PREPARATION AND CHARACTERIZATION OF CPP2I3-DELTA SINGLE-CRYSTALS

CPP2I3-delta single crystals (where CPP = 1, 2, 7, 8 - tetrahydrodicyc lopenta-(cd-lm)-perylene ) were prepared by diffusion and by electrocr ystallisation techniques. By diffusion, only thin needles were obtaine d, while the galvanostatic process gives, in addition, diamond shaped crystals. X-ray diffraction studies on a diamond shaped crystal reveal ed a stoichiometry CPP2(I3)0.89, while the CHN microanalysis for thin needles gives delta values from -0.1 to 0.4, in different batches. Thi n needles are characterized by higher electrical conductivity, sigma(R T) almost-equal-to 200 OMEGA-lcm-1, and thermopower, S(RT) almost-equa l-to 30muV/K, while the diamond shaped crystals have sigma(RT) almost- equal-to 0.5 OMEGA-lcm-1 and S(RT) almost-equal-to - 8muV/K. In all ca ses both electrical resistivity and thermopower show metallic behaviou r at high temperatures down to almost-equal-to 60 K, where a metal-ins ulator transition occurs. EPR shows an almost isotropic line (g-2.0044 ) with width of almost-equal-to 6 G, at room temperature, without sign ificant differences for the two different types of crystals. The thin needles magnetic susceptibility shows an almost temperature independen t contribution above the metal to insulator transition, ascribed to th e conduction electrons in the CPP chains.