No abstract

We confirm the observation of superconductivity at ambient pressure above 10 K in the organic metal (BEDT-TTF}2Cu(SCN) 2 as reported recently by Urayama et al [12]. In addition we have measured ESR, ac-susceptibillty and thermopower in crystals of (BEDT-TTF )2Cu (SCN)2 and have shown that in contrast to other organic superconductors here a relatively sharp superconducting transition even in the ac-susceptibility can be observed which saturates already around 8 K. The thermopower measurements indicate a clear metal-metal phase transition at 100 K and a possible second phase transition at around 50 K, while from the temperature dependence of the resistivity and susceptibility (ESR) these phase transitions cannot be observed.Since the observation of superconductivity at temperatures up to 100 K in the high T c ceramic Cu-oxides -first discovered by Bednorz and MUller [ I ] -superconductivity has attracted again a lot of interest. Compared to the high T c anorganlc superconductors the transition temperatures into a superconducting state in organic materials is still rather low. Nevertheless, the development of new superconductors in this class of materials is quite fast. Since the first observation of superconductivity in an organic metal -

The dc-conductivity and thermoelectric pover of electrochemically prepared polypyrroles have been investigated in the temperature range between 300 K and 1.3 K on unaged. aged ( 2~-120 days at 80 0 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 ot the polypyrroles investigated corresponds to that predicted by the variable range hopping model.

We report bulk superconductivity at ambient pressure in polycrystalline pressed samples of ~t-(BEDT-TTF)213. As in single crystals of ~t-(BEDT-TTF)21a the onset for superconductivity in the polycrystalline pressed samples lies at about 9K but the transition is broader. Zero resistivity is observed at 2.2 K and the middle of the transition is found at 5K. The measurement of the ac susceptibility shows that at 2K about $0g of the sample is superconducting, but at this temperature the transition is still not saturated. The observation of bulk superconductivity in this polycrystalline pressed samples is of special interest because it demonstrates that organic superconductors can be used in principle as well for the production of electronic devices such as squids and superconducting cables. In addition the finding of bulk superconductivity in large pressed samples of crystallites of the typical diameter of lttm of an organic metal indicates that the observation of superconductivity in organic polymers should be possible as well.Recently bulk superconductivity at 8K and ambient pressure was reported in single crystals of the quasi two dimensional organic metal ~t-( BEDT-TTF )2 I3 [1]. From measurements of the upper critical fields Hc2 and using an anisotropic effective mass mode) in the picture of the Ginzburg Landau theory the coherence lengths at 0 K of ~j.= 22 A, ~ II = 120 A and the penetration depths of ~L= 7SOA, ~,= 4300A were obtained [2]. These results led to the idea that, similar to the high temperature superconductors of the metal oxides, it should be possible to obtain bulk superconductivity in polycrystalline pressed samples of ~t -( BEDT -TTF) 213. The remarkable fact of such finding would be that in such a case organic superconductors in principle could be used as well for the preparation of electronic devices such as squids and might even be suitable for the preparation of superconducting cables. Such a finding would further be an indication that superconductivity should be observable as well in organic polymers. Samples of the size 4xlx0.Smm were prepared from grained single crystals (the resulting crystallites from the graining process had typical diameters of 0.S -10 ttm) of the organic metal ~-(BHDT-TTF)2I 3 [3,4] by applying a pressure of (3-10). 103 kg/cm 2 to the powder. These mechanically very stable samples were tempered at 7S°C for S0 hours in order to obtain samples of ~,t-(BEDT-TTF)2I 3 [1]. The conductivity was measured with the usual four point method,

Crystals of (BEOT-TTF),Cu(NCS)l were prepared by seyeral methods and the aupe,... 13 C Knight sblfu meuured by magic anale aample splnninI and NMR Cf08S polarlaaUon methods .uppon the picture of the layered superconductor.