A series of K3-xNaxB6O10Br (0.5 ≤ x ≤ 1.2) polycrystalline samples have been synthesized by the standard solid-state reaction method. Four stoichiometric crystals K3-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 K3-xNaxB6O10Br (x ≤ 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.
Key Laboratory of Functional Materials and Devices for Special Environments of CAS, Xinjiang Technical Institute of Physics and Chemistry of CAS, Chinese Academy of Sciences, 40-1 South Beijing Road, Urumqi 830011, China
Han, Shujuan,Wang, Ying,Pan, Shilie,et al. Noncentrosymmetric versus Centrosymmetric: Influence of the Na+ Substitution on Structural Transition and Second-Harmonic Generation Property[J]. Crystal Growth and Design,2014,14(4):1794-1801.