拉曼光谱对含Cr镁铝尖晶石热处理及其有序-无序相变研究

尖晶石的有序-无序相变作为尖晶石的一种重要性质,在国内缺少相关研究成果。运用拉曼光谱仪通过785 nm激光在液氮环境下激发含Cr的宝石级天然粉红色尖晶石,避免了532 nm激光激发下产生的469 nm的荧光峰和在常温测试下由于热振动对光谱的影响,得到清晰尖锐的拉曼光谱,为拉曼光谱参数的分析奠定基础。同时通过对一颗Cr元素致色的天然粉色镁铝尖晶石进行热处理使尖晶石逐步发生有序-无序相变,并反映在拉曼光谱的谱峰参数之中。各项参数分析结果显示,尖晶石的拉曼光谱主要由E_g,T_2g(1),T_2g(2),N₃和A_g,五种振动模式产生,其谱峰位置分别为407.8,312.4,667.5,720.0和769.0 cm-1;尖晶石拉曼光谱谱峰参数在800 ℃时发生突变： 各谱峰半高宽和各峰相对主峰E_g峰的相对强度明显增大,常温下几乎不可见的N₃峰在高温处理后出现,并且T_2g(1)峰向低波数偏移,T_2g(2)向高波数偏移,同时峰的对称性逐渐消失。研究结果表明尖晶石的有序-无序相变可以通过拉曼光谱检测并且可以通过谱峰参数： 半高宽、谱峰相对高度等进行半定量表征。由于拉曼光谱具有的无损检测特点,使其成为宝石级热处理尖晶石鉴定应用的重要参考依据之一。

Raman Spectra Study of Heating Treatment and Order-Disorder Transition of Cr3+-Doped MgAl2O4 Spinel

Order-disorder transition is one of the important properties of spinel, but seldom research can be found about it. One nature Burma pink spinel were tested by Raman spectroscopy, excited by 785 nm laser in the liquid nitrogen atmosphere to obtain the clear and sharp Raman spectra. In this way, one can avoid the 469 nm fluorescence peak induced by the 532 nm laser, and the thermal affection of the room temperature test. One nature pink Cr-doped MgAl₂O₄ spinel were used in this study. The Raman spectra were obtained after the samples were heated at different temperatures to present the process of Raman spectra variation during spinel order-disorder transition. The parameter analysis showed the results that: the Raman peaks of MgAl₂O₄ spinel are caused by 5 vibrational mode, E_g,T_2g(1),T_2g(2),N₃ and A_g, at 407.8,312.4,667.5,720.0 and 769.0 cm-1; The parameter of Raman peaks have a sudden change at around 800 ℃, including the increase of HWFM of all the peaks and the relative intensities of the other peaks and the main peak E_g; the appearance of N₃ peak; and position movement of T_2g(1) (to the low wavenumber direction) and T_2g(2)(to the high wavenumber direction) peaks with the disappearance of peak symmetry. This study indicates that the peak parameters of Raman peaks can be used to show the order-disorder transition of spinel, and it can be widely used in the identification of heat treated spinel gems.