TY - JOUR
T1 - Effect of temperature, pressure and iron content on the electrical conductivity of orthopyroxene
AU - Zhang, Baohua
AU - Yoshino, Takashi
N1 - Funding Information:
Two anonymous reviewers provided constructive comments and reviews that improved this paper. We would like to thank Fang Xu for XRD analysis, Shigeru Yamashita and Chengcheng Zhao for FT-IR measurements, and Daisuke Yamazaki, Akira Yoneda, Eiji Ito for their suggestions and discussions. This study was supported by the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (XDB 18010401), the 1000Plan Program for Young Talents, Hundred Talent Program of CAS and NSF of China (41303048) to BZ, and also partially supported by the International Cooperative Research Program of Institute for Planetary Materials, Okayama University.
Publisher Copyright:
© 2016, Springer-Verlag Berlin Heidelberg.
PY - 2016/12/1
Y1 - 2016/12/1
N2 - 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.
AB - 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.
KW - Electrical conductivity
KW - Iron content
KW - Orthopyroxene
KW - Small polaron
KW - Upper mantle
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U2 - 10.1007/s00410-016-1315-z
DO - 10.1007/s00410-016-1315-z
M3 - Article
AN - SCOPUS:84995812361
SN - 0010-7999
VL - 171
JO - Contributions of Mineralogy and Petrology
JF - Contributions of Mineralogy and Petrology
IS - 12
M1 - 102
ER -