AGe2O4Q (A = Ba, Sr; Q = S, Se): A series of heteroanionic oxychalcogenides with large birefringence

Heteroanionic materials are of current research interest owing to their varied structural chemistry and properties. Recently, a number of heteroanionic materials have been synthesized that can be used for water splitting, battery materials, thermoelectrics , and nonlinear optical applications. Birefringent heteroanionic materials are still rarely researched. Herein, we report a series of new oxychalcogenides, AGe 2 O 4 Q (A = Ba, Sr; Q = S, Se), that are synthesized by solid-state reactions in fused silica tubes with their structures determined by single-crystal X-ray diffraction. Optical property measurements show that AGe 2 O 4 Q (A = Ba, Sr; Q = S, Se) exhibit large birefringences , 0.13–0.19 @ 1064 nm. These are one-order of magnitude larger than their single-anionic homologue, BaGe 2 O 5 - 0.03 @ 1064 nm. This suggests that constructing heteroanions through using chalcogenides to partially substitute O in tetrahedral foundation building units (FBUs) is a viable method for designing new birefringent materials. Furthermore, the crystal structures, UV–vis–NIR diffuse reflectance spectra, infrared and Raman spectra as well as the first-principles calculations for AGe 2 O 4 Q (A = Ba, Sr; Q = S, Se) are also reported.