白硅钙石的高温高压拉曼光谱研究

利用活塞圆筒装置在1.2 GPa，1 473 K的条件下合成了白硅钙石。采用外加热装置和金刚石压腔结合拉曼光谱分析技术，采集了白硅钙石298，353，463，543，663，773以及873 K温度区间的常压及1 atm～14.36 GPa(常温)压力区间的拉曼谱图。扫描电镜下，该研究合成的样品为结构一致的单一相，颗粒大小为10～20 μm。电子探针分析结果表明，样品的组成为Ca_7.03(2)Mg_0.98(2)Si_3.94(2)O₁₆，该组分完全吻合白硅钙石理论组分。Raman分析结果表明，高温时白硅钙石的拉曼谱图中具有29个振动峰。随着温度的升高，部分振动峰出现了合并或者弱化消失的现象。该现象尤其以800～1 200 cm-1范围内的909，927和950 cm-1振动峰峰位最为明显，这些振动峰分别在873，773以及873 K时弱化消失。据此，白硅钙石的结构在实验温压范围内稳定，且随着温度和压力的升高，其拉曼振动峰峰位分别呈现往低频和高频方向线性飘移的趋势。除此之外，根据高温和高压拉曼实验的结果，分别计算了白硅钙石拉曼振动峰峰位的等压mode-Grüneisen参数和等温mode-Grüneisen参数，其算术平均值分别为1.47(2)和0.45(3)。最后结合高温和高压拉曼实验的结果，计算了白硅钙石的非谐系数，结果表明，Si-O振动模式对于非谐效应的贡献要小于其他振动模式。

Raman Spectra of Bredigite at High Temperature and High Pressure

Bredigite was synthesized by using the Piston-Cylinder in 1.2 GPa and 1 473 K.With external heat-ing device and diamond anvil cell,high temperature and high pressure Raman spectra of bredigite were collect-ed at temperatures 298,353,463,543,663,773 and 873 K and with pressure from 1 atm up to 14.36 GPa (room temperature).The SEM image showed that the sample consisted of one crystalline phase with grain size ranging from 10~20μm.The EPMA data suggest a chemical formula of Ca7.03(2)Mg0.98(2)Si3.94(2)O16 which was identical to the theoretical component of bredigite.The Raman spectroscopic results indicate there were 29 vi-bration bands of bredigite at high temperature.Some bands were merging,weakening and disappearing in-creasingly with the temperature,which was obvious in the range of 800~1 200 cm-1 .The vibration bands of 909,927 and 950 cm-1 disappeared at 873,773 and 873 K,respectively.The results primarily indicated that the structure of bredigite was stable under experimental condition.In addition,isobaric mode-Grüneisen pa-rameters and isothermal mode-Grüneisen parameters were calculated,yielding 1.47(2)and 0.45(3)as their mean values,respectively.Anharmonic coefficients were estimated based on the high temperature and high pressure Raman experiments,showing that the contributions to anharmonic-effect induced with the Si—O vi-bration modes were smaller than other modes.