NaCaGa3S6: a mixed alkali metal and alkaline earth metal sulfide with a distinctive [Ga5S10]∞ layered framework

Abstract

A new mixed alkali metal and alkaline earth metal sulfide, NaCaGa₃S₆, has been successfully synthesized and crystallizes in the orthorhombic Pbca space group. The compound features two distinct wavy layers, [Na₂Ca₂S₁₁]_∞ and [Ga₅S₁₀]_∞, which are alternately stacked and interconnected to form a three-dimensional network. Notably, the [Ga₅S₁₀]_∞ wavy layers are composed of GaS₄ tetrahedra that are linked through both corner-sharing and edge-sharing, a rare and unique structural characteristic. Property analysis shows that NaCaGa₃S₆ exhibits a wide band gap (3.68 eV), a broad transmission range (0.32–20 μm), and moderate birefringence (0.02 at 532 nm). These findings underscore the effectiveness of incorporating both alkali and alkaline earth metals into chalcogenide systems as a strategy to enrich structural chemistry and tailor material properties, positioning this system as a promising candidate for further exploration.