中国科学院地球化学研究所机构知识库

Under conditions of 1.0 ~ 3.0 GPa, 973 ~ 1273 K and frequency range from 10^- 2 to 10⁶ Hz, the electrical conductivity of Fe-rich garnet single crystal is measured by virtue of YJ-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 (10²-10⁶ Hz) showing a semicircular arc originated from the origin in the Nyquist and Bode diagram, another small tail in the low frequency of 10^- 2-10² Hz. Experimental results show that with the rise of temperature (T), electrical conductivity (σ) tends to increase, and Log σ 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 cm³/mol, respectively. The dominant electrical conduction mechanism of anhydrous almandine-rich garnet is the Fe^2 + → Fe^3 + 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 Log10σ=2.67±0.05+0.054±0.003×log10fO2+−5446±68T, where fO2 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.