Birefringent　crystals　play　an　irreplaceable　role　in　optical　systems　by　adjusting　the　polarization　state　of　light　in　optical　devices.　This　work　successfully　synthesized　a　new　thiophosphate　phase　of　B-Pb3　P2　S8　through　the　high-temperature　solid-state　spontaneous　crystallization　method.　Different　from　the　cubic　a-Pb3　P2　S8　,　the　B-Pb3　P2　S8　crystallizes　in　the　orthorhombic　Pbcn　space　group.　Notably,　B-Pb3　P2　S8　shows　a　large　band　gap　of　2.37　eV　in　lead-based　chalcogenides,　wide　infrared　transparent　window　(2.5-15　mu　m),　and　excellent　thermal　stability.　Importantly,　the　experimental　birefringence　shows　the　largest　value　of　0.26@550　nm　in　chalcogenides,　even　larger　than　the　commercialized　oxide　materials.　The　Barder　charge　analysis　result　indicates　that　the　exceptional　birefringence　effect　is　mainly　from　the　Pb2　+　and　S2-　in　the　[PbSn　]　polyhedrons.　Meanwhile,　the　parallelly　arranged　polyhedral　layers　could　improve　the　structural　anisotropic.　Therefore,　this　work　supports　a　new　method　for　designing　chalcogenides　with　exceptional　birefringence　effect　in　the　infrared　region.　(c)　2024　Published　by　Elsevier　B.V.　on　behalf　of　Chinese　Chemical　Society　and　Institute　of　Materia　Medica,　Chinese　Academy　of　Medical　Sciences.