ScSI: A New Exfoliatable Semiconductor

ScSI, a missing member of the rare earth sulfoiodide (RESI) family of materials, has been synthesized for the first time. ScSI crystallizes in the FeOCl structure type, space group Pmmn (No. 59), a = 3.8904(2), b = 5.0732(9), c = 8.9574(6) Å. Both hyperspectral reflectance measurements and ab initio calculations support the presence of an indirect optical band gap of 2.0 eV. The bulk crystal is found to be readily exfoliatable, enabling its use as an optical component in novel heterostructures. The impact of lithium intercalation on its electronic band structure is also explored. A broader correlation is drawn between the observed structural trends in all known 1:1:1 sulfoiodide phases, cationic proportions, and electronic considerations. The realization of this phase both fills a significant synthetic gap in the literature and presents a novel exfoliatable phase for use as an optical component in next-generation heterostructure devices.