研究・研究者
研究会・セミナー
| 演 題 | 「Synthesis peculiarities and properties of radical cation salts k-(BEDT-TTF)2Cu[N(CN)2]X」 |
|---|---|
| 日 時 | 2005年10月06日(木) 16:00 |
| 講演者 | Dr. Natalia D. Kushch Institute of Problems of Chemical Physics, Russia Academy of Sciences |
| 場 所 | 研究棟201セミナー室 |
| 概 要 | Isostructural radical cation salts of the k-(BEDT-TTF)2Cu[N(CN)2]X family, where BEDT-TTF is an organic pi-donor, bis (ethylenedithio) tetratuiafulvalene, Hal=Cl, Br, I and their mixtures, have been intensely studied over the last years. They demonstrate a wide variety of the electron properties despite of their similar crystal structures. These compounds are layered materials built of conducting radical cation BEDT-TTF layers which alternate with the layers of Cu[N(CN)2]X- anions. The anion sheets consist of polymeric zig-zag chains extended along the a-direction, which involve a flat three-coordinated Cu+ ion with two bridged (NC)N(CN) groups and the terminal halogen X atom. The radical cation layer is formed by pairs of the BEDT-TTF molecules, which are packed perpendicular to each other in the crystal. According to the theoretical calculations of the band structure these materials are expected to be metals. It was found that the radical cation salts with X=Br, Br0.5Cl0.5 and Br0.7Cl0.3 are ambient pressure organic superconductors with Tc =11.6 K, while the salts with X=Cl and Br0.9I0.1 undergo a superconducting transition at 0.3 kbar with Tc=12.8 K and 3.5 K, respectively. A salt with X=I exhibits a superconducting transition at 1.2 kbar with Tc=8 K.
Recently we prepared the single crystals of the new k'-(BEDT-TTF)2Cu[N(CN)2]Cl(k'-Cl) salt, which in contrast to the known Mott insulator k-(BEDT-TTF)2Cu[N(CN)2]Cl show metallic properties and undergo a superconducting transition at 11.5 K at ambient pressure. An X-ray analysis of these crystals revealed some distinctions in structure of k'-Cl as compared to the usual Cl: the smaller size of the unit cell (chemical compression), deficiency (6%) of the occupancy of the Cu position and different ratio of the staggered to eclipsed ethylene conformations. The conformational state of the BEDT-TTFs, as determined by the populations of the eclipsed and staggered conformations of the ethylene groups, are disordered at room temperature and tend towards eclipsed order on cooling. |
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