LiBa₂M^IIIQ₄ (M^III = Al, Ga, In; Q = S, Se): A Series of Metal Chalcogenides with a Structural Transition

Abstract

A series of metal chalcogenides, LiBa₂M^IIIQ₄ (M^III = Al, Ga, In; Q = S, Se), have been successfully obtained by the sealed-tube method. LiBa₂M^IIIQ₄ undergoes a special structural transformation from the <i>P</i>2₁/<i>m</i> (LiBa₂AlQ₄ and LiBa₂GaS₄) to the <i>P</i>2₁/<i>n</i> (LiBa₂InQ₄) space group, which leads to disparities in electronic states, birefringence, and band gaps. Their structures feature the same zigzag [LiM^IIIQ₄]^4- layers consisting of corner-shared LiQ₄ and M^IIIQ₄ tetrahedra. The Ba atoms serve to bridge the [LiM^IIIQ₄]^4- layers. The structural comparisons show that the radii of M^III and the coordination environments of the Ba atoms (BaQ₇ vs BaQ₈) cooperatively affect the structural transition from simple mirror <i>m</i> to diagonal glide <i>n</i> in LiBa₂M^IIIQ₄. In addition, a statistical analysis uncovers that the M^III/Ba atomic ratio also plays an important role in regulating the structural transition in Ba- and M^III-based chalcogenides.