莫約在30億至40億年前，地球水含量比現今多了兩倍以上，目前認為早期地球的水可能被蘊藏在地函之中。來自上部地函的擄獲岩內常發現結構中含有水(羥基)的矽酸鹽礦物，是探究地球內部水含量與水循環的重要窗口。主要礦物包含橄欖石、輝石或石榴子石等，羥基以缺陷型式參雜其中，因此被稱為名義上無水礦物（nominally anhydrous minerals,簡稱NAMs）。地球深部的水，深刻影響著地球動力學行為。例如軟流圈的形成；礦物含水與脫水機制引發隱沒帶地震。此外，亦造成礦物物理性質改變。前人研究指出含水橄欖石含水量增加地震波波速下降；單晶含水頑火輝石含水量增加熱傳導率下降，且平行晶軸c軸方向較a軸方向顯著。羥基耦合機制對礦物物理性質改變及造成礦物非均向性，影響地球物理觀測。釐清名義上無水礦物（NAMs）羥基耦合機制，可幫助釐清含水對地球物理觀測影響。
名義上無水礦物羥基耦合機制利用光譜學搭配理論計算進行研究，然而由於上部地函礦物相(橄欖石、輝石或石榴子石等)化學成分與結構較為複雜，目前尚未為釐清光譜學中特徵峰指示羥基耦合於矽氧四面體或是陽離子多面體。因此本研究選定柯石英(Coesite)-單純[SiO4]2-架狀結構且在高壓下有水環境合成時有被觀察到[OH-]參入結構中，並藉由光譜學繼而釐清以上地函礦物相中[SiO4]2-與羥基耦合有關的特徵峰。
過去研究指出柯石英羥基耦合與特徵峰關係，然而研究以偏光顯微鏡做為定向依據，並結合常壓及高壓傅立葉轉換紅外線光譜與單晶X光繞射結釐清羥基耦合。本研究則以單晶X光繞射做為晶體定向依據，並比較d(O…O)變化去探討羫基在含水柯石英中可能位置。實驗結果指示:(1)由於晶體本身的光軸與晶軸夾角存在一定的誤差範圍，以單晶X光繞射技術可做為晶體絕對定向依據，以判定羥基方向。(2)柯石英羥基拉伸振動模ν1、ν2a、ν3、ν4 、ν5與O5-H1···O5(ν1)、O3-H2···O3(ν2a)、O4-H3···O5(ν3)、O3-H4···O4(ν4)、O3-H5 ···O5(ν5)羥基振動相關，未來將提供理論計算釐清與矽氧四面體相關的羥基耦合。
此外，值得注意的是本研究以Si-O-H起始原料合成含水柯石英，成功在4GPa環境中合成出含水量40ppm柯石英，降低其合成壓力。以該原料合成之含水柯石英，無在傅立葉轉換紅外線光譜觀察到新的羥基拉伸振動模，指示含水柯石英羥基耦合機制不受起始原料之不同鍵結環境影響。單晶X光繞射之柯石英晶體定向，除了協助本研究判定羥基方向，本研究亦利用偏振光拉曼散射光譜收取特定方向圖譜，作為快速判定方向的依據。

NAMs have profound effects on physical properties such as electrical/thermal conductivity and elastic modulus. For example, the thermal conductivity of single-crystal orthoenstatite at ambient is more significant in the direction of parallel c-axis than in the direction of a-axis, so we can understand the effect of non-homogeneous on physical properties of minerals. The mineral phases in upper mantle are all silicate minerals, which are composed of a silicon-oxygen tetrahedral structure([SiO4]2-) and cationic polyhedra in different arrangements, and the complex structure and composition make it difficult to determine the hydroxyl bonding environment. Therefore, this study aims to understand the bonding environment of pure SiO2 high-pressure phase, Coesite, and then to clarify the vibrational modes related to the hydroxyl groups coupled with pure silica-oxygen tetrahedra in the above geomorphic mineral phases.
In this study, SCXRD was used to provide precise crystal orientation. The OH position should be in O5-H1···O5(ν1)、O3-H2···O3(ν2a)、O4-H3···O5(ν3)、O3-H4···O4(ν4)、O3-H5···O5(ν5). Also, we suggest that 3520cm-1 belongs to ν2 rather than ν6c. Furthermore, we used Si-O-H starting material to synthesis hydrous coesite(40ppm) under 4GPa, reducing its synthesis pressure addition. Si-O-H starting material provides all the OH coupling mechanisms for hydrous coesite which indicates the OH coupling mechanism is not affected by different bonding environments in the starting material.

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