Location and quantification of hydroxyl in wadsleyite: New insights
Location and quantification of hydroxyl in wadsleyite: New insights
复制标题
瓦兹利石中羟基的定位和定量：新见解
DOI：
10.2138/am.2010.3267
复制
发表时间：
2010
影响因子：
3.1
通讯作者：
S. Thomas
中科院分区：
文献类型：
--
作者：
F. Deon;M. Koch‐Müller;D. Rhede;M. Gottschalk;R. Wirth;S. Thomas
摘要 在多砧压机中，在 13.3-13.5 GPa、1150-1200 °C 下合成了无水和水合硅锰矿，并通过傅里叶变换红外 (FTIR) 光谱、单晶 X 射线细化 (SC-XRD) 和电子微探针分析 (EMPA) 进行了研究。 FTIR 光谱与之前的数据一致，即光谱以 3380 cm-1 附近的宽带为主，除了 3600 cm-1 附近一些较弱的 OH 谱带外，还可以解析为 3326 (ν2)、3382 (ν3) 和 3546 (ν4) cm-1 三个谱带。我们确认瓦兹利石含有 wt% 范围内的水，并且当使用二次离子质谱 (SIMS) 和拉曼光谱时，浓度随着温度的降低而急剧增加。定量与 FTIR 光谱相结合，使我们开发出第一个瓦兹利石中水的红外校准，即计算 εi,tot 为 73 000 ± 7000 (L mol-1H2O cm-2)。对含有 8000 ± 1000 wt ppm H2O 的水合瓦兹利石 FD0718 进行 SC-XRD 测定，证明 M3 位点处存在 Mg 空位，如前所述。此外，我们发现电子密度图中的最大值靠近假设无水结构的 M3 八面体的 O 原子 O1 和 O3。根据我们的新数据，我们认为瓦兹利石中的主要质子化发生在空的 M3 八面体的 O1·O4 (3.1 Å) 和 O3·O4 (3.05 Å) 边缘。 H-掺入似乎是随机的，导致空的 M3 八面体的两个 O1、两个 O3 或一个 O1 和一个 O3 质子化。通过此作业，现在可以解释观察到的环境和高压红外图案。
Abstract Anhydrous and hydrous wadsleyite were synthesized at 13.3-13.5 GPa and 1150-1200 °C in a multianvil press and investigated by Fourier transform infrared (FTIR) spectroscopy, single-crystal X-ray refinement (SC-XRD), and electron microprobe analyses (EMPA). The FTIR spectra agree with previous data, i.e., the spectra are dominated by a broad band around 3380 cm-1, resolvable in three bands 3326 (ν2), 3382 (ν3), and 3546 (ν4) cm-1 besides some weaker OH-bands around 3600 cm-1. We confirm that wadsleyite incorporates water in the wt% range and that the concentration strongly increases with decreasing temperature when using secondary ion mass spectrometry (SIMS) and Raman spectroscopy. The quantifications combined with FTIR spectra led us to develop the first IR calibration for water in wadsleyite, i.e., calculating an εi,tot of 73 000 ± 7000 (L mol-1H₂O cm-2). A SC-XRD determination of hydrous wadsleyite FD0718, bearing 8000 ± 1000 wt ppm H2O, certifies the presence of Mg vacancies at the M3 sites as previously suggested. Furthermore, we found maxima in the electron density map close to the O atoms O1 and O3 of an M3 octahedron assuming the anhydrous structure. Based on our new data we suggest that the main protonation in wadsleyite occurs along the O1···O4 (3.1 Å) and O3···O4 (3.05 Å) edges of a vacant M3 octahedron. H-incorporation seems to be random leading to protonation of either two O1, two O3, or one O1 and one O3 of the vacant M3 octahedra. With this assignment, the observed ambient and high-pressure IR pattern can now be explained.