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Pressure dependence of electrical conductivity in forsterite
Author(s) -
Yoshino Takashi,
Zhang Baohua,
Rhymer Brandon,
Zhao Chengcheng,
Fei Hongzhan
Publication year - 2017
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1002/2016jb013555
Subject(s) - forsterite , ionic conductivity , thermal conduction , polaron , materials science , olivine , conductivity , electrical resistivity and conductivity , activation energy , mineralogy , vacancy defect , analytical chemistry (journal) , chemistry , crystallography , composite material , electrode , electrolyte , electron , physics , quantum mechanics , chromatography , electrical engineering , engineering
Electrical conductivity of dry forsterite has been measured in muli‐anvil apparatus to investigate the pressure dependence of ionic conduction in forsterite. The starting materials for the conductivity experiments were a synthetic forsterite single crystal and a sintered forsterite aggregate synthesized from oxide mixture. Electrical conductivities were measured at 3.5, 6.7, 9.6, 12.1, and 14.9 GPa between 1300 and 2100 K. In the measured temperature range, the conductivity of single crystal forsterite decreases in the order of [001], [010], and [100]. In all cases, the conductivity decreases with increasing pressure and then becomes nearly constant for [100] and [001] and slightly increases above 7 GPa for [010] orientations and a polycrystalline forsterite sample. Pressure dependence of forsterite conductivity was considered as a change of the dominant conduction mechanism composed of migration of both magnesium and oxygen vacancies in forsterite. The activation energy (Δ E ) and activation volume (Δ V ) for ionic conduction due to migration of Mg vacancy were 1.8–2.7 eV and 5–19 cm 3 /mol, respectively, and for that due to O vacancy were 2.2–3.1 eV and −1.1 to 0.3 cm 3 /mol, respectively. The olivine conductivity model combined with small polaron conduction suggests that the most part of the upper mantle is controlled by ionic conduction rather than small polaron conduction. The previously observed negative pressure dependence of the conductivity of olivine with low iron content (Fo 90 ) can be explained by ionic conduction due to migration of Mg vacancies, which has a large positive activation volume.