Li_2B_4O_7晶体及其熔体结构的拉曼光谱研究

Raman Spectroscopic Study of Li_2B_4O_7 Crystal and Melt Structure

采用高温原位拉曼光谱技术,研究了Li_2B_4O_7从常温至1 373K温度范围内的拉曼光谱。在升温过程中,晶体的拉曼光谱出现展宽和红移现象,且强度降低。晶体熔化时,由2个[BO_4]和2个[BO_3]组成的[B_4O_9]环状结构转变成(B_3O_6)^(3-)六元环和[BO_3]结构,[BO_4]结构减少直至消失。基于密度泛函理论,计算了Li_2B_4O_7晶体的拉曼光谱,对其振动模式进行了分析归属。利用量子化学从头计算法计算了由[B_3O_6-BO_3]为基础相互连接形成的x(Li_2B_4O_7)(x=2,3,…,9)的环状团簇模型的拉曼光谱,对Li_2B_4O_7熔体的结构进行了模拟分析。计算结果表明Li_2B_4O_7熔体的阴离子基元为三个(B_3O_6-BO_3)组成的大三元环超级结构。

Raman spectra of Li2B4O7at different temperatures up to 1 373K were recorded by using in situ high temperature Raman spectroscopic technique.With the increase of temperature,Raman spectra of crystal broaden and decrease in wavenumber and intensity.During the melting process,[B4O9]rings which consist of two[BO4]and two[BO3]turned into（B3O6）^（3-）sixmembered ring and[BO3],[BO4]species decreased and then disappeared.In addition,the vibrational modes of the Li2B4O7crystal were simulated and assigned by using density functional theory（DFT）method.Raman spectra of x（Li2B4O7）（x=2,3,…,9）rings which consist of（B3O6-BO3）were calculated by using quantum chemistry ab initio method,to analyze the cluster in melt.It can be concluded that there exists super ring structure which contains three（B3O6-BO3）rings connected with each other.