BaHgGaS: A Zero-Dimensional Quaternary Sulfide Featuring a Unique [HgGaS] 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, BaHgGaS (BHGS), is obtained by a solid-state reaction at 1123 K. It crystallizes in the monoclinic space group 2/, and its zero-dimensional structure features two seesaw-like HgS units and four GaS tetrahedra, constructing a unique [HgGaS] 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 AEMMQ (AE = Mg, Ca, Sr, Ba; M = Zn, Cd, Hg; M = Al, Ga, In; Q = S, Se) chalcogenides.