METAL-INSULATOR TRANSITIONS IN PRESSED PELLETS OF BF4- DOPED POLY(3-METHYLTHIOPHENE)

From Electron Spin Resonance (ESR) data in pressed pellets of BF4- dop ed Poly(3-methylthiophene) (P3MT) we obtained simultaneously the param agnetic susceptibility and the microwave conductivity. We observed a t ransition from a high-temperature insulator state to a room-temperatur e metallic state. Around 240K evidence of a Peierls transition is obse rved, but if the sample is slowly cooled, this transition is partially suppressed. DC conductivity data taken with the sample quenched to 79 K show a non-linear I-V response for very small electric fields, sugge sting depinning of Charge-Density Wave (CDW). The data for heating and cooling the system above room temperature, indicate the formation of bipolarons.