Anisotropy of electrical conductivity in dry olivine

The electrical conductivity (sigma) was measured for a single crystal of San Carlos olivine (Fo(89.1)) for all three principal orientations over oxygen fugacities 10(-7) < f(O2) < 10(1) Pa at 1100, 1200, and 1300 degrees C. Fe-doped Pt electrodes were used in conjunction with a conservative range of f(O2), T, and time to reduce Fe loss resulting in data that is similar to 0.15 log units higher in conductivity than previous studies. At 1200 degrees C and f(O2) = 10(-1) Pa, sigma([100]) = 10(-2.27) S/m, sigma([010]) = 10(-2.49) S/m, sigma([001]) = 10(-2.40) S/m. The dependences of sigma on T and f(O2) have been simultaneously modeled with undifferentiated mixed conduction of small polarons and Mg vacancies to obtain steady-state f(O2)-independent activation energies: Ea([100]) = 0.32 eV, Ea([010]) = 0.56 eV, Ea([001]) = 0.71 eV. A single crystal of dry olivine would provide a maximum of similar to 10(0.4) S/m azimuthal s contrast for T < 1500 degrees C. The anisotropic results are combined to create an isotropic model with Ea = 0.53 eV.