中国科学院地球化学研究所机构知识库

Under conditions of 1.0 similar to 3.0 GPa, 973 similar to 1273 K and frequency range from 10(-2) to 10(6) Hz, the electrical conductivity of Fe-rich garnet single crystal is measured by virtue of 11-3000 t multi-anvil high-pressure apparatus and Solartron-1260 Impedance/Gain-phase Analyzer. A series of solid oxygen buffers including Fe3O4 + Fe2O3, Ni + NiO, Fe + Fe3O4, Fe + FeO and Mo + MoO2 are chosen to control oxygen fugacity. Two branches of impedance spectra are obtained in the complex impedance plane, one (10(2)-10(6) Hz) showing a semicircular arc originated from the origin in the Nyquist and Bode diagram, another small tail in the low frequency of 10(-2)-10(2) Hz. Experimental results show that with the rise of temperature (T), electrical conductivity (sigma) tends to increase, and Log sigma and 1/T satisfies the Arrhenius relation. Under control of a Ni + NiO oxygen buffer, with the rise of pressure, electrical conductivity decreases, and the pre-exponential factor also reduces, while the activation enthalpy rises, activation energy and activation volume of charge carriers are determined as 1.29 +/- 0.12 eV and 2.01 +/- 0.57 cm(3)/mol, respectively. The dominant electrical conduction mechanism of anhydrous almandine-rich garnet is the Fe2+ -> Fe3+ hopping of small polaron. At 3.0 GPa, electrical conductivity of almandine-rich garnet increases with increasing oxygen fugacity. The electrical conductivity of this sample can be represented by the relation Log(10)sigma = (2.67 +/- 0.05) + (0.054 +/- 0.003)(n) over tilde log(10)f(O2) + (-5446+/-68)/T, where f(O2) is the oxygen fugacity (bar) and T is the absolute temperature (K). At a typical temperature and pressure in the upper mantle, the influence of oxygen fugacity is substantial.