碱金属阳离子对[B3O7]型非线性光学晶体结晶习性的影响

本文利用高温拉曼光谱技术和从头计算的方法, 研究了LiB₃O₅和CsB₃O₅晶体高温熔融体的结构, 分析了碱金属阳离子对熔体结构的影响, 以及熔体结构的差异与LiB₃O₅和CsB₃O₅晶体结晶习性的联系. 结果表明: LiB₃O₅和CsB₃O₅晶体高温熔融体中的结构基团 主要为B₃Ø₇和B₃Ø₆两种不同类型的硼氧六元环; 环内BØ₄ 四面体的数量影响了六元环呼吸振动峰的拉曼频率, 随BØ₄四面体数量的增加六元环呼吸振动峰向低频移动; LiB₃O₅晶体高温熔融体中, BØ₄四面体含量相对较多; 然而, 离子半径相对较大的Cs⁺离子却阻碍了熔体中BØ₄四面体的形成, 造成CsB₃O₅晶体高温熔融体中BØ₄/BØ₃比值的降低. 结合LiB₃O₅和CsB₃O₅晶体生长动力学过程的分析 (Wang D, Wan S M et al. 2011 Cryst. Eng. Comm. 13 5239), 阳离子的不同导致高温熔体中BØ₄四面体数量的差异, 被认为是影响LiB₃O₅和CsB₃O₅晶体结晶习性的重要因素, 有效降低高温熔体中BØ₄四面体的数量, 将是实现LiB₃O₅晶体生长的关键条件. 关键词： 硼酸盐晶体 熔体结构 拉曼光谱 结晶习性

The influence of alkali metal ions on crystallization habits of nonlinear optical crystal containing [B3O7] groups

LiB₃O₅ and CsB₃O₅ are two excellent nonlinear optical borate crystals containing B₃O₇] groups. With a difference of aikali metal ions in structure, LiB₃O₅ and CsB₃O₅ exhibit different crystallization habits. The former is an incongruent compound, which cannot crystallize from its melt; however, the latter is a congruent compound obtained by cooling its melt directly. In this work, using Raman spectroscopy and ab initio calculation, the structures of LiB₃O₅ and CsB₃O₅ melts have been investigated, and then the influence of alkali metal ions on melt structures is discussed, finally, the relationship between crystallization habits of LiB₃O₅ and CsB₃O₅ and their melts is proposed. Results suggest that the boron oxide species of LiB₃O₅ and CsB₃O₅ melts are in the form of six-membered rings B₃Ø₇ and B₃Ø₆ (Ø represents a bridging oxygen); Raman frequency of the symmetric breathing vibration of six-membered rings shifts to low frequency with the addition of BØ₄ tetrahedrons in rings; the relatively large amount of BØ₄ tetrahedrons is found in LiB₃O₅ melts. However, Cs⁺ ions with larger ion radius hinder the formation of BØ₄ tetrahedrons, and then reduc, the BØ₄/BØ₃ ratio of the melt. Finally, considering the growth mechanism of LiB₃O₅ and CsB₃O₅ crystals (Wang D, Wan S M et al. 2011 Cryst. Eng. Comm. 13 5239), we propose that the amount of BØ₄ tetrahedrons in melts, which is influenced by aikali metal ions, determines LiB₃O₅ and CsB₃O₅ crystallization habits, therefore, and suggest the reduction of BØ₄ tetrahedrons in melts is an effective way to crystallize LiB₃O₅.
Keywords： borate crystals melt structures Raman spectroscopy crystallization habit