Ba 3 HgGa 2 S 7 : A Zero-Dimensional Quaternary Sulfide Featuring a Unique [Hg 2 Ga 4 S 14 ] 12- String and Exhibiting a High Photocurrent Response.

The discovery of new types of metal sulfides is attractive because of their rich structures and diverse physical properties. Here, a novel quaternary sulfide, Ba 3 HgGa 2 S 7 (BHGS), is obtained by a solid-state reaction at 1123 K. It crystallizes in the monoclinic space group P 2 1 / c , and its zero-dimensional structure features two seesaw-like HgS 2 units and four GaS 4 tetrahedra, constructing a unique [Hg 2 Ga 4 S 14 ] 12- string. BHGS has a wide band gap of 3.64 eV and a large birefringence of 0.09 at 2100 nm. Specifically, BHGS exhibits a remarkable photocurrent response. This work may be extended to a new family of AE 3 M II M III 2 Q 7 (AE = Mg, Ca, Sr, Ba; M II = Zn, Cd, Hg; M III = Al, Ga, In; Q = S, Se) chalcogenides.