Chiral and Polar Duality Design of Heteroanionic Compounds: Sr<sub>18</sub>Ge<sub>9</sub>O<sub>5</sub>S<sub>31</sub> Based on [Sr<sub>3</sub>OGeS<sub>3</sub>]<sup>2+</sup> and [Sr<sub>3</sub>SGeS<sub>3</sub>]<sup>2+</sup> Groups
Shaoxin Cui, Hongping Wu, Xinkang Dong, Zhanggui Hu, Jiyang Wang, Yicheng Wu, Kenneth R. Poeppelmeier, Hongwei Yu
Abstract
Abstract Chirality and polarity are the two most important and representative symmetry‐dependent properties. For polar structures, all the twofold axes perpendicular to the principal axis of symmetry should be removed. For chiral structures, all the mirror‐related symmetries and inversion axes should be removed. Especially for duality (polarity and chirality), all of the above symmetries should be broken and that also represents the highest‐level challenge. Herein, a new symmetry‐breaking strategy that employs heteroanionic groups to construct hourglass‐like [Sr 3 OGeS 3 ] 2+ and [Sr 3 SGeS 3 ] 2+ groups to design and synthesize a new oxychalcogenide Sr 18 Ge 9 O 5 S 31 with chiral‐polar duality is proposed. The presence of two enantiomers of Sr 18 Ge 9 O 5 S 31 is confirmed by the single‐crystal X‐ray diffraction. Its optical activity and ferroelectricity are also studied by solid‐state circular dichroism spectroscopy and piezoresponse force microscopy, respectively. Further property measurements show that Sr 18 Ge 9 O 5 S 31 possesses excellent nonlinear optical properties, including the strong second harmonic generation efficiency (≈2.5 × AGS), large bandgap (3.61 eV), and wide mid‐infrared transparent region (≈15.3 µm). These indicate that the unique microstructure groups of heteroanionic materials are conducive to realizing symmetry‐breaking and are able to provide some inspiration for exploring the chiral‐polar duality materials.