ReSe₂: A reassessment of crystal structure and thermal analysis

The rhenium-based layered dichalcogenide ReSe₂ crystallizes in a distorted triclinic structure which results in unique, anisotropic electronic and optical properties. This, along with a weak layer-dependence of band gap has made ReSe₂ a subject of intense contemporary research interest. However, there has been no agreement on the exact crystal structure of this material, or knowledge of its thermal properties like the melting point. In this work, we perform single crystal, Laue, and powder diffraction measurements on high-quality ReSe₂ crystals synthesized using a modified Bridgman technique. We confirm the presence of triclinic symmetry (-space group) and support the view that that ReSe₂ has a distorted CdCl₂-type structure (rather than Cd(OH)₂ as initially proposed) and obtain lattice parameter values of a = 6.5791(8) Å, b = 6.6897(10) Å, and c = 6.7013(11) Å. Further, thermal measurements on these crystals show a clear endothermic peak at around 1115 °C pointing to a melting transition, and show no other phase transitions up to 1300 °C.