TY - JOUR
T1 - Negative activation volume of oxygen self-diffusion in forsterite
AU - Fei, Hongzhan
AU - Wiedenbeck, Michael
AU - Sakamoto, Naoya
AU - Yurimoto, Hisayoshi
AU - Yoshino, Takashi
AU - Yamazaki, Daisuke
AU - Katsura, Tomoo
N1 - Funding Information:
We thank S. Chakraborty and R. Dohmen at Ruhr-University of Bochum for their help in thin film deposition, A. Yoneda at Okayama University for purchasing the high quality single crystal, A. Audétat for ICP-MS analysis, T. Boffa-Ballaran for X-ray diffraction analysis, K. Marquardt for TEM observation, and C. Zhao for valuable discussions. This work was funded by the Deutsche Forschungsgesellschaft (KA3434/3-1, KA3434/7-1, KA3434/8-1 and KA3434/9-1) to T. Katsura, the JSPS program ( Japan Society for the Promotion of Science ) to H. Fei ( 25003327 ), and the ENB (Elite Network Bavaria) program.
Publisher Copyright:
© 2017 Elsevier B.V.
Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 2018/2
Y1 - 2018/2
N2 - Oxygen self-diffusion coefficients (DOx) were measured in single crystals of dry synthetic iron-free olivine (forsterite, Mg2SiO4) at a temperature of 1600 K and under pressures in the range 10−4 to 13 GPa, using a Kawai-type multi-anvil apparatus and an ambient pressure furnace. Diffusion profiles were obtained by secondary ion mass spectrometry operating in depth profiling mode. DOx in forsterite increases with increasing pressure with an activation volume of −3.9 ± 1.2 cm3/mol. Although Mg is the fastest diffusing species in forsterite under low-pressure conditions, O is the fastest diffusing species at pressures greater than ∼10 GPa. Si is the slowest throughout the stable pressure range of forsterite. Based on the observed positive and negative pressure dependence of DOx and DMg (Mg self-diffusion coefficient), respectively, DOx + DMg in forsterite decreases with increasing pressure, and then increases slightly at pressures greater than 10 GPa. This behavior is in agreement with the pressure dependence of ionic conductivity in forsterite based on conductivity measurements (Yoshino et al., 2017), and can be used to explain the conductivity increase from ∼300 km depth to the bottom of the asthenosphere.
AB - Oxygen self-diffusion coefficients (DOx) were measured in single crystals of dry synthetic iron-free olivine (forsterite, Mg2SiO4) at a temperature of 1600 K and under pressures in the range 10−4 to 13 GPa, using a Kawai-type multi-anvil apparatus and an ambient pressure furnace. Diffusion profiles were obtained by secondary ion mass spectrometry operating in depth profiling mode. DOx in forsterite increases with increasing pressure with an activation volume of −3.9 ± 1.2 cm3/mol. Although Mg is the fastest diffusing species in forsterite under low-pressure conditions, O is the fastest diffusing species at pressures greater than ∼10 GPa. Si is the slowest throughout the stable pressure range of forsterite. Based on the observed positive and negative pressure dependence of DOx and DMg (Mg self-diffusion coefficient), respectively, DOx + DMg in forsterite decreases with increasing pressure, and then increases slightly at pressures greater than 10 GPa. This behavior is in agreement with the pressure dependence of ionic conductivity in forsterite based on conductivity measurements (Yoshino et al., 2017), and can be used to explain the conductivity increase from ∼300 km depth to the bottom of the asthenosphere.
KW - Activation volume
KW - Forsterite
KW - Ionic conductivity
KW - Oxygen self-diffusion
KW - Pressure dependence
KW - Upper mantle
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U2 - 10.1016/j.pepi.2017.12.005
DO - 10.1016/j.pepi.2017.12.005
M3 - Article
AN - SCOPUS:85038887390
SN - 0031-9201
VL - 275
SP - 1
EP - 8
JO - Physics of the Earth and Planetary Interiors
JF - Physics of the Earth and Planetary Interiors
ER -