Molybdenum and Niobium Sulphides

Abstract

IN the system Mo-S the only compound that is formed by direct synthesis from the elements is the disulphide MoS₂. This compound exists in two modifications : (1) The well-known hexagonal form (a=3.16 ; c=12.29 A.), the structure of which¹ is shown in Fig. 1a. (2) The rhombohedral form (a=3.17 ; c=18.38 A.) which was first described by Bell and Herfert². These authors propose a CdCl₂-type structure which, however, is incompatible with their own and our X-ray diffraction data. Good agreement is found for the structure shown in Fig. 1b. This structure can be described in space-group R3m—C ⁵ _3ν : 3 Mo situated in 3(a) ; 0 0 z, etc., with z=0 ; 3 S I in 3(a) with z≈¼ and 3 S II in 3(a) with z≈5/12.