ac calorimetry and EPR study on metal-insulator transition and glass transition in an organic conductor with double-column structure, (DIMET)(2)BF4

Successive metal-insulator transitions in (DIMET)(2)BF4 were studied by cho pped-light ac calorimetry and electron paramagnetic resonance (EPR) measure ment. All anomaly due to the metal-insulator transitions has been clearly d etected in ac calorimetry between 20 and 35 K. In contrast to other double- column salts (DMET)(2)BF4 and (DMET)(2)ClO4, successive metal-insulator tra nsitions detected in transport properties are shown to be thermodynamic pha se transitions. The EPR detected an anomaly only for the lowest transition around 12 K. The properties of the metal-insulator transitions are compared among the DIMET and DMET salts having the double-column structure. A frequ ency-dependent step in heat capacity was detected around 110 K. The step-li ke anomaly is attributed to a glass transition due to freezing of the intra molecular motion of the ethylene group in the ET moiety within a DIMET mole cule.