Metastable state of. beta. -(BEDT-TTF)/sub 2/I/sub 3/ with a superconducting transition temperature of 7. 5 K

The high-temperature superconducting phase with T/sub c/ = 7.5 K, which arises in ..beta..-(BEDT-TTF)/sub 2/I/sub 3/ crystals when subjected to pressure, is shown to be metastable. The observed value of T/sub c/ is apparently the highest value for this high-temperature superconducting phase in ..beta..-(BEDT-TTF)/sub 2/I/sub 3/ samples synthesized by chemical oxidation.