Preparation of molecular crystals containing metal elements and their electrical and magnetic properties

点击翻译按钮获取中文摘要

The pressure effect on the electrical resistance of the molecular conductor α-Et_2Me_2N[Ni(dmit)_2]_2 has been studied. This salt is a molecular metal down to 0.5 K, although the resistance jump due to the order-disorder phase transition of Et_2Me_2N^+ is observed at 250 K. This structural phase transition is so drastic as to damage crystals and to detach electrical contacts from a crystal. To avoid that, gold wires were attached on a crystal with a conductive silver epoxy adhesive. Then, the system has been designed and constructed, which enables to cool samples slowly and to pressurise sample gently and continuously. With applying the pressure at room temperature, the resistance dropped suddenly in the pressure range between 0.11 GPa and 0.19 GPa. At ambient pressure, the drastic resistance jump happened at 250 K. However, this resistance jump disappeared under pressures and instead, the small anomalies at 280 K under 0.17 GPa and 304 K under 0.28 GPa were observed. These results were plotted on the temperature-pressure phase diagram. It is noted that all four points are on the one line. This phase diagram shows that the temperature of the phase transition increases from 250 K to room temperature at the rate of ca. 20 K / 0.1 GPa as applying the pressure. This phase transition is also observed as an anomaly on the magnetic susceptibility at 250 K. We shall perform the measurements of magnetic susceptibilities under pressure by use of a SQUID magnetmeter and complete the phase diagram from the results.Crystals of (BEDT-TTF)_x[Pd(ox)_2] (ox=oxalate), 2, 6-pyridine-bis (nitronyl nitroxide) and its Zn and Cu salts were prepared ; their electrical and magnetic properties were examined.