Preparation and Crystallinity of Molybdenum and Tungsten Sulfides

Abstract

Abstract The sulfides of molybdenum and tungsten in the composition range MS 3 to MS 2 have been investigated. Molybdenum trisulfide was prepared by a variety of methods; the products were amorphous in all cases. The thermal decomposition of the trisulfide, leading to crystalline molybdenum disulfide, was studied by X‐ray diffraction and a model for the crystallization process is proposed. Molybdenum disulfide prepared by this method or from the elements always was of the hexagonal form. The rhombohedral form of molybdenum disulfide can be prepared from a molten medium; again, a model for the crystallization process is proposed. Quite analogous results were obtained for the tungsten sulfides: Tungsten trisulfide was always found to be amorphous. Tungsten disulfide prepared by thermal decomposition of the trisulfide or from the elements is of the hexagonal form, but a rhombohedral modification of tungsten disulfide could be prepared in the same way as the isotypic molybdenum compound. The unit‐cell dimensions of the disulfides are communicated.