Effect of temperature, pressure and iron content on the electrical conductivity of olivine and its high-pressure polymorphs
Effect of temperature, pressure and iron content on the electrical conductivity of olivine and its high-pressure polymorphs
复制标题
温度、压力和铁含量对橄榄石及其高压多晶型物电导率的影响
DOI：
10.1029/2011jb008774
复制
发表时间：
2012
期刊：
影响因子：
--
通讯作者：
K.Funakoshi
中科院分区：
文献类型：
--
作者：
Yoshino;T.;A.Shimojuku;S.Shan;X.Guo;D.Yamazaki;E.Ito;Y.Higo;K.Funakoshi
在 Kawai 型多砧仪中，在覆盖橄榄石、硅锰矿和尖角橄榄石稳定场的各种压力 (P) 和温度 (T) 条件下测量了不同铁含量的橄榄石及其高压多晶型物 [XFe= Fe/(Fe + Mg) = 0.1、0.2、0.3、0.5、0.7 和 1.0] 的电导率。使用 MgO 的原位 X 射线衍射作为 SPring 8 中的压力标记来确定压力。使用钼电极，使氧逸度与铁方铁矿缓冲液的氧逸度相似。从低压相到高压相的转变导致电导率的增加。在各相的稳定场中，在恒定温度下，电导率随着压力的增加而略有增加，表明活化体积为负。电导率随着各相总铁含量的增加而增加。所有电导率数据均符合电导率公式σ=σ0XFeexp{−[ΔE0−αXFe1/3+ P(ΔV0−βXFe)]/kT}，其中σ0为指前项，ΔE0和ΔV0分别为极低总铁浓度下的活化能和活化体积，k为玻尔兹曼常数。随着橄榄石和尖橄榄石中总铁含量的增加，活化能降低。活化能对总 Fe 含量的依赖性表明电荷传输的主要机制是 Fe2+-Fe3+ 跳跃（小极化子）。橄榄石及其高压多晶型物中小极化子传导的活化体积往往随着总铁含量的增加而减小。对于Fe含量较低的橄榄石，小极化子传导的活化体积仍然为负且很小。假设Fe含量恒定（XFe=0.1）和氧气缓冲条件，电导率将随着深度的增加而增加，主要是由于沿地幔绝热温度的增加。
The electrical conductivity of olivine and its high‐pressure polymorphs with various iron contents [XFe= Fe/(Fe + Mg) = 0.1, 0.2, 0.3, 0.5, 0.7 and 1.0] was measured over a wide range of pressure (P) and temperature (T) conditions covering the stability field of olivine, wadsleyite and ringwoodite in a Kawai‐type multianvil apparatus. The pressure was determined using in situ X‐ray diffraction of MgO as a pressure marker in SPring 8. Molybdenum electrodes were used so that oxygen fugacity is similar to that for the iron‐wüstite buffer. The transition from low‐pressure phase to high‐pressure phase led to an increase of conductivity. In the stability field of each phase, the electrical conductivity slightly increased with increasing pressure at a constant temperature, suggesting a negative activation volume. The conductivity increased with increasing total iron content for each phase. All electrical conductivity data fit the formula for electrical conductivityσ=σ0XFeexp{−[ΔE0−αXFe1/3+ P(ΔV0−βXFe)]/kT}, whereσ0is the pre‐exponential term, ΔE0and ΔV0are the activation energy and the activation volume at very low total iron concentration, respectively, andkis the Boltzmann constant. The activation energy decreased with increasing total Fe content in olivine and ringwoodite. Dependence of the activation energy on the total Fe content suggests that the dominant mechanism of charge transport is Fe2+‐Fe3+hopping (small polaron). The activation volume for small polaron conduction in olivine and its high‐pressure polymorphs tends to decrease with total Fe content. For olivine with low Fe content, the activation volume for small polaron conduction still is negative and very small. Assuming constant Fe content (XFe= 0.1) and oxygen buffer condition, the conductivity will increase with depth mainly due to the increase of the temperature along the mantle adiabat.