCS)2. In both cases a strong MMMA-signal can easily be found below the critical temperature Tc. In some selected crystals series of narrow, periodically spaced lines are observed comparable to corresponding spectra of the CuO-type high Tcsuperconductors. A model developed for the HTSC's single crystals is used to interpret the results of the organic superconductors

The high-Tc superconducting state of β-(BEDT-TTF)2I3 at atmospheric pressure: bulk superconductivity and metastability

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

Proton relaxation in the organic superconductor (BEDT-TTF)2Cu(NCS)2

The origin of the nonexponentiallity of the proton spin-lattice relaxation in the organic superconductor (BEDT-TTF)2Cu(NCS)2 is clarified. In fine powders the nonexponentiallity results from localized paramagnetic centers whose concentration is nonuniform over the powder sample. In coarse grains at low temperatures it is due to finite penetration of the rf-field into the conducting grains

Microwave conductivity in polycrystalline (BEDT-TTF)2I3 material

Polycrystalline material of the &#945;-phase of (BEDT-TTF)2I3 was compressed to small samples (4-mm x 1mm, thickness 0.3 mm typically) at a pressure of 10 kbar. Annealing at 70°C yields the superconducting &#945;t-phase. Microwaves (10,2 GHz) enable the measurements of the conductivity for stepwise annealing after every annealing step in always the same sample. For annealing times 10 min all conductivity versus temperature curves are intersecting in an isosbestlc point at 190 K. This behaviour can be described by a conductivity relation for a two component system, from which was determined the volume fraction of the new grown &#945;t-phase in dependence of the annealing time. Starting annealing (annealing times < 10 min) shows another unexpected phase transformation. After 2 min annealing the conductivity at 200 K increases by more than one order of magnitude, but then decreases of further annealing (5-10 min) down to the value for the unannealed sample

New charge tranfer salts containing BEDT-TTF and structurally related transition metal complexes

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

Organic metals from simple aromatic hydrocarbons: perylene radical salts

Crystal structures, temperature dependent thermopower and conductivity measurements of several metallic perylene radical salt phases are discussed