cg4019103_si_007.cif (16.2 kB)
Noncentrosymmetric versus Centrosymmetric: Influence of the Na+ Substitution on Structural Transition and Second-Harmonic Generation Property
dataset
posted on 2014-04-02, 00:00 authored by Shujuan Han, Ying Wang, Shilie Pan, Xiaoyu Dong, Hongping Wu, Jian Han, Yun Yang, Hongwei Yu, Chunyan BaiA 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–xNaxB6O10Br (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.