J. Phys. IV France 114 (2004) 463
DOI: 10.1051/jp4:2004114108

New ambient pressure organic superconductor with T_c= 8.1  K: (EDT-TTF)4Hg I ₈

R.N. Lyubovskaya^{1, 1}, E.I. Zhilyaeva¹, S.A. Torunova¹, G.A. Mousdis², G.C. Papavassiliou², J.A.A.J. Perenboom³, Pesotskii^{1, 3, 4} and R.B. Lyubovskii<sup>1, 3, 4

1</sup>  Institute of Problems of Chemical Physics RAS, Chernogolovka, MD 142432, Russia
²  Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Athens 11635, Greece
³  Nijmegen High Field Magnet Laboratory, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands
⁴  International Laboratory of High Magnetic Fields and Low Temperatures, Wroclaw 53-529, Poland

Abstract
New ethylenedithiotetrathiafulvalene (EDT-TTF)-based radical cation salts with mercury containing anions of different size and shape have been isolated and studied. Among these compounds the new ambient pressure organic superconductor (EDT-TTF) ₄Hg I ₈, 0.1 0.2, with T _c=8.1K has been synthesized. Depending on a EDT-TTF/HgI ₃^-/HgI ₂ ratio, electrochemical crystallization of EDT-TTF affords either hexagonal (EDT-TTF) ₄Hg I ₈, ( 0.1 0.2) or rectangular (EDT-TTF) ₂HgI ₃ crystals. Three types of hexagonal crystals were certified using conductivity measurements: the crystals with superconducting temperature T _c=8.1K under ambient pressure (1), those undergoing a superconducting transition at 5 <T _c<8K under p 0.3 kbar (2), and the crystals undergoing a metal-insulator transition below 35K (3). Key words. Organic superconductors, transport measurements, conductivity

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