Resistivity measurements on TMTTeN and [Ni(ptdt)2] above 20 GPa and electrical and structural studies on [Au(tmdt)2]

Abstract The four-probe resistivity measurements were performed on the molecular crystals of TMTTeN (=tetramethyltetratelluronaphthalene) and [Ni(ptdt) 2 ] (ptdt=propylenedithio tetrathiafulvalenedithiolate) by using a diamond anvil cell (DAC) up to 30 and 21 GPa, respectively. In spite of extremely large enhancement of room-temperature conductivity (∼350 Scm −1 at 25.4 GPa) and metallic behavior at low temperatures (25–65 K at 25.4 GPa), the pressure-induced metallic state could not be observed in TMTTeN up to 30 GPa at least around room temperature. The resistivity of [Ni(ptdt) 2 ] decreased with increasing pressure and became approximately 10 −2  Ω cm at 18 Gpa. The temperature dependence of the resistivity exhibited a weakly semiconducting behavior. At around 19.5 GPa, [Ni(ptdt) 2 ] showed weakly metallic behavior down to low temperature. However, this pressure-induced metallic state was not stable. At 20.7 GPa, the resistivity increased again below 40 K. The four-probe resistance measurements were also performed on the extremely brittle thin-plate microcrystals of single-component antiferromagnetic molecular conductor [Au(tmdt) 2 ]. The resistance ( R ) decreased continuously with decreasing temperature ( T ). Except for a slight bending of the R−T curve at around the magnetic transition temperature ( T N =110 K), no resistance anomaly was observed. Nonetheless, the existence of the metallic state below T N was confirmed for the first time from the results of single-crystal resistance measurement. The precise crystal structure examinations were performed on [Au(tmdt) 2 ] by the powder X-ray diffraction data at the temperature range of 9–300 K.