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

Electrical conductivities of pyroxenite were measured between frequencies of 10(-1) and 10(6) 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 degrees C) and the pressure from 1.0 to 4.0 GPa. We observe that: (1) the electrical conductivity (sigma) of pyroxenite depends on frequency; (2) s tends to increase with rising temperature (T), and Log s and 1/T obey a linear Arrhenius relationship; (3) under control of the buffer Fe + Fe3O4, s 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) cm(3)/mol, respectively; (4) for a given pressure and temperature, s 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.