Hydrogen site analysis of hydrous ringwoodite in mantle transition zone by pulsed neutron diffraction
Hydrogen site analysis of hydrous ringwoodite in mantle transition zone by pulsed neutron diffraction
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DOI：
10.1002/2014gl061448
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发表时间：
2014-10
影响因子：
5.2
通讯作者：
N. Purevjav;T. Okuchi;N. Tomioka;J. Abe;S. Harjo
中科院分区：
文献类型：
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作者：
N. Purevjav;T. Okuchi;N. Tomioka;J. Abe;S. Harjo
在日本质子加速器研究综合体（J-PARC）的脉冲中子源上进行的高分辨率中子粉末衍射首次确定了合成含水灵伍德石晶体结构中的氢位置和占位。它表明，氢交换不仅与镁或铁，但也与硅阳离子形成羟基和氢键，无论是在相关的八面体或四面体由周围的氧阴离子。水合八面体收缩，而水合四面体膨胀。八面体和四面体的同时水合作用的发生因此被明确地证实，其中后者在降低地震速度和提高高压和高温下的林伍德石的导电性方面起着特别独特的作用。这些结果对探讨地幔过渡带中含水林伍德岩的物理性质和估算地幔过渡带的实际含水量具有重要意义。
Hydrogen site positions and occupancies in the crystal structure of synthetic hydrous ringwoodite have been determined for the first time by high‐resolution neutron powder diffraction conducted at the pulsed neutron source at Japan Proton Accelerator Research Complex (J‐PARC). It is demonstrated that hydrogen exchanges not only with Mg or Fe but also with Si cations to form hydroxyl and hydrogen bonding, both within the relevant octahedra or tetrahedra created by their surrounding oxygen anions. The hydrated octahedra shrink, whereas the hydrated tetrahedra expand. The occurrence of simultaneous hydration of octahedra and tetraheda is thus unambiguously confirmed, whereby the latter plays an especially unique role in reducing seismic velocity and for enhancing the electrical conductivity of ringwoodite at high pressures and temperatures. These results provide distinctive implications for discussing the physical properties of hydrous ringwoodite occurring in the mantle transition zone and evaluating the actual water content in the zone.