Hetero-Anionic Oxychalcogenides with Structures and Properties Tuned by the O:S Ratio

Abstract

Hetero-anionic compounds containing two or more anions, their structures, and their properties are expected to be tunable through varying anionic ratios, yet their rational structural design is still a great challenge. Herein, it is reported that the first family of hetero-anionic oxychalcogenides with their structures and properties are well-tuned by the varied O:S ratios. These compounds consist of the trigonal Sr₂(SnS₄)_2/3(SnOS₃)_1/3 (P3m1; O:S = 1:11), rhombohedral Sr₂(GeS₄)_4/9(GeOS₃)_5/9 (R3; O:S = 1:6.2), orthorhombic Sr₂[Ge(O_0.89/S_0.11)S₃] (Ama2; O:S = 1:3.5), and orthorhombic Ba₂(GeOS₃)_1/2(GeO₂S₂)_1/2 (Pnma; O:S = 1:1.7), which are all considered as the derivatives of Sr₂GeS₄ with different O and S substitutions. The interesting structural transformation among them can be attributed to the “symmetry-breaking” and “structure-directing” properties of hetero-anions. In addition, owing to the different electronegativity and polarizability of O and S atoms, the functional properties of these materials can be tuned based on the varied O:S ratios. Through rationally increasing the O:S ratio, an excellent infrared nonlinear optical crystal, Sr₂[Ge(O_0.89/S_0.11)S₃] exhibiting the best balance between large second harmonic generation response and wide band gap among all reported oxychalcogenides has been successfully designed. These will provide new insights for the rational design of hetero-anionic functional materials, especially for the non-centrosymmetric ones.