The electrical conductivity of dry polycrystalline olivine compacts at high temperatures and pressures

摘要

The electrical conductivity of dry polycrystalline olivine compacts (hot-pressed and sintered pellets) was measured at pressures of 1.0-4.0 GPa, at temperatures of 1073-1423 K, and at different oxygen fugacities via the use of a YJ-3000t multi-anvil press. Oxygen fugacity was controlled successfully by means of five solid buffers: Fe_3O_4-Fe_2O_3, Ni-NiO, Fe-Fe_3O_4, Fe-FeO and Mo-MoO_2. Within the selected frequency range of 10~2-10~6 Hz, the experimental results indicate that the grain interior conduction mechanism is characterized by a semi-circular curve on an impedance diagram. As a function of increasing pressure, the electrical conductivity of polycrystalline olivine compacts decreases, whereas the activation enthalpy and the temperature-independent pre-exponential factors increase slightly. The activation energy and activation volume of polycrystalline olivine compacts were determined to be 141.02±2.53 kJ/mol and 0.25±0.05 cm~3/mol, respectively. At a pressure of 4.0 GPa, electrical conductivity was observed to increase as a function of increasing oxygen fugacity, and the relationship between electrical conductivity and oxygen fugacity can be described as log_(10) (σ) = (2.47±0.085) + (0.096±0.023)×log_(10) f_(O_2)+ (-0.55±0.011)/T, which presents the exponential factor q (～0.096). Our observations demonstrate that the primary conduction mechanism for polycrystalline olivine compacts is a small polaron.