Electrical resistivity of a novel oxadiazole derivative as a function of pressure and temperature using a diamond anvil cell

The in-situ electrical resistance measurement on the microcrystal of 1,4-bis[(4-methyloxyphenyl)-1,3,4-oxadiazolyl]2,5-bisheptyloxyphenylene (OXD-2) has been carried out under conditions of high pressure and temperatures higher than room temperature by using the diamond anvil cell (DAC). The sample's resistivity was calculated with a finite element analysis method. The temperature and pressure dependencies of the resistivity of OXD-2 microcrystal were measured up to 150 degrees C and 16GPa. The resistivity of OXD-2 decreases with increasing temperature, indicating that OXD-2 exhibits organic-semiconductor conducting property in the region of experimental pressure. Between 90-100 degrees C, the resistivity drops with the temperature, which reveals a temperature-induced phase transition. As the pressure increases, the resistivity of OXD-2 increases and reaches a maximum at about 6 GPa, and then begins to decrease at higher pressures. Combining the in-situ x-ray diffraction data with the resistivity measurement under pressure, the anomaly resistivity drop after 6 GPa is confirmed to be due to the pressure-induced amorphous phase transition of OXD-2.