The pressure-induced local structural change around tungsten in silicate glass
The pressure-induced local structural change around tungsten in silicate glass
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DOI：
10.7185/geochemlet.2116
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发表时间：
2021-06-01
影响因子：
4.9
通讯作者：
Takahashi, Y.
中科院分区：
文献类型：
--
作者：
Ozawa, K.;Hirose, K.;Takahashi, Y.
钨是了解行星内核形成条件和时间的关键元素之一。虽然钨的金属-硅酸盐配分已被广泛研究，但压力和硅酸盐熔体成分的影响一直存在争议。本文利用EXAFS光谱研究了高达67 GPa的玄武岩玻璃中钨的局部环境，发现W-O键长在10 ~ 32 GPa的压力范围内增加，表明W6+离子使配位数从4增加到6。已知在相似的压力范围内，硅的配位也会发生变化，提示微量元素钨的配位结构可能受Si-O配位控制。钨的配位变化会影响其金属硅酸盐分配，并可能解释之前观察到的压力效应在5 GPa左右的变化，当考虑熔体与玻璃的差异时。这也表明，在32 GPa以上，钨主要是六倍配位的压力依赖性进一步变化。此外，在此压力范围内，硅酸盐熔体成分的影响可能会减弱。
Tungsten is one of the key elements to understand the conditions and timing of planetary core formation. While the metal-silicate partitioning of tungsten has been extensively studied, the effects of pressure and silicate melt composition have been controversial. Here we have investigated the local environment of tungsten in a basaltic glass up to 67 GPa based on EXAFS spectroscopy and found that the W-O bond length increases in a pressure range from 10 to 32 GPa, indicating that W6+ ion increases the coordination number from four to six. It is known that the coordination of silicon also changes at similar pressure range, suggesting that the coordination structure of trace element tungsten may be controlled by the Si-O coordination. The coordination change of tungsten will affect its metal-silicate partitioning and may explain the previously observed change in the pressure effect around 5 GPa, when considering the difference between melt and glass. This also suggests further change in the pressure dependence above 32 GPa where tungsten is predominantly sixfold coordinated. In addition, the effect of silicate melt composition may diminish at such pressure range.