Transport properties of olivine grain boundaries from electrical conductivity experiments
Transport properties of olivine grain boundaries from electrical conductivity experiments
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DOI：
10.1007/s00410-018-1468-z
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发表时间：
2018-04
影响因子：
3.5
通讯作者：
A. Pommier;D. Kohlstedt;L. Hansen;S. Mackwell;M. Tasaka;F. Heidelbach;K. Leinenweber
中科院分区：
文献类型：
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作者：
A. Pommier;D. Kohlstedt;L. Hansen;S. Mackwell;M. Tasaka;F. Heidelbach;K. Leinenweber
晶界过程对地球内部物质的电子和离子输运有重要贡献。我们报告了一个新的实验研究晶界电导率在高应变橄榄石聚集体，证明了相邻晶粒之间的取向差角聚集体的传输性能的重要性。我们对先前在1200 °C和0.3 GPa下变形至高达γ= 7.3的剪切应变的无熔体多晶橄榄石（Fo 90）样品进行了电导率测量。在700-1400 °C的温度范围内，在2.8 GPa下测量电导率和各向异性。我们观察到：（1）具有小晶粒尺寸（3-6 μm）和在大应变剪切变形期间由动态再结晶产生的强晶体学择优取向的样品的电导率是粗晶粒样品测量的电导率的10倍或更多，（2）变形到最高应变的样品是最导电的，即使它没有最小的晶粒尺寸，以及（3）在剪切方向上的电导率比垂直于剪切平面的电导率大~ 4倍。基于这些结果结合粗晶粒，多晶橄榄石和单晶的电导率数据，我们建议，我们的细晶粒样品的电导率是由晶界路径为主。此外，电各向异性的结果从优先排列的高电导率的晶界与发展的一个强大的晶体择优取向的晶粒。
Grain boundary processes contribute significantly to electronic and ionic transports in materials within Earth’s interior. We report a novel experimental study of grain boundary conductivity in highly strained olivine aggregates that demonstrates the importance of misorientation angle between adjacent grains on aggregate transport properties. We performed electrical conductivity measurements of melt-free polycrystalline olivine (Fo90) samples that had been previously deformed at 1200 °C and 0.3 GPa to shear strains up toγ= 7.3. The electrical conductivity and anisotropy were measured at 2.8 GPa over the temperature range 700–1400 °C. We observed that (1) the electrical conductivity of samples with a small grain size (3–6 µm) and strong crystallographic preferred orientation produced by dynamic recrystallization during large-strain shear deformation is a factor of 10 or more larger than that measured on coarse-grained samples, (2) the sample deformed to the highest strain is the most conductive even though it does not have the smallest grain size, and (3) conductivity is up to a factor of ~ 4 larger in the direction of shear than normal to the shear plane. Based on these results combined with electrical conductivity data for coarse-grained, polycrystalline olivine and for single crystals, we propose that the electrical conductivity of our fine-grained samples is dominated by grain boundary paths. In addition, the electrical anisotropy results from preferential alignment of higher-conductivity grain boundaries associated with the development of a strong crystallographic preferred orientation of the grains.