Structure and phase transitions of molybdenum(III) sulfide and some related phases

Molybdenum(III) sulfide, Mo2.06S3, is monoclinic with a = 6.092Å; b = 3.208Å; c = 8.6335Å; β = 102.43°. The structure has been determined and refined from X-ray powder data. The metal atoms lie in octahedral holes of a chh close packing of sulfur, but they are displaced from the octahedron centers in such a way that zigzag MoMo chains are formed (MoMo = 2.86 Å). Blow + 37°C the structure is a superstructure of the one described, all axes being doubled. At −80°C the lattice of Mo2.06S3 undergoes a distortion to triclinic symmetry. In solid solutions (Mo1−x,Nbx)2.06S3 with 0.025 < x ⩽ 0.50 no superstructures are observed; the structure remains monoclinic down to low temperatures. The compounds previously regarded as Mo2Se3 and Mo2Te3 are better designated as Mo3Se4 and Mo3Te4. The low-temperature Guinier camera used in this investigation is described.