Noncentrosymmetric versus Centrosymmetric: Influence of the Na+ Substitution on Structural Transition and Second-Harmonic Generation Property

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• 作者：Shujuan Han ; Ying Wang ; Shilie Pan ; Xiaoyu Dong ; Hongping Wu ; Jian Han ; Yun Yang ; Hongwei Yu ; Chunyan Bai
• 刊名：Crystal Growth & Design
• 出版年：2014
• 出版时间：April 2, 2014
• 年：2014
• 卷：14
• 期：4
• 页码：1794-1801
• 全文大小：448K
• 年卷期：v.14,no.4(April 2, 2014)
• ISSN：1528-7505

文摘

A series of K_3鈥?i>xNa_xB₆O₁₀Br (0.5 鈮?x 鈮?1.2) polycrystalline samples have been synthesized by the standard solid-state reaction method. Four stoichiometric crystals K_3鈥?i>xNa_xB₆O₁₀Br (x = 0.13, 0.67, 1.30, 2.20) have been successfully grown from the high-temperature solution, and the crystal structures were determined by single-crystal X-ray diffraction. Interestingly, the Na⁺ concentration plays a profound role to influence the crystal structure. Up to about 23% (x = 0.7) K⁺ ions can be substituted by Na⁺ ions with the same noncentrosymmetric (NCS) crystal structure of K₃B₆O₁₀Br (space group R3m) being retained, while a higher Na concentration would lead to it crystallizing in the centrosymmetric (CS) space group Pnma. Meanwhile, the second-harmonic generation (SHG) response of K_3鈥?i>xNa_xB₆O₁₀Br (x 鈮?0.7) is about 2.8 times that of KDP, while the SHG response decreases sharply when x > 0.7 (the SHG response is zero at x = 1.3). After careful structural analysis, we believe that the different Br-M (M = K/Na, K, or Na) lattices, which are influenced by the coordination environments of the cations, are responsible for the structural changes from NCS to CS.