The preparation, properties, and crystal structures of some scandium sulfides in the range Sc2S3-ScS

Article abstract of DOI:10.1021/ic50019a004

Scandium sesquisulfide, Sc₂S₃, was prepared by the high-temperature reaction of hydrogen sulfide with scandium sesquioxide. Due to the problem of stoichiometry associated with the high melting point, 1775°, stoichiometric crystals of Sc₂S₃ were prepared by chemical transport with I₂ at 950°. A nonstoichiometric material containing an excess of scandium compared with Sc₂S₃ was prepared by heating Sc₂S₃ under vacuum at 1650°. Crystals of ScS were prepared by the reaction of scandium metal with sulfur. The crystal structure of Sc₂S₃ is closely related to that of NaCl, but the unit cell is twelve times as large due to a complex ordering arrangement of the cation voids. Each octahedron surrounding sulfur has two vertices empty, and the bond angles are all very close to 90°. The nonstoichiometric material has a much simpler structure which is also closely related to that of NaCl, with Sc_1.37S₂ per rhombohedral unit cell. This structure, in which one cation site is filled and the other is only partially occupied, could exist over the whole range between Sc₂S₃ and ScS, which was found to have the NaCl structure. Stoichiometric Sc₂S₃ is a semiconductor with a band gap of about 2 e.V., but the materials between Sc₂S₃ and ScS are good electrical conductors. Electrical conduction in the latter materials appears to involve a 3d band.