稀土羟基碳酸盐是自然界稀土元素最基本的碳酸盐矿物形式, RE(CO3)OH, 是稀土碳酸盐类矿物和含水稀土碳酸盐矿物中的主要组成部分, 在自然界有天然产出, 同时碳酸盐矿物又是地球深部碳循环最重要的载体矿物, 作为稀土元素主要的碳酸盐载体矿物, 六方羟基碳酸钐稳定的结构能为稀土元素迁移提供稳定载体。 目前对其结构中羟基氧配位连接方式及氢原子的准确占位情况的认识还存在许多争议, 羟基碳酸盐类矿物研究还处在初级阶段, 羟基对碳酸盐类矿物结构的影响的研究仍十分欠缺。 采用六面砧大压机在高温高压(3 GPa, 800 ℃)下合成, 粒度为10～20 μm六方羟基碳酸钐单晶集合体。 通过X射线单晶衍射分析得出, 羟基碳酸钐为六方晶系, a=b=12.214 3(7) , c=9.839 3(6) , V=1 271.26(17) 3, 属P 6空间群。 晶体结构模型显示在ab平面内, 由Sm3+和［OH］-连接形成六方网, 构成基本重复单层２∞［(ＯＨ)Ｓｍ３／３］２＋, 碳酸根基团连接各层沿c轴延伸, 中心Sm3+呈9配位形式, 与5个碳酸基团相连, 其中4个单齿连接一个螯合连接; 与3个羟基氧原子相连, 确定配位多面体的具体形式。 利用红外吸收光谱、 拉曼光谱两种分析方法对初始样品结构进一步表征, 尤其是对结构中的水进行了详细的解析。 通过样品光谱学特征分析其内部基团振动模式与结构类型, 特别是羟基在晶体结构中准确位置及振动特征。 研究表明: 六方羟基碳酸钐晶体中存在两种不同连接位态的羟基, 3 600～3 650 cm-1谱带对应极化方向垂直(001)晶面, 未能与层内氧原子形成氢键的羟基振动; 3 450～3 500 cm-1谱带对应极化方向平行(001)晶面, 可与层内氧原子形成氢键的羟基振动; 3 369～3 380 cm-1谱带反应层间羟基的振动, 更低频段3 230～3 250 cm-1谱带则是O—H键长更短的羟基振动的体现。 利用氘代样的红外吸收光谱验证H-D置换实验, 由于D原子取代了H原子, 导致ρOH摆动振动和νOH伸缩振动吸收峰消失, 在2608.12cm-1处出现O-D振动吸收峰, 标志氘代完全, 验证了氘代实验设计可行。 作为可以改变岩浆地球动力学性质的羟基, 常温常压下属性及矿物物理性质等对地球科学的基础研究有重要的参考价值。

Rare earth hydroxyl carbonate is an essential carbonate mineral form for rare earth elements in nature, and RE(CO3)OH is the main component of rare earth carbonate minerals and aqueous rare earth carbonate minerals. The mineral is present in nature. At the same time, carbonate minerals are the most important carrier minerals in the deep carbon cycle of the earth. As the main carbonate carrier minerals of rare earth elements, the stable structure of hexagonal RE(CO3)OH can provide a stable carrier for the migration of rare earth elements. At present, there are still many controversies on the way of the hydroxyl oxygen coordination and the exact occupation of hydrogen atoms, and the study of hydroxyl carbonate minerals is still in the primary stage. The effect of hydroxyl groups on the structure of carbonate minerals is still lacking. In this experiment, the hexagonal Sm(CO3)OH single crystal was synthesized by DS6×600t cubic-anvil-apparatus under the condition of 3 GPa and 800 ℃ with a particle size of 10～20 μm. The results of X-ray single crystal diffraction show that Sm(CO3)OH is hexagonal, with a=b=12.214 3(7) , c=9.839 3(6) , V=1 271.26(17) 3, and belongs to P6 space group. The structure shows that in the ab plane, the hexagonal network is formed by Sm3+ and ［OH］- connection, forming a basic repeating monolayer ２∞［(ＯＨ)Ｓｍ３／３］２＋. And ［CO3］2- connected these layers along c-axis, and the central Sm3+ is in the form of 9 coordination, connected with five carbonates,four monodentates are linked to a chelating junction, and the specific form of the coordination polyhedron is determined by connecting with three hydroxyl oxygen atoms. In this paper, the structure of the initial sample was further characterized by Infrared and Raman spectroscopy, especially OH- in the structure was analyzed in detail. The vibration modes and structure types of the inner groups were analyzed by the spectroscopic characteristics of the samples, especially the exact position and vibration characteristics of hydroxyl groups in the crystal structure. Infrared and Raman spectroscopy study indicated there were two different types of OH- in the structure of hexagonal Sm(CO3)OH. In both TF-IR and Raman spectra, band of 3 600~3 650 cm-1 was attributed to the hydroxyl groups polarized perpendicular to the (001) plane without hydrogen bonds and band of 3 450~3 500 cm-1 to the hydroxyl groups polarized in the (001) plane with hydrogen bonds,and the hydroxyl vibration of the reaction layer in the 3 369~3 380 cm-1 band and the 3 230~3 250 cm-1 band in the lower frequency band is the embodiment of the hydroxyl vibration with shorter O—H bond length. The H-D replacement experiment was verified by infrared absorption spectrum of deuterium sample. Because D atom replaced H atom, ρOH oscillating vibration and νOH stretching vibration absorption peak disappeared, O-D vibrational absorption peak appeared at 2 608.12 cm-1, indicating that deuterium generation was complete. The feasibility of deuterium generation experimental design was verified. As the hydroxyl groups which can change the characteristics of magmatic geodynamics, the properties at room temperature and atmospheric pressure and the physical properties of minerals provide important basic research value for geoscience problems.