Effect of temperature, pressure and iron content on the electrical conductivity of orthopyroxene

Baohua Zhang, Takashi Yoshino

    Research output: Contribution to journalArticlepeer-review

    10 Citations (Scopus)

    Abstract

    The electrical conductivity of (Mg1−x, Fex)SiO3 orthopyroxene with various iron contents [XFe = Fe/(Fe + Mg) = 0, 0.1, 0.3, 0.5, 0.7 and 1.0] was measured in a Kawai-type multianvil apparatus by impedance spectroscopy over a wide range of pressure (P) and temperature (T) covering the stability field of orthopyroxene. Impedance spectroscopy measurements indicated that the electrical conductivity of orthopyroxene systematically increased with increasing total iron content. The conductivity slightly decreased with increasing pressure at a constant temperature. For samples with lower Fe content, two conduction mechanisms were identified from the Arrhenius behavior. A change in the activation enthalpy indicated that the dominant conduction mechanism changed from small polaron to ionic conduction with increasing temperature. At temperature below 1373 K, relatively low activation enthalpies and small positive activation volumes suggest that the dominant mechanism of charge transport is Fe2+‒Fe3+ hopping (small polaron). At higher temperatures above 1473 K, ionic conduction (via Mg vacancy mobility) dominates, with higher activation enthalpy exceeding 2 eV and larger positive activation volume. All electrical conductivity data fit the formula for electrical conductivity 03C3; = σ0 iexp [-(ΔE0i + p Δ + p σvoi/ kBT] is the pre-exponential term, ΔE0 and ΔV0 are the activation energy and the activation volume at very low total iron concentration, kB is the Boltzmann constant, T is the absolute temperature, and superscripts i and p denote the ionic and small polaron conductions, respectively. Electrical conductivity of Al-free orthopyroxene with XFe = 0.1 is distinctly lower than that of olivine with XFe = 0.1. Above 3 GPa Al content in orthopyroxene becomes smaller in association with garnet formation. Unless iron content in orthopyroxene is considerably high (XFe > 0.2), orthopyroxene has little influence on the electrical structure of the upper mantle.

    Original languageEnglish
    Article number102
    JournalContributions to Mineralogy and Petrology
    Volume171
    Issue number12
    DOIs
    Publication statusPublished - Dec 1 2016

    Keywords

    • Electrical conductivity
    • Iron content
    • Orthopyroxene
    • Small polaron
    • Upper mantle

    ASJC Scopus subject areas

    • Geophysics
    • Geochemistry and Petrology

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