Pressure dependence of electrical conductivity in forsterite
Pressure dependence of electrical conductivity in forsterite
复制标题
DOI：
10.1002/2016jb013555
复制
发表时间：
2017-01
期刊：
影响因子：
--
通讯作者：
T. Yoshino;Baohua Zhang;B. Rhymer;Chengcheng Zhao;H. Fei
中科院分区：
文献类型：
--
作者：
T. Yoshino;Baohua Zhang;B. Rhymer;Chengcheng Zhao;H. Fei
用多砧仪测量了干燥的森林石的电导率，以研究森林石中离子电导率的压力依赖性。电导率实验的起始材料是合成的forsterite单晶和由氧化物混合物合成的烧结forsterite骨料。在1300和2100 K之间测量了3.5、6.7、9.6、12.1和14.9 GPa的电导率。在测量温度范围内，单晶forsterite的电导率按[001]、[010]、[100]的顺序递减。在所有情况下，电导率都随着压力的增加而下降，然后在[100]和[001]中趋于恒定，在[010]取向和多晶forsterite样品中电导率略高于7 GPa。研究认为，压力依赖性是由镁空位和氧空位迁移组成的主要传导机制的变化。Mg空位迁移离子传导的活化能（ΔE）和激活体积（ΔV）分别为1.8 ~ 2.7 eV和5 ~ 19 cm3/mol， O空位迁移离子传导的活化能（2.2 ~ 3.1 eV）和- 1.1 ~ 0.3 cm3/mol。橄榄石电导率模型结合小极化子电导率表明，上地幔大部分由离子电导率控制，而不是由小极化子电导率控制。先前观察到的低铁含量（Fo90）橄榄石电导率的负压依赖性可以用镁空位迁移引起的离子传导来解释，镁空位具有较大的正活化体积。
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 (ΔE) and activation volume (ΔV) for ionic conduction due to migration of Mg vacancy were 1.8–2.7 eV and 5–19 cm3/mol, respectively, and for that due to O vacancy were 2.2–3.1 eV and −1.1 to 0.3 cm3/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 (Fo90) can be explained by ionic conduction due to migration of Mg vacancies, which has a large positive activation volume.