Experimental Study on the Electrical Conductivity of Orthopyroxene at High Temperature and High Pressure under Different Oxygen Fugacities

Abstract

Abstract At presure 1.0–4.0 GPa and temperature 1073–1423 K and under oxygen partial pressure conditions, a YJ‐3000t multi‐anvil solid high‐pressure apparatus and Sarltron‐1260 Impedance/Gain‐Phase analyzer were employed to conduct an in‐situ measurement of the electrical conductivity of orthopyroxene. The buffering reagents consist of Ni+NiO, Fe+Fe3O4, Fe+FeO and Mo+MoO2 in order to control the environmental oxygen fugacity. Experimental results made clear that: (1) within the measuring frequency range from 10−1 to 106 Hz, the complex impedance (R) is of intensive dependence on the frequency; (2) The electrical conductivity (σ) tends to increase along to the rise of temperature (T), and Log σ vs. 1/T fit the Arrenhius linear relations; (3) Under the control of oxygen buffer Fe+Fe3O4> with the rise of pressure, the activation enthalpy tends to increase whereas the electrical conductivity tends to decrease. The activation energy and activation volume of the main current carriers of orthopyroxene have been obtained, which are (1.715±0.035) eV and (0.03±0.01) cm3/mol, respectively; (4) Under given pressure and temperature, the electrical conductivity tends to increase with increasing oxygen fugacity, while under given pressure the activation enthalpy tends to decrease with increasing oxygen fugacity; and (5) The sample's small polarons mechanism has provided a reasonable explanations to the conduction behavior at high temperature and high pressure.