Experimental measurement of the electrical conductivity of pyroxenite at high temperature and high pressure under different oxygen fugacities

Abstract

Electrical conductivities of pyroxenite were measured between frequencies of 10⁻¹ and 10⁶ Hz in a multi-anvil pressure apparatus using different solid buffers (Ni+NiO, Fe+Fe₃O₄, Fe+FeO and Mo+MoO₂) to stabilize the partial pressure of oxygen. The temperature ranged from 1073 to 1423 K (800 to 1200 °C) and the pressure from 1.0 to 4.0 GPa. We observe that: (1) the electrical conductivity (σ) of pyroxenite depends on frequency; (2) σ tends to increase with rising temperature (T), and Log σ and 1/T obey a linear Arrhenius relationship; (3) under control of the buffer Fe+Fe₃O₄, σ tends to decrease with rising pressure, nevertheless the activation enthalpy tends to increase. For the first time we have obtained values for the activation energy and activation bulk volume of the main charge carriers, which are (1.60±0.07) eV and (0.05±0.03) cm³/mol, respectively; (4) for a given pressure and temperature, σ tends to rise with increased oxygen fugacity, whereas the activation enthalpy and preexponential factor tend to decrease; and (5) the behaviour of the electrical conductivity at high temperature and high pressure can be reasonably interpreted by assuming that small polarons provide the dominant conduction mechanism in the pyroxenite samples.

Keywords:

• Pyroxenite
• High temperature and high pressure
• Electrical conductivity
• Oxygen fugacity
• Small polaron

Acknowledgements

We thank the anonymous reviewer for his very helpful comments and suggestions in the reviewing process. This research is financially supported by CAS Knowledge-Innovation Key Orientation Project (Grant No. KZCX3- SW-124), the National Natural Science Foundation of China (Grant No. 40573046 and 49674221), and CAS One- Hundred Talented Personnel Program.