Experimental study on the electrical properties of carbonaceous slate: a special natural rock with unusually high conductivity at high temperatures and pressures

The electrical conductivities of carbonaceous slate were measured using a complex impedance spectroscopic technique at 0.5−1.5 GPa and 423−973 K in the frequency range of 10-1 to 3.5×106 Hz. Experimental results indicate that the conductivities of carbonaceous slate slightly increased with increasing temperatures and pressures, respectively. At a certain temperature range, the conductivities of carbonaceous slate follow an Arrhenius relation. There are three Arrhenius relations for the conductivities of carbonaceous slate at a certain pressure. From high temperature range to low temperature range, the activation enthalpies for the conductivities of carbonaceous slate are found to be 0.02‒0.03 eV, 0.05‒0.06 eV, and 0.11‒0.13 eV, respectively. Electron conduction is proposed to be the conduction mechanism for carbonaceous slate at high temperatures and pressures. It is suggested that the unusually high conductivities of carbonaceous slate (0.1‒1 S/m) are associated to interconnected amorphous carbon. Furthermore, the electrical conductivities of carbonaceous rocks can be used to interpret the high-conductivity layers (HCLs) in the Earth’s interior.