Experimental study of grain boundary electrical conductivities of dry synthetic peridotite under high-temperature, high-pressure, and different oxygen fugacity conditions

At pressures of 1.0-4.0 GPa and temperatures of 1073-1423 K and under controlled oxygen fugacity (Fe3O4 + Fe2O3, Ni + NiO, Fe + Fe3O4, Fe + FeO and Mo + MoO2 buffers), the grain boundary conductivity of dry synthetic peridotite was measured using the YJ-3000t multianvil press. Within the frequency range from 10(-2) to 10(6) Hz, there exist two impedance arcs representing conductive mechanisms of the grain interior and grain boundary of the sample. The resistances of the grain interior and grain boundary mechanisms add in a serial manner. The experimental results indicate that the grain boundary conductivity (sigma(gb)) increases with increasing temperature ( T), and the relationship between log sigma(gb) and 1/T conforms to the Arrhenius relation. With the rise of pressure, the grain boundary conductivity increases, and the activation enthalpy increases accordingly. The activation energy and activation volume of grain boundary charge carriers have been determined, and they are 1.28 +/- 0.01 eV and 0.45 +/- 0.05 cm 3 mol(-1), respectively. We also found that the grain boundary conductivity increases with increasing oxygen fugacity at constant pressure and temperature. Furthermore, the small polaron conduction mechanism of the grain interior and the segregation effect of the grain boundary can provide reasonable explanations for the behavior of grain boundary conductivity of dry synthetic peridotite at high pressure.