1.0～4.4GPa下奥长石拉曼光谱特征的变化

常温、1.0～4.4GPa下,利用激光拉曼光谱研究了奥长石晶体结构随压力的变化。发现,压力为2.9GPa时,517cm-1附近出现新的谱峰,奥长石开始相变。3.4GPa时,源于奥长石结构中M—O伸缩振动的288cm-1拉曼谱峰频移发生突变,517cm-1附近谱峰消失,奥长石由三斜晶系完全相变为单斜晶系(P1-I1)。随压力增加,归属于奥长石四面体结构中Si—O—Si弯曲振动的458及516cm-1谱峰随压力增加有规律地向高频方向偏移,斜率分别是1.667cm-1/GPa和3.560cm-1/GPa,而源于Al—O—Al弯曲振动的480cm-1谱峰与压力没有明显的线性变化关系。卸压过程中,288cm-1拉曼谱峰频移保持不变,458,480及516cm-1谱峰向低频偏移。长石类矿物的相变压力与结构中八元环所含阳离子种类有关。

Variation of Raman spectra of oligoclase under 1.0-4.4 GPa

Variation of crystal structure of oligoclase with pressure was investigated by the approach of diamond anvil cell (DAC) and in situ micro-Raman spectroscopic measurement at room temperature and under pressures from 1.0 to 4.4 GPa. At 2.9 GPa a new peak round 517 cm(-1) appeared, and a new phase was produced. Near 3.4 GPa a major discontinuity occurs in the pressure dependence of 288 cm(-1) peak arising from the stretching mode of M-O, and 517 cm(-1) peak disappeared, it implied that the oligoclase underwent triclinic to monoclinic phase transition completely at about 3.4 GPa. The peaks at 458 and 516 cm(-1) peaks arising from flexural vibrational mode of Si-O-Si shifted linearly with the increasing pressures, the pressure-related slopes are 1.667 cm(-1)/GPa and 3.560 cm(-1)/GPa, respectively, whereas, the flexural vibrational mode of Al-O-Al at 480 cm(-1) did not shifted linearly with the increasing pressures. The position of 288 cm(-1) peak did not change obviously in comparision with 458, 516 and 480 cm(-1) peaks, which shifted to lower frequency during decompression. The phase transition pressure of feldspar relates to the species of cation in the octatomic rings.