ELSEVIER Synthetic Metals 94 ( 1998) 3 l-34 Surface-conductive polymer composites based on (BEDT-TTF) &u( SCN) 2 J.K. Jeszka a,b,* , A. Sroczyfiska a, A. Tracz a, H. Miiller ’ ‘Center of Molecular and Macromoiecular Studies, Polish Academy of Sciences, 90-363 Mdf, Poland h Institute of Polymers, Technical Univemity of Lddt 90-924 tidt Poland ‘European Synchrotron Radiation Facility, F-38043 Grenoble, France Abstract Methods of preparation and studies of the properties of the first polymer composites using (BEDT-TTF),Cu(SCN), (BEDT- TTF= bis(ethylenedithio)tetrathiafulvalene) as a conductive phase are reported. It is shown that a networkof a conductive (BEDT- TTF) &u( SCN) Z salt can be obtained. However, besides superconducting K -( BEDT-TTF) &u( SCN) 2 atleast two other salts which comprise Cu(SCN),- are known: a-phase and (BEDT-TTF)Cu,( SCN)3. Scanning electron microscopy (SEM) micrographs and X-ray diffracto- grams have shown that,although by chemical oxidation the K-phase is usually obtained, in the composite films the additive crystallization leads mostly to (w-( BEDT-TTF),Cu( SCN),. 0 1998 Elsevier Science S.A. All rights reserved. Keywords: Polycrystalline thin films; Phase-segregated composite interfaces; Organic superconductors; Semiconducting films; Solution processing; X-ray diffraction 1. Introduction Among more than 20 organic superconductors based on bis( ethylenedithio) tctrathiafulvalenc (BEDT-TTF) , K- (BEDT-‘TTF),Cu( SCN), has an exceptionally high T, of 10.4 K [ I] which makesit one of the most attractive candi- dates for potential applications. However, as long as only milligram amountsof tiny crystals could be obtained by a tedious electrocrystallization process, possibilities of appli- cations were very limited. Recently, it hasbeenshown that K-( BEDT-TTF) &u( SCN) 2 can also be obtained by non- electrochemical methods[ 21. This opens the way also to the preparation of superconductive polymer composites based on this salt, particularly via formation of conductive networks by in situ crystallization (reticulate doping) [ 3,4]. Although superconductivity was not observed[ 51 in pressed pellets of K-(BEDT-TTF),Cu( SCN),, suchpolymer composites can exhibit electrical propertiesmore similar to thoseof single crystals than thoseof pressed pellets and evaporated layers [ 61 including the onset of superconductivity [7]. The previously developedmethod of preparation of con- ducting films with BEDT-TTF salts by simultaneous poly- mer swelling and oxidation of BEDT-TTF with IZ or BrZ [4,8] cannot be applied in the case of K-( BEDT- * Corresponding author. 0379-6779/98/$19.00 0 1998 Elsevier Science S.A. All rights reserved. PIISO379-6779(97)04135-O TTF),Cu( SCN)P. This method involves vapor treatment while Cu(SCN), is non-volatile and its solubility in most solventsis very low. Therefore, it was necessary to develop new routes for the preparation of suchcomposites. In the present communication we report on the preparation andproperties of the first polymer composites using(BEDT- TTF),Cu( SCN), as a conductive phase. However, besides superconducting K-(BEDT-TTF),Cu( SCN),, at least two other salts which comprise Cu( SCN),- areknown: a-phase which undergoes metal-insulator transition around 200 K [91 and (BEDT-TTF) CuZ( SCN) 3 [ IO]. It is shownthat in spite of formation of K-phase by chemicaloxidation [ 21, in the obtainedfilms the additive crystallization leads mostly to a-(BEDT-TTF)&u(SCN)~. 2. Experimental Reagent grade BEDT-TTF and the solvents (Fluka) were used asreceived. Poly( bisphenol-A-carbonate) (PC, b!l, = 35 000) was purchased from Goodfellow. Cu(SCN), was synthesizedaccording to the literature procedure [ 21. The PC films which contained2 wt.% of molecularly dispersed BEDT-TTF were castfrom a-dichlorobenzene at 120°C and used as startingmaterial.