LiBa2MIIIQ4 (MIII = Al, Ga, In; Q = S, Se): A Series of Metal Chalcogenides with a Structural Transition.

A series of metal chalcogenides, LiBa2MIIIQ4 (MIII = Al, Ga, In; Q = S, Se), have been successfully obtained by the sealed-tube method. LiBa2MIIIQ4 undergoes a special structural transformation from the P21/m (LiBa2AlQ4 and LiBa2GaS4) to the P21/n (LiBa2InQ4) space group, which leads to disparities in electronic states, birefringence, and band gaps. Their structures feature the same zigzag [LiMIIIQ4]4- layers consisting of corner-shared LiQ4 and MIIIQ4 tetrahedra. The Ba atoms serve to bridge the [LiMIIIQ4]4- layers. The structural comparisons show that the radii of MIII and the coordination environments of the Ba atoms (BaQ7 vs BaQ8) cooperatively affect the structural transition from simple mirror m to diagonal glide n in LiBa2MIIIQ4. In addition, a statistical analysis uncovers that the MIII/Ba atomic ratio also plays an important role in regulating the structural transition in Ba- and MIII-based chalcogenides.