LiBa₄Ga₅Q₁₂ (Q = S, Se): Noncentrosymmetric Metal Chalcogenides with a Cesium Chloride Topological Structure Displaying a Remarkable Laser Damage Threshold

The exploration of novel infrared nonlinear optical (IR NLO) materials with large second-harmonic generation (SHG) responses and wide band gaps has become very imperative recently. Herein we reported two noncentrosymmetric compounds, LiBa₄Ga₅Q₁₂ (Q = S, Se), crystallizing in space group P42₁c (No. 114), which feature 3D frameworks built by a basic [Ga₅Q₁₆]^17- windmill cluster and LiQ₄ tetrahedra in a cesium chloride topological structure. Both compounds satisfy the desired balance between good SHG responses (∼1.5× that of AgGaS₂) and wide band gaps (3.43 and 2.44 eV) with remarkable laser damage thresholds (21× and 6× that of AgGaS₂). The theoretical calculations uncover that the [Ga₅Q₁₆]^17- cluster makes major contributions to the SHG effect in LiBa₄Ga₅Q₁₂. In addition, the structure-performance relationship among all compounds in the I-II₄-III₅-VI₁₂ system has been discussed systematically, which indicates that the introduction of the alkali metal lithium in the I site is beneficial for the production of large band gaps. This work will be helpful in exploring novel IR NLO materials with special structures and comprehensive properties in the chalcogenide system.