Origin of the resistivity anomalies of (EDT–TTF)[M(dmit)2](M = Ni, Pd)

Abstract

α-(EDT–TTF)[Ni(dmit)₂] comprises crossing columns of EDT–TTF and Ni(dmit)₂ and exhibits unique metallic behaviour with a characteristic resistivity peak at around 14 K. The possibility of the development of the superstructure was examined down to 9 K by using a low-temperature imaging plate X-ray system, but no extra X-ray reflections could be found below 14 K. The 14 K anomaly is, therefore, thought not to originate from charge density wave (CDW) instability. New phases of γ-(EDT–TTF)[Pd(dmit)₂] and γ-(EDT–TTF)[Ni(dmit)₂] were found. γ-(EDT–TTF)[Pd(dmit)₂] has parallel columns of EDT–TTF and Pd(dmit)₂ and shows a resistivity anomaly around 80 K. Below 80 K, X-ray satellite reflections indicating CDW formation were observed. γ-(EDT–TTF)[Ni(dmit)₂] undergoes a metal–insulator transition at around 100 K.